HciDjig; F. A. BEOCKHAUS. aeta gDtlt; THE MACMILLAN COMPANY,nbsp;l�ombag anti Calcutta: MACMILLAN AND CO., liXD*

AT THE UNIVERSITY PRESS. .nbsp;nbsp;nbsp;nbsp;1898

1577 0807

Cambri�ge:

PEEFACE.

TN acceding to Mr Shipley�s request to write a book on Fossil Plants for the Cambridge Natural History Series,

1 am well aware that I have undertaken a work which was considered too serious a task by one who has been called anbsp;�founder of modern Palaeobotany.� I owe more than I amnbsp;able to express to the friendship and guidance of the latenbsp;Professor Williamson; and that I have attempted a work tonbsp;'which he consistently refused to commit himself, requires anbsp;Word of explanation. My excuse must be that I have endeavoured to write a book which may render more accessiblenbsp;to students some of the important facts of Palaeobotany, andnbsp;suggest lines of investigation in a subject which Williamsonnbsp;had so thoroughly at heart.

The subject of Palaeobotany does not readily lend itself to adequate treatment in a work intended for both geologicalnbsp;and botanical students. The Botanist and Geologist are notnbsp;always acquainted with each other�s subject in a sufficientnbsp;degree to appreciate the significance of Palaeobotany in itsnbsp;several points of contact with Geology and recenk Botany. Inbsp;have endeavoured to bear in mind the possibility that thenbsp;following pages maj' be read by both non-geological and non-botanical students. It needs but a slight acquaintance withnbsp;Geology for a Botanist to estimate the value of the mostnbsp;important applications of Palaeobotany; on the other hand,nbsp;the bearing of fossil plants on the problems of phylogeny and

descent cannot be adequately understood without a fairly intimate knowledge of recent Botany.

The student of elementary geology is not as a rule required to concern himself with vegetable palaeontology, beyond anbsp;general acquaintance with such facts as are to be found innbsp;geological text-books. The advanced student will necessarilynbsp;find in these pages much with which he is already familiar; butnbsp;this is to some extent unavoidable in a book which is writtennbsp;with the dual object of appealing to Botanists and Geologists.nbsp;While considering those who may wish to extend their botanicalnbsp;or geological knowledge by an acquaintance with Palaeobotany,nbsp;my aim has been to keep in view the requirements of thenbsp;student who may be induced to approach the subject fromnbsp;the standpoint of an original investigator. As a possiblenbsp;assistance to those undertaking research in this promisingnbsp;field of work, I have given more references than may seemnbsp;appropriate to an introductory treatise, and there are certainnbsp;questions dealt with in greater detail than an elementarynbsp;treatment of the subject requires. In several instances references are given in the text or in footnotes to specimens ofnbsp;Coal-Measure plants in the Williamson cabinet of microscopicnbsp;sections. Now that this invaluable collection of slides hasnbsp;been acquired by the Trustees of the British Museum, thenbsp;student of Palaeobotany has the opportunity of investigatingnbsp;for himself the histology of Palaeozoic plants.

My plan has been to deal in some detail with certain selected types, and to refer briefly to such others as shouldnbsp;be studied by anyone desirous of pursuing the subject morenbsp;thoroughly, rather than to cover a wide range or to attemptnbsp;to make the list of types complete. Of late years there has beennbsp;a much wider interest evinced by Botanists in the study ofnbsp;fossil plants, and this is in great measure due to the valuablenbsp;and able work of Graf zu Solms-Laubach. His Einleitung in dienbsp;Palaeophytologie must long remain a constant book of referencenbsp;for those engaged in palaeobotanical work. While referring to

Mr Wethered of Cheltenham and others have assisted me in a similar manner. I would also express my gratitude to Dr Hoylenbsp;of Manchester, Mr Platnauer of York, and Mr Rowntreenbsp;of Scarborough for the loan of specimens.

To Dr Henry Woodward of the British Museum I am indebted for the loan of the woodblocks made use of innbsp;figs. 10, 47, 60, 66, and 101, and to Messrs Macmillan for thenbsp;process-block of fig. 25.

For the photographs reproduced in figs. 15, 34, 68, 102 and 103 I owe an acknowledgment to Mr Edwin Wilson ofnbsp;Cambridge, and to my friend Mr C. A. Barber for the microphotograph made use of in fig. 40.

In conclusion I wish more particularly to thank my wife, who has drawn by far the greater number of the illustrations,nbsp;and has in many other ways assisted me in the preparationnbsp;of this Volume.

In Volume II the Systematic treatment of Plants will be concluded, and the last chapters will be devoted to suchnbsp;subjects as geological floras, plants as rock-builders, fossilnbsp;plants and evolution, and other general questions connectednbsp;with Palaeobotany.

TABLE OE CONTENTS.

PAET I. GENERAL.

CHAPTER I.

HISTORICAL SKETCH. Pp. 1�11.

Fossil plants and the Flood. Sternberg and Brongniart. The internal structure of fossil plants. English Palaeobotani.sts. , Difficulties ofnbsp;identification.

CHAPTER II.

RELATION OF PALAEOBOTANY TO BOTANY AND GEOLOGY. Pp. 12�21.

Fleglect of fossils by Botanists. Fossil plants and distribution. Fossil plants and climate. Fossil plants and phylogeny.

CHAPTER III.

GEOLOGICAL HISTORY. Pp. 22�53.

Rock-building. Calcareous rocks. Geological sections. Inversion of strata. Table of Strata :

1. Archaean, 34-36. II. Cambrian, 36-37. III. Ordovician, 37-38. IV. Silurian, 38. V. Devonian, 39. VI. Carboniferous,nbsp;39-45. VII. Permian, 45-47. VIII. Trias, 47-48. IX. Jurassic, 48-49. X. Cretaceous, 50-51. XI. Tertiary, 51-53. Geologicalnbsp;Evolution.

CHAPTER V.

DIFFICULTIES AND SOURCES OF ERROR IN THE DETERMINATION OF FOSSIL PLANTS. Pp. 93�109.

External resemblance. Venation characters. Decorticated stems. Imperfect casts. Mineral deposits simulating plants. Traces ofnbsp;wood-borers in petrified tissue. Photography and illustration.

CHAPTER VI.

NOMENCLATURE. Pp. 110�115.

PAE� II. SYSTEMATIC.

CHAPTER VII.

1. nbsp;nbsp;nbsp;SCHIZOPHYCEAE (Cyanophyceae) .nbsp;nbsp;nbsp;nbsp;.nbsp;nbsp;nbsp;nbsp;. 122-132

Bacillus Permicus 135-136. B. Tieghemi and Micrococcus Owignardi 136. Fossil Bacteria 137-138.

Scarcity of fossil algae. Fossils simulating Algae. Recognition of fossil algae. Algites tiic.

Godiwni 159-160. Sphaerocodium 160. Peni-cillus 161. Ovidites 161-164. Halinieda 164.

Cymopolia 169-171. Venniporella 172-173. Sycidiuni 173. Diplopora 174-175. Gyroporella 175. Dactylopora, Palaeozoicnbsp;and Mesozoic Siphoneae 175-177.

Pathology of fossil tissues. Oochytrium Lepido-dendri 216-217. Peronosporites antiquarms 217-220. Gladosporites hipartitus 220. Hap-tographites cateniger 220. Zygosporites 220-221.

jl/M�CTtes 238-241. M. polytrkhaceiis�iSQ-^40. Palaeozoic Mosses. Muscites ferrugineus 241.

Equisetites Hemingwayi 263-264. E. �patulatus 264-266. E. zeaeformis 266. E. arenacem 268-269.nbsp;E. columnaris 269-270. E. Beani 270�275. E.nbsp;lateralis 275-279. E. Burchardti 279-280.nbsp;Phyllotheca 281-291.

Phyllotheca deliquescens 283-284. P. Brongniarti 286-287. P. indica and P. aiistralis 287-289.nbsp;Schizoneura 291-294.

CHAPTER X.

EQUISETALES (continued). Pp. 295�388.

I- Historical sketch....... 295-302

II. nbsp;nbsp;nbsp;Description of the anatomy of Calamites .nbsp;nbsp;nbsp;nbsp;. 302-364

Arthropitys, Arthrodendron, and Galamodendron. h. Leaves .........nbsp;nbsp;nbsp;nbsp;329-342

355-357. Palaeostachya vera 358-360. Calamostachys, Palaeostachya and Alacrostachya 361-364.

III. nbsp;nbsp;nbsp;Pith-casts of Calamites...... 365-380

Qiipperti 372-374. Stylocalamites 374-376. G. (Stylocalamites) Smhowi 374-376. Eiiccdamitesnbsp;376-379. C. (Eucalamites) cruciatns 378-379.

CHAPTER XI.

SPHENOPHYLLALES. Pp. 389�414.

I. nbsp;nbsp;nbsp;The anatomy of Sphenophyllum .... 392-406

b. nbsp;nbsp;nbsp;Rootsnbsp;nbsp;nbsp;nbsp;.nbsp;nbsp;nbsp;nbsp;.nbsp;nbsp;nbsp;nbsp;.......399

II. nbsp;nbsp;nbsp;Types of vegetative Branches of Sphenophyllum 407-412nbsp;Sphenophyllum emarginatum 407-408. S. trichoma-

III. nbsp;nbsp;nbsp;Affinities,nbsp;nbsp;nbsp;nbsp;Range and Habit of Sphenophyllum . 412-414

LIST OF ILLUSTRATIONS.

�bonti.spiece. Tree Stdmps in a Carboniferous Forest. from a photograph. (M. Seward.) Page .57.

27. nbsp;nbsp;nbsp;Fish-scale and shell pei-forated by a boring orgiinism- (M. S.)

28. nbsp;nbsp;nbsp;Bacillus Tieghemi Ken. and Micrococcus Guignardi Ren. (M. S.)

30. nbsp;nbsp;nbsp;Rill-mark ; trail of a seaweed ; tracks of a Polychaet. (M. S.)

Bactryllinm deplanatnm Heer; Calcareous pebble from a lake in Michigan. (M. S.)nbsp;nbsp;nbsp;nbsp;...

Adcndaria sj).; A. Bchencki (Mob.); A. Mediterranea Lamx.; Ovulites margaritula Lam.x.; Pmw�lus pyra-midalis (Lamx.) (M. S.) .

and Memecylon with vacuolated contents ; Peronosporites antiquarius Smith ; Zygosporites .....

42. nbsp;nbsp;nbsp;Tracheids of coniferous wood attacked by Trametes radiciperda

46. nbsp;nbsp;nbsp;. Chara Bleicheri SiSu\gt;. I Chara? sp.; C. IFrig'Att Forbes. (M. S.)

48. nbsp;nbsp;nbsp;Tristichia hypnoides Spreng. ; Podocarpus cupn-essina Br. and

Equisetites g�paiulatug Zeill.; E. zeo^formts (Schloth.) ; Equi-setites lateralis Phill. ; Equisetites colwyinaris Brongu. Equisetum trachyodon A. Br. (M. S.)

'� nbsp;nbsp;nbsp;E.nbsp;nbsp;nbsp;nbsp;Yokoyamae Sew. (Fromnbsp;nbsp;nbsp;nbsp;a block lent by Dr Woodward) 2

1- Transverse section of a yonng Calamite stem 2. Longitudinal and transverse sections of Calamites

Longitudinal section (tangential) of Calamites (Artkropitys) sp. Longitudinal section (tangential) of Calamites {Arthropitys) sp.

� nbsp;nbsp;nbsp;1 Transverse and longitudinal (radial) section.s of a thick Calamite

^1. Longitudinal .section of a joxmg Calamite nbsp;nbsp;nbsp;.nbsp;nbsp;nbsp;nbsp;.nbsp;nbsp;nbsp;nbsp;.nbsp;nbsp;nbsp;nbsp;�

A'linulana stellata (Schloth.) (M. S.) nbsp;nbsp;nbsp;.nbsp;nbsp;nbsp;nbsp;�nbsp;nbsp;nbsp;nbsp;�nbsp;nbsp;nbsp;nbsp;�nbsp;nbsp;nbsp;nbsp;�

bo. Pith-cast of a Calamite, with roots. (M. S.) bl. Transverse sections of Calamite rootsnbsp;92. Boot given off from a Calamite stemnbsp;06. Oalamostarhys sp. (M. S.)nbsp;nbsp;nbsp;nbsp;.nbsp;nbsp;nbsp;nbsp;.nbsp;nbsp;nbsp;nbsp;.nbsp;nbsp;nbsp;nbsp;.

XVlll

PIG.

94.

95.

96.

97.

98.

99. 100.

101.

102.

103.

104.

105.

106.

107.

108.

109.

110. 111.

PAGE

352

354

356

357 359nbsp;368

370

373

377

385

393

394

398

400

402

407

410

411

Catamites {Eucatamites) cruciatus Sternb. (From a photograph by Mr Edwin Wilson)......

Archaeocatamites scrobiculatus (Schloth.). (From a photograph by Mr Edwin Wilson)......

Transverse and longitudinal sections of Sphenophyttum insigne (Will.) and S. pturifotiatum Will, and Scott .

Sphenophyttum pturifotiatum Will, and Scott. (From a photograph by Mr Highley) ......

Diagrammatic longitudinal section of a Sphe'twphytlum strobilus. (M. S.)nbsp;nbsp;nbsp;nbsp;.

Note. The references in the footnotes require a word of explanation. The titles of the works referred to will be found innbsp;the Bibliography at the end of the volume. In this list the authors�nbsp;names are arranged alphabetically and the papers of each author arenbsp;in chronological order. The numbers in brackets after the author�snbsp;name in the footnotes, and before his name in the bibliographicalnbsp;list, refer to the year of publication. Except in cases where thenbsp;works were published prior to 1800, the first two figures arenbsp;omitted: thus Ward (84) refers to a paper published by L. F. Wardnbsp;in 1884. This system was suggested by Dr H. H. Field in thenbsp;Biologisches Centralhlatt, vol. xiii. 1893, p. 753. {Ueber die Art dernbsp;Abfassung naturwissenschafilicher Litterahirverzeichnisse.)

PAI^T I. GENEEAL.

CHAPTER I.

� But particular care ought to be had not to consult or take relations from any but those who appear to have been both long conversant in thesenbsp;affairs, and likewise persons of Sobriety, Faithfulness and Discretion, tonbsp;avoid the being misled and imposed upon either by falsehood, or thenbsp;ignorance, credulity, and fancifulness, that some of these people are butnbsp;too obnoxious unto.� John Woodward, 1728.

The scientific study of fossil plants dates from a comparatively recent period, and palaeobotany has only 'attained a real importance in the eyes of botanists and geologists duringnbsp;the last few decades of the present century. It would be outnbsp;of place, in a short treatise like the present, to attempt anbsp;detailed historical sketch, or to give an adequate account ofnbsp;the gradual rise and development of this modem science. Annbsp;excellent Sketch of Palaeobotany has recently been drawn upnbsp;by Prof. Lester Wardh of the United States Geological Survey,nbsp;and an earlier historical retrospect may be found in the introduction to an important work by an eminent German palaeobotanist,nbsp;the late Prof Goppert�. In the well-known work by Parkinsonnbsp;on The Organic Remains of a Former World^ there is muchnbsp;interesting information as to the early history of our knowledge

of fossil plants, as well as a good exposition of the views held at the beginning of this century.

As a means of bringing into relief the modern development of the science of fossil plants, we may briefly pass in reviewnbsp;some of the earlier writers, who have concerned themselves in anbsp;greater or less degree with a descriptive or speculative treatmentnbsp;of the records of a past vegetation. In the early part of thenbsp;present century, and still more in the eighteenth century, thenbsp;occurrence of fossil plants and animals in the earth�s crustnbsp;formed the subject of animated, not to say acrimonious,nbsp;discussion. The result was that many striking and ingeniousnbsp;theories were formulated as to the exact manner of formation of fossil remains, and the part played by the watersnbsp;of the deluge in depositing fossiliferous strata. The earliernbsp;views on fossil vegetables are naturally bound up with thenbsp;gradual evolution of geological science. It is from Italy thatnbsp;we seem to have the first glimmering of scientific views;nbsp;but we are led to forget this early development of morenbsp;than three hundred years ago, when we turn to the writingsnbsp;of English and other authors of the eighteenth century.nbsp;� Under these white banks by the roadside,� as a writer onnbsp;Verona has expressed it, �was born, like a poor Italian gipsy,nbsp;the modern science of geology.� Early in the sixteenth centur}'^nbsp;the genius of Leonardo da Vinci^ compelled him to adoptnbsp;a reasonable explanation of the occurrence of fossil shells innbsp;rocks far above the present sea-level. Another Italian writer,nbsp;Fracastaro, whose attention was directed to this matter by thenbsp;discovery of numerous shells brought to light by excavationsnbsp;at Verona, expressed his belief in the organic nature of thenbsp;remains, and went so far as to call in question the Mosaicnbsp;deluge as a satisfactory explanation of the deposition of fossilbearing strata.

The partial recognition by some observers of the true nature of fossils marks the starting point of more rationalnbsp;views. The admission that fossils were not mere sportsnbsp;of nature, or the result of some wonderful � vis lapidifica,�

1 For an account of the early views on fossils, v. Lyell (67), Vol. i. Vide also Leonardo da Vinci (83).

was naturally followed by numerous speculations as to the manner in which the remains of animals and plants came to benbsp;embedded in rocks above the sea-level. For a long time, thenbsp;� universal flood � was held responsible by nearly all writersnbsp;for the existence of fossils in ancient sediments. Dr Johnnbsp;Woodward, in his Essay toward a Natural History of thenbsp;Earth, propounded the somewhat revolutionary theory, thatnbsp;the whole terrestrial globe was taken all to pieces and dissolved at the Deluge, the particles of stone, marble, and allnbsp;solid fossils dissevered, taken up into the water, and therenbsp;sustained together with sea-shells and other animal and vegetable bodies; and that the present earth consists, and wasnbsp;formed out of that promiscuous mass of sand, earth, shells,nbsp;and the rest falling down again, and subsiding from thenbsp;Watert� In common with other writers, he endeavoured tonbsp;fix the exact date of the flood by means of fossil plants.nbsp;Speaking of some hazel-nuts, w'hich were found in a Cheshirenbsp;moss pit, he draws attention to their unripened condition, andnbsp;adds; � The deluge came forth at the end of May, when nutsnbsp;are not ripe.� As additional evidence, he cites the occurrence ofnbsp;� Pine cones in their vernal state,� and of some Coal-Measurenbsp;fossils which he compares with Virginian Maize, �tender,nbsp;young, vernal, and not ripenedl� Woodward (1665�1728)nbsp;was Professor of Physic in Gresham College; he bequeathednbsp;his geological collections to the University of Cambridge, andnbsp;founded the Chair w'hich bears his name.

Another writer, Mendes da Costa, in a paper in the Philosophical Transactions for 1758, speaks of the impressions of � ferns and reed-like plants � in the coal-beds, and describesnbsp;some fossils {Sigillaria and Stigmaria) as probably unknownnbsp;forms of plant life*.

Here we have the suggestion that in former ages there were plants which differed from those of the present age.nbsp;Discussing the nature of some cones {Lepidostrobi) from the ironstone of Coalbrookdale in Shropshire, he concludes : � I firmlynbsp;believe these bodies to be of vegetable origin, buried in the

strata of the Earth at the time of the universal deluge recorded by Moses.� Scheuchzer of Zurich, the author of one of thenbsp;earliest works on fossil plants and a �great apostle of thenbsp;Flood Theory,� figures and describes a specimen as an earnbsp;of com, and refers to its size and general appearance asnbsp;pointing to the month of May as the time of the delugehnbsp;Another English writer. Dr Parsons, in giving an account ofnbsp;the well-known 'fossil fruits and other bodies found in thenbsp;island of Sheppey,� is disposed to dissent from Woodward�snbsp;views as to the time of the flood. He suggests that the factnbsp;of the Sheppey fruits being found in a perfectly ripe condition,nbsp;points to the autumn as the more probable time for the occurrence of the deluge�.

In looking through the works of the older writers, and occasionally in the pages of latter-day contributors, we frequently find curiously shaped stones, mineral markings on rocknbsp;surfaces, or certain fossil animals, described as fossil plants. Innbsp;Plot�s Natural History of Oxfordshire, published in 1705, anbsp;peculiarly shaped stone, probably a flint, is spoken of as onenbsp;of the�Fungi lethales non esculent!��; and again a piece ofnbsp;coral* is compared with a � Bryony root broken off transversely.�nbsp;On the other hand, that we may not undervalue the painstaking and laborious efforts of those who helped to lay thenbsp;foundations of modern science, we may note that such authorsnbsp;as Scheuchzer and Woodward were not misled by the mosslike or dendritic markings of oxide of manganese on thenbsp;surface of rocks, which are not infrequently seen to-day in thenbsp;cabinets of amateurs as specimens of fossil plants.

The oldest figures of fossil plants from English rocks which are drawn with any degree of accuracy are those of Coal-Measure ferns and other plants in an important work bynbsp;Edward Lhwyd published at Oxford in 1760�.

Passing beyond these prescientific speculations, brief reference may be made to some of the more eminent pioneers of palaeobotany. The Englishman Artis� deserves mention for

1 Scheuchzer (1723), p. 7, PI. i. fig. 1. 3 Plot (1705), p. 125, PI. VI. fig. 2.

the quality rather than the quantity of his contributions to Palaeozoic botany ; and among American authors Steinhauer�s^nbsp;name must hold a prominent place in the list of those who helpednbsp;to found this branch of palaeontology. Among German writers,nbsp;Schlotheim stands out prominently as one who first publishednbsp;a work on fossil plants which still remains an important booknbsp;of reference. Writing in 1804-, he draws attention to thenbsp;neglect of fossils from a scientific standpoint, they are simplynbsp;looked upon, he says, as � unimpeachable documents of thenbsp;flood�.� His book contains excellent figures of many Coal-Measure plants, and we find in its pages occasional^ comparisons of fossil species with recent plants of tropical latitudes.nbsp;Among the earlier authors whose writings soon become familiarnbsp;to the student of fossil plants, reference must be made to Grafnbsp;Sternberg, who was horn three years before Schlotheim, butnbsp;whose work came out some years later than that of the latter.

His great contribution to Fossil Botany entitled Versuch einer S^ognostisch-botanischen Darstellung der Flora der Vorwelt, wasnbsp;published in several parts between the years 1820 and 1838;nbsp;it was drawn up with the help of the botanist Presl, andnbsp;included a valuable contribution by Gorda�. In addition tonbsp;descriptions and numerous figures of plants from several geological horizons, this important work includes discussions onnbsp;the formation of coal, with observations on the climates of past

Sternberg endeavoured to apply to fossil plants the same niethods of treatment as those made xise of in the case of recentnbsp;species. About the same time as Sternberg s earlier partsnbsp;were published, Adolphe Brongniart^ of Paris began to enrichnbsp;palaeohotanical science by those splendid researches whichnbsp;have won for him the title of the �Father of palaeohotany. Innbsp;Brongniart�s Prodrome, and Histoire des v�g�taux fossiles, andnbsp;later in his Tableau des genres de v�g�tawx fossiles, we have notnbsp;merely careful descriptions and a systematic arrangement ofnbsp;the known species of fossil plants, but a masterly scientific

treatise on palaeobotany in its various aspects, which has to a large extent formed the model for the best subsequent worksnbsp;on similar lines. From the same author, at a later date, therenbsp;is at least one contribution to fossil plant literature whichnbsp;must receive a passing notice even in this short sketch. Innbsp;1839 he published an exhaustive account of the minutenbsp;structure of one of the well-known Palaeozoic genera, Sigillaria;nbsp;this is not only one of the best of the earliest monographs onnbsp;the histology of fossil species, but it is one of the few existingnbsp;accounts of the internal structure of this common typeh Thenbsp;fragment of a Sigillarian stem which formed the subject ofnbsp;Brongniart�s memoir is in the Natural History Museum in thenbsp;Jardin des Plantes, Paris. It affords a striking example ofnbsp;the perfection of preservation as well as of the great beautynbsp;of the silicified specimens from Autun, in Central France.nbsp;Brongniart was not only a remarkably gifted investigator,nbsp;whose labours extend over a period connecting the older andnbsp;more crude methods of descriptive treatment with the modernnbsp;development of microscopic analysis,, but he possessed thenbsp;power of inspiring a younger generation with a determinationnbsp;to keep up the high standard of the palaeobotanical achievements of the French School. In some cases, indeed, his disciplesnbsp;have allowed a natural reverence for the Master to warpnbsp;their scientific judgement, where our more complete knowledgenbsp;has naturally led to the correction of some of Brongniart�s conclusions. Without attempting to follow the history of the sciencenbsp;to more recent times, the names of Heer, Lesquereux, Zigno,nbsp;Massalongo, Saporta and Ettingshausen should be includednbsp;among those who rendered signal service to the science of fossilnbsp;plants. The two Swiss writers. Heer* and Lesquereux�, contributed numerous books and papers on palaeobotanical subjects,nbsp;the former being especially well known in connection with thenbsp;fossil floras of Switzerland and of Arctic lands, and the latternbsp;for his valuable writings on the fossil plants of his adoptednbsp;country, North America. Zigno^ and Massalongo� performednbsp;like services for Italy, and the Marquis of Saporta�s name will

always hold an honourable and prominent position in the list of the pioneers of scientific palaeobotany; his work on thenbsp;Tertiary and Mesozoic floras of France being specially noteworthy among the able investigations which we owe to hisnbsp;ability and enthnsiasmb In Baron Ettingshausen'^ we havenbsp;another representative of those students of ancient vegetationnbsp;who have done so much towards establishing the science ofnbsp;fossil plants on a philosophical basis.

As in other fields of Natural Science, so also in a marked degree in fossil botany, a new stimulus was given to scientificnbsp;inquiry by the application of the microscope to palaeobotanicalnbsp;investigation. In 1828 Sprengel published a work entitlednbsp;Commentatio de Psarolithis, ligni fossilis genere �; in which henbsp;dealt in some detail with the well-known silicified fern-stemsnbsp;of Palaeozoic age, from Saxony, basing his descriptions on thenbsp;characteristics of anatomical structure revealed by microscopicnbsp;examination.

In 1833 Henry Witham of Lartington brought out a work on The Internal Structure of Fossil Vegetahles*; thisnbsp;book, following the much smaller and less important worknbsp;by Sprengel, at once established palaeobotany on a firmernbsp;scientific basis, and formed the starting point for thosenbsp;more accurate methods of research, which have yielded suchnbsp;astonishing results in the hands of modern workers. Innbsp;the introduction Witham writes, �My principal object innbsp;presenting this work to the public, is to impress upon geologists the advantage of attending more particularly to thenbsp;intimate organization of fossil plants; and should I succeed innbsp;directing their efforts towards the elucidation of this obscurenbsp;subject, I shall feel a degree of satisfaction which will amplynbsp;repay my labour�.�

On another page he writes as follows,��From investigations made by the most active and experienced botanical geologists, we find reason to conclude that the first appearance

Ettingshausen (79). Also numerous papers on fossil plants from Austria and other countries.

3 Sprengel (28). nbsp;nbsp;nbsp;^ Witham (33).nbsp;nbsp;nbsp;nbsp;� ibid., p. 3.

of an extensive vegetation occurred in the Carboniferous series ; and from a recent examination of the mountain-limestonenbsp;groups and coal-fields of Scotland, and the north of England,nbsp;we learn that these early vegetable productions, so far fromnbsp;being simple in their structure, as had been supposed, are asnbsp;complicated as the phanerogamic plants of the present day.nbsp;This discovery necessarily tends to destroy the once favouritenbsp;idea, that, from the oldest to the most recent strata, there hasnbsp;been a progressive development of vegetable and animal forms,nbsp;from the simplest to the most complex^� Since Witham�snbsp;day we have learnt much as to the morphology of Palaeozoicnbsp;plants, and can well understand the opinions to which he thusnbsp;gives expression.

It would be difficult to overrate the immense importance of this publication from the point of view of modern palaeobotany.

The art of making transparent sections of the tissues of fossil plants seems to have been first employed by Sanderson,nbsp;a lapidary, and it was afterwards considerably improved bynbsp;NicoP. This most important advance in methods of examination gave a new impetus to the subject, but it is somewhatnbsp;remarkable that the possibilities of the microscopical investigation of fossil plants have been but very imperfectly realisednbsp;by botanical workers until quite recent years. As regards suchnbsp;a flora as that of the Coal-Measures, we can endorse thenbsp;opinion expressed at the beginning of the century in referencenbsp;to the study of recent mosses�� Ohne das G�ttergeschenk desnbsp;zusammengesetzten Mikroskops ist auf diesem Felde durchausnbsp;keine Ernte�.� A useful summary of the history of the studynbsp;of internal structure is given by Knowlton in a memoirnbsp;published in 1889^ Not long after Witham�s book was issuednbsp;there appeared a work of exceptional merit by Corda�, in whichnbsp;numerous Palaeozoic plants are figured and fully described,nbsp;mainly from the standpoint of internal structure. This author

2 Nicol (34). See note by Prof. Jameson on p. 157 of the paper quoted, to the effect that he has long known of this method of preparing sections.

lays special stress on the importance of studying the microscopical structure of fossil plants.

well-known continental authors as Goppert, Cotta, Schimper, Stenzel, Schenk and a host of others, we may glance for anbsp;moment at the services rendered by English investigators tonbsp;the study of palaeobotanical histology. Unfortunately wenbsp;cannot always extend our examination of fossil plants beyondnbsp;the characters of external form and surface markings; but innbsp;a few districts there are preserved remnants of ancient floras innbsp;which fragments of stems, roots, leaves and other structuresnbsp;have been petrified in such a manner as to retain with wonderful completeness the minute structure of their internal tissues.nbsp;During the deposition of the coal seams in parts of Yorkshirenbsp;and Lancashire the conditions of fossilisation were exceptionally favourable, and thus English investigators have beennbsp;fortunately placed for conducting researches on the minutenbsp;anatomy of the Coal-Measure plants. The late Mr Binney ofnbsp;Manchester did excellent service by bis work on the internalnbsp;structure of some of the trees of the Coal Period forests. Innbsp;his introductory remarks to a monograph on the genusnbsp;Galamites, after speaking of the desirability of describingnbsp;our English specimens, he goes on to say, � When this isnbsp;done, we are likely to possess a literature on our Carboniferousnbsp;fossils worthy of the first coal-producing country^ The continuation and extension of Binney�s work in the hands ofnbsp;Carruthers, Williamson, and others, whose botanical qualifications enabled them to produce work of greater scientific value,nbsp;has gone far towards the fulfilment oi Binney s prophecy.

In dealing with the structure of Palaeozoic plants, we shall be Under constant obligation to the splendid series of memoirsnbsp;from the pen of Prof. Williamson^. As the writer of anbsp;sympathetic obituary notice has well said; � In his fifty-fifthnbsp;year he began the great series of memoirs which mark thenbsp;culminating point of his scientific activity, and which willnbsp;assure to him, for all time, in conjunction with Brongniart, the

honourable title of a founder of modern Palaeobotany'.� If we look back through a few decades, and peruse the pages of Lindleynbsp;and Hutton�s classic work^ on the Fossil flora of Great Britain,nbsp;a book which is indispensable to fossil botanists, and read thenbsp;description of such a genus as Sigillaria or Stigmaria; or if wenbsp;extend our retrospect to an earlier period and read Woodward�snbsp;description of an unusually good specimen of a Lepidodendron,nbsp;and Anally take stock of our present knowledge of such plants,nbsp;we realise what enormous progress has been made in palaeo-botanical studies. Lindley and Hutton, in the preface to thenbsp;first volume of the Flora, claim to have demonstrated that bothnbsp;Sigillaria and Stigmaria were plants with � the highest degreenbsp;of organization, such as Gactaeae, or Euphorbiaceae, or evennbsp;Asclepiadeae�; Woodward describes his Lepidodendron (Fig. 1) asnbsp;� an ironstone, black and flat, and wrought over one surface verynbsp;finely, with a strange cancellated work�.� Thanks largely to

the work of Binney, Carruthers, Hooker, Williamson, and to the labours of continental botanists, we are at present almost asnbsp;familiar with Lepidodendron and several other Coal-Measure

genera as with the structure of a recent forest ree. , emphasizing the value of the microscopic metho s o invesnbsp;tion, we are not disposed to take such a hopeless view onbsp;possibilities of the determination of fossil forms, m w icnbsp;internal structure is preserved, as some writers have �nbsp;nbsp;nbsp;nbsp;,

The preservation of minute structure is to be grea y ^ from the point of view of the modern palaeobotarns , unbsp;must recognise the necessity of making such use as enbsp;the numberless examples of plants of all ages, whic ocnbsp;in the form of structureless casts or impressions. ^

In looking through the writings of the earlier au cannot help noticing their anxiety to match all fossi p an snbsp;living species; but by degrees it was discovered t at oss ^nbsp;frequently the fragmentary samples of extinct types, wnbsp;be studied only under very unfavourable conditions. ^ .nbsp;absence of those characters on which the student^ onbsp;plants relies as guides to classification, it is usuallynbsp;nbsp;nbsp;nbsp;.

to arrive at any trustworthy conclusions as to precise � ^ affinity. Brongniart and other authors recognise ^nbsp;nbsp;nbsp;nbsp;^ �

and instituted several convenient generic terms o a pure y artificial and provisional nature, which are still in genera inbsp;The dangers and risks of error which necessarily attennbsp;attempts to determine small and imperfect fragments o exnbsp;species of plants, will be briefly touched on in anot er p

CHAPTER II.

� La recherche du plan de la creation, voila le but vers lequel nos efforts peuvent tendre aujourd�hui.� Gaudey, 1883.

Singe the greater refinements and thoroughness of scientific methods and the enormous and ever-increasing mass of literaturenbsp;have inevitably led to extreme specialisation, it is more thannbsp;ever important to look beyond the immediate limits of one�snbsp;own subject, and to note its points of contact with other linesnbsp;of research. A palaeobotanist is primarily concerned with thenbsp;determination and description of fossil plants, but he must atnbsp;the same time constantly keep in view the bearing of his worknbsp;on wider questions of botanical or geological importance. Fromnbsp;the nature of the case, we have in due measure to adapt thenbsp;methods of work to the particular conditions before us. It isnbsp;impossible to follow in the case of all fossil species precisely thenbsp;same treatment as with the more complete and perfect recentnbsp;plants; but it is of the utmost importance for a student ofnbsp;palaeobotany, by adhering to the methods of recent botany, tonbsp;preserve as far as he is able the continuity of the past andnbsp;present floras. Palaeontological work has often been undertakennbsp;by men who are pure geologists, and whose knowledge of zoologynbsp;or botany is of the most superficial character, with the resultnbsp;that biologists have not been able to avail themselves, to anynbsp;considerable extent, of the records of extinct forms of life.

division has been made between the science of the g world of to-day and that of the past.nbsp;nbsp;nbsp;nbsp;f/poloeist

round the relics of ancient floras, hr � �Uprstand how-fore, with fixing the age of strata, it is easy^o u^^^ p^^laeon-geologists have been content -with a sp , nbsp;nbsp;nbsp;, f systematic

botany. It would seem, then, that the ��^inTarge or comparative neglect otnbsp;nbsp;nbsp;nbsp;too often charoo-

and has resulted in a one-sided ami, sundpoint, unscientific treatment of this br.noh of somo

brought the subject into disiepute by nbsp;nbsp;nbsp;.nbsp;nbsp;nbsp;nbsp;. �Ug im-

specimens, and the practice of drawing cone us �morally tanical affinity without any trustworthy evidence, ^ave jturffilynbsp;given rise to considerable scepticism as to e vanbsp;botanical records. Another point, which wi 1 he � ^

geological age; this again, is no doubt to a large extent the result of imperfect and inaccurate methods of description, andnbsp;of the neglect of and consequent imperfect acquaintance withnbsp;fossil plants as compared with fossil animals.

The student of fossil plants should endeavour to keep before him the fact that the chief object of his work is to deal with thenbsp;available material in the most natural and scientific manner; andnbsp;by adopting the methods of modern botany, he should always aimnbsp;to follow such lines as may best preserve the continuity of pastnbsp;and present types of plants. Descriptions of floras of past agesnbsp;and lists of fossil species, should be so compiled that they maynbsp;serve the same purpose to a stratigraphical geologist, who isnbsp;practically a geographer of former periods of the Earth�s history,nbsp;as the accounts of existing floras to students of present daynbsp;physiography. The effect of carrying out researches on somenbsp;such lines as these, should be to render available to bothnbsp;botanists and geologists the results of the specialist�s work.

In some cases, palaeobotanical investigations may be of the utmost service to botanical science, and of little or no value tonbsp;geology. The discovery of a completely preserved gametophytenbsp;of Lepidodendron or Calamites, or of a petrified Moss plant innbsp;Palaeozoic rocks would appeal to most botanists as a matter ofnbsp;primary importance, but for the stratigraphical geologist suchnbsp;discoveries would possess but little value. On the other handnbsp;the discovery of some characteristic species of Coal-Measurenbsp;plants from a deep boring through Mesozoic or Tertiary stratanbsp;might be a matter of special geological importance, but to thenbsp;botanist it would be of no scientific value. In very manynbsp;instances, however, if the palaeobotanist follows such lines asnbsp;have been briefly suggested, the results of his labours should benbsp;at once useful and readily accessible to botanists and geologists.nbsp;As Humboldt has said in speaking of Palaeontology, �thenbsp;analytical study of primitive animal and vegetable life hasnbsp;taken a double direction; the one is purely morphological, andnbsp;embraces especially the natural history and physiology ofnbsp;organisms, filling up the chasms in the series of still livingnbsp;species by the fossil structures of the primitive world. Thenbsp;second is more specially geognostic, considering fossil remains

in their relations to the superposition and relative age of the sedimentary formationsh�

To turn for a moment to some of the most obvious connections between palaeobotany and the wider sciences of botany and geology. The records of fossil species must occupy anbsp;prominent position in the data by which we may hope to solvenbsp;some at least of the problems of plant evolution. From thenbsp;point of view of distribution, palaeobotany is of considerablenbsp;value, not only to the student of geographical botany, but tonbsp;the geologist, who endeavours to map out the positions ofnbsp;ancient continents with the help of palaeontological evidence.nbsp;The present distribution of plants and animals represents butnbsp;one chapter in the history of life on the Earth; and to understand or appreciate the facts which it records, we have to looknbsp;back through such pages as have been deciphered in the earliernbsp;chapters of the volume. The distribution of fossil plants liesnbsp;at the foundation of the principles of the present grouping ofnbsp;floras on the Earth�s surface. Those who have confined their studynbsp;of distribution to the plant geography of the present age, mustnbsp;Supplement their investigations by reference to the work ofnbsp;palaeohotanical writers. If the lists of plant species drawn upnbsp;fly specialists in fossil botany, have been prepared with a duenbsp;Sense of the important conclusions which botanists may drawnbsp;from them from .the standpoint of distribution, they will benbsp;readily accepted as sound links in the chain of evidence.nbsp;Unfortunately, however, if many of the lists of ancient florasnbsp;were made use of in such investigations, the conclusions arrivednbsp;at Would frequently be of little value on account of the untrustworthy determinations of many of the species. In the casenbsp;cf particular genera the study of the distribution of the formernbsp;species both in time and space, that is geologically and geographically, points to rational explanations of, or gives addednbsp;significance to, the facts of present day distribution. Thatnbsp;isolated conifer, Ginkgo biloba L. now restricted to Japannbsp;and China, was in former times abundant in Europe andnbsp;in other parts of the world. It is clearly an exceedingly ancientnbsp;fyp�, isolated not only in geographical distribution but innbsp;1 Humboldt (48), vol. i. p. 274.

botanical affinities, which has reached the last stage in its natural life. The Mammoth trees of California {Sequoia sempervirensnbsp;Endl., and S. gigantea Lindl. and Gord.) afford other examples of anbsp;parallel case. The North American Tulip tree and other alliednbsp;forms are fairly common in the Tertiary plant beds of Europe, butnbsp;the living representatives are now exclusively North American.nbsp;Such differences in distribution as are illustrated by thesenbsp;dicotyledonous forest trees in Tertiary times and at the presentnbsp;day, have been clearly explained with the help of the geologicalnbsp;record. Forbes, Darwin, Asa Gray' and others have been ablenbsp;to explain many apparent anomalies in the distribution ofnbsp;existing plants, and to reconcile the differences between thenbsp;past and present distribution of many genera by taking accountnbsp;of the effect on plant life of the glacial period. As the icenbsp;gradually crept down from the polar regions and spread over thenbsp;northern parts of Europe, many plants were driven further southnbsp;in search of the necessary warmth. In the American continentnbsp;such migration was rendered possible by the southern landnbsp;extension; in Europe on the other hand the southerly retreatnbsp;was cut off by impassable barriers, and the extinction of severalnbsp;genera was the natural result.

The comparatively abundant information which we possess as to the past vegetation of polar regions and the value of suchnbsp;knowledge to geologists and botanists alike is in strikingnbsp;contrast to the absence of similar data as regards Antarcticnbsp;fossils. Darwin in an exceedingly interesting letter to Hookernbsp;a propos of a forthcoming British Association address, referringnbsp;to this subject writes as follows:�

� The extreme importance of the Arctic fossil plants is self-evident. Take the opportunity of groaning over our ignorance of the Lignite plants of Kerguelen Land, or any Antarctic land.nbsp;It might do good

In working out any collection of fossil plants, it would be well, therefore, to bear in mind that our aim should be rathernbsp;to reproduce an accurate fragment of botanical history, than to

' Vide Hooker, J. D. (81), for references to other writers on this subject; also Darwin (82), ch. xii.

perform feats of determination with hopelessly inadequate specimens. Had this principle been generally followed, thenbsp;number of fossil plant species would be enormously reduced,nbsp;but the value of the records would be considerably raised.

Onr knowledge of plant anatomy, and of those laws of growth which govern certain classes of plants to-day and innbsp;past time, has been very materially widened and extended b}nbsp;the facts revealed to us by the detailed study of Coal-Measurenbsp;species. The modern science of Plant Biology, refoundednbsp;hy Charles Darwin, has thrown considerable light on thenbsp;laws of plant life, and it enables us to correlate structuralnbsp;characteristics with physiological conditions of growth. Applying the knowledge gained from living plants to the study ofnbsp;such extinct types as permit of close microscopic examinatfon,nbsp;we may obtain a glimpse into the secrets of the botanicalnbsp;hinomics of Palaeozoic times. The wider questions of climaticnbsp;conditions depend very largely upon the evidence of fossilnbsp;botany for a rational solution. As an instance of jihe bestnbsp;authenticated and most striking alternation in climatic conditions in comparatively recent times, we may cite the glacialnbsp;period or Ice-Age. The existence of Arctic conditions hasnbsp;been proved by purely geological evidence, but it receivesnbsp;additional confirmation, and derives a wider importance fromnbsp;the testimony of fossil plants. In rocks deposited before thenbsp;spread of ice from high northern latitudes, we find indubitablenbsp;proofs of a widely distributed subtropical flora in Central andnbsp;Northern Europe. Passing from these rocks to more recentnbsp;beds there are found indications of a fall in temperature, andnbsp;such northern plants as the dwarf Birch, the Arctic Willow

senes of strata which make up the crust of the earth i ^ matter of primary importance from a botanica as wenbsp;a geological point of view.nbsp;nbsp;nbsp;nbsp;.nbsp;nbsp;nbsp;nbsp;, marked

to correlate the periods of maximum development of certain classes of plants with definite epochs of geological history. Henbsp;gives the following classification in which are represented thenbsp;general outlines of plant development from Palaeozoic tonbsp;Tertiary times h

Since Brongniart�s time this method of classification has been extended to many of the smaller subdivisions of thenbsp;geological epochs, and species of fossil plants are often of thenbsp;greatest value in questions of correlation. In recent years thenbsp;systematic treatment of Coal-Measure and other plants in thenbsp;hands of various Continental and English writers has clearlynbsp;demonstrated their capabilities for the purpose of subdividingnbsp;a series of strata into stages and zones The more completenbsp;becomes our knowledge of any flora, the greater possibilitynbsp;there is of making use of the plants as indices of geologicalnbsp;age I

Not only is it possible to derive valuable aid in the correlation of strata from the facts of plant distribution, but we may often follow the various stages in the history of a particularnbsp;genus as we trace the records of its occurrence through thenbsp;geologic series. In studying the march of plant life throughnbsp;past ages, the botanist may sometimes follow the progress of anbsp;genus from its first appearance, through the time of maximumnbsp;development, to its decline or extinction. In the Palaeozoicnbsp;forests there was perhaps no more conspicuous or common treenbsp;than the genus long known under the name of Calamites.

enabled �e b� become almost -tml-structure of their stems and roots, as nbsp;nbsp;nbsp;��ips In

short, it .s thorougUj established that C�!a�.t� �g-�' essential respects with onr well known Equisetum, anbsp;included in the same order, or at least suh-c ass,

genus of Equisetaceae. As we ascend the geo 0^,10 nbsp;nbsp;nbsp;� ,nbsp;nbsp;nbsp;nbsp;^

of the Vosges, which belong to the same senes o r . Triassic strata of the Cheshire plain, the true anbsp;replaced by a large Equisetum apparently identica mnbsp;appearance and habit of growth with thenbsp;nbsp;nbsp;nbsp;a (j

period forests. The pages of such a history are freque y imperfect and occasionally missing, but others, agai , ^nbsp;written in characters as clear as those- which we ^ ecip

As one of the most striking instances in which t e scopic study of fossil plants has shown the way 0nbsp;satisfactory solution of the problems of development ve maynbsp;mention such extinct genera as Lyginodendr on, ^ ye oxy 0nbsp;and others. Each of these genera will be dealt wit a soinbsp;length in the systematic part of the hook, an we

afterwards discuss the importance of such types, from the point of view of plant evolution.

The botanist who would trace out the phylogeny of any existing class or family, makes it his chief aim to discovernbsp;points of contact between the particular type of structurenbsp;which he is investigating, and that of other more or less closelynbsp;related classes or families.

Confining himself to recent forms, he may discover, here and there, certain anatomical or embryological facts, which suggestnbsp;promising lines of inquiry in the quest after such affinities asnbsp;point to a common descent. Without recourse to the evidencenbsp;afforded by the plants of past ages, we must always admit thatnbsp;our existing classification of the vegetable kingdom is an expression of real gaps which separate the several classes of plantsnbsp;from one another. On the other hand our recently acquirednbsp;and more accurate knowledge of such genera as have beennbsp;alluded to, has made us acquainted with types of plantnbsp;structure which enable us to fill in some of the lacunae in ournbsp;existing classification. In certain instances we find merged innbsp;a single species morphological characteristics which, in the casenbsp;of recent plants, are regarded as distinctive features of differentnbsp;sub-divisions. It has been clearly demonstrated that innbsp;Lyginodendron, we have anatomical peculiarities typical ofnbsp;recent cycads, combined with structural characteristics alwaysnbsp;associated with existing ferns. In rare cases, it happens thatnbsp;the remarkably perfect fossilisation of the tissues of fossilnbsp;plants, enables us not only to give a complete description ofnbsp;the histology of extinct forms, but also to speak with confidence as to some of those physiological processes whichnbsp;governed their life.

So far, palaeobotany has been considered in its bearings on the study of recent plants. From a geological point of viewnbsp;the records of ancient floras have scarcely less importance. Innbsp;recent years, facts have been brought to light, which shownbsp;that plants have played a more conspicuous part than hasnbsp;usually been supposed as agents of rock-building. As tests ofnbsp;geologic age, there are good grounds for believing that thenbsp;inferiority of plants to animals is more apparent than real.

Enough has been said to show the many-sided nature of the science of Fossil Plants, and the wide range of the problemsnbsp;which the geologist or botanist may reasonably expect to solve,nbsp;by means of trustworthy^ data afforded by scientific palaeo-

CHAPTER HL

In attempting to sketch in briefest outline the geological history of the Earth, the most important object to keep innbsp;view is that of i-eproducing as far as possible the broadnbsp;features of the successive stages in the building of the Earth�snbsp;crust. It is obviously impossible to'go into any details ofnbsp;description, or to closely follow the evolution of the presentnbsp;continents; at most, we can only refer to such facts as maynbsp;serve as an introduction of the elements of stratigraphicalnbsp;geology to non-geological readers. For a fuller treatment ofnbsp;the subject reference must be made to special treatises onnbsp;geology.

For the sake of convenience, it is customary in stratigraphical geology as also in biology, to make use of our imperfect knowledge as an aid to classification. If we possessednbsp;complete records of the Earth�s history, we should have annbsp;unbroken sequence, not merely of the various forms of lifenbsp;that ever existed, but of the different kinds of rocks formednbsp;in the successive ages of past time. As gaps exist in thenbsp;chain of life, so also do we find considerable breaks in thenbsp;sequence of strata which have been formed since the beginningnbsp;of geologic time. The danger as well as the convenience ofnbsp;artificial classification must be kept in view. This has been

* Old Persian writer, quoted by E. G. Browne in A Year among the Persians, p. 220, London, 1893.

well expressed by Freeman, in speaking of architectural styles,�� Our minds,� he says, � are more used to definitenbsp;periods; they neglect or forget transitions which do indeednbsp;exist. Thg idea of definite classification is liable to narrow

ipoBing that part of the earth whmh is us,�or as it is generally called the earths cius ,nbsp;nbsp;nbsp;nbsp;^

rocks of various kinds, of which some have ee igneous agency, either as lavas or beds o as ,nbsp;form of molten magmas which gradually coo �nbsp;crystalline below a mass of superincumbent s ranbsp;these rocks we need not concern ourselves. _

�hich ha,o been formed in preoisely the same deposits are being accumulated at thenbsp;nbsp;nbsp;nbsp;the

action of destructive agencies, and suffers perpe ua is the products of this ceaseless wear and tearnbsp;building materials of new deposits.nbsp;nbsp;nbsp;nbsp;wind

changes of temperature, and other agents o cannot be fully dealt with in this short summaiy. � i j

later, as the rate of flow slackens, it deposits e m in the river-bed or on the floor of the sea or a .

material became cemented together either action of some solution percolatingnbsp;mass, or by the pressure of overlyingnbsp;W. E. W. Stephens, Life of Freeman, p. 132, London, 1895.

deposits, there would be formed a hard rock made up of rounded fragments of various kinds of strata derived fromnbsp;different sources. Such a rock is known as a Conglomerate.nbsp;The same kind of rock may be formed equally well by thenbsp;action of the sea; an old sea-beach with the pebbles embeddednbsp;in a cementing matrix affords a typical example of a coarsenbsp;conglomerate. Plant remains ar^ occasionally met with innbsp;conglomerates, but usually in a fragmentary condition.

From a conglomerate composed of large water-worn pebbles, to a fine homogeneous sandstone there are numerous intermediate stages. A body of water, with a velocity too small tonbsp;carry along pebbles of rock in suspension or to roll them along thenbsp;bed of the channel, is still able to transport the finer fragmentsnbsp;or grains of sand, but as a further decrease in the velocitynbsp;occurs, these are eventually deposited as beds of coarse or finenbsp;sand. The stretches of sand on a gradually shelving sea shore,nbsp;or the deposits of the same material in a river�s delta, havenbsp;been formed by the gradual wearing away and disintegrationnbsp;of various rocks, the detritus of which has been spread out innbsp;more or less regular beds on the floor of a lake or sea.nbsp;Such accumulations of fine detrital material, if compactednbsp;or cemented together, become typical Sandstones.

In tracing beds of sandstone across a tract of country, it is frequently found that the character of the strata graduallynbsp;alters; mud or clay becomes associated with the sandy deposit,nbsp;until finally the sandstone is replaced by beds of dark colourednbsp;shale. Similarly the sandy detritus on the ocean floor, or innbsp;an inland lake, when followed further and further from thenbsp;source from which the materials were derived, passes bvnbsp;degrees into argillaceous sand, and finally into sheets of darknbsp;clay or mud. The hardened beds of clay or fine grained mudnbsp;become transformed into Shales. As a general rule, then,nbsp;shales are rocks which have been laid down in places furthernbsp;from the land, or at a greater distance from the source ofnbsp;origin of the detrital material, than sandstones or conglomerates.nbsp;The conglomerates, or old shingle beaches, usually occur innbsp;somewhat irregular patches, marking old shore-lines or thenbsp;head of a river delta. Coarse sandstones, or grits, may occur

in the form of regularly bedded strata stretching ., y area; and shales or clays may be followed through anbsp;extent of country. The finer material composing the ^nbsp;and shales has been held longer in suspension an

resemblance of such deposits to modern deseit a similar method of formation; and there can be �nbsp;in some instances there have beennbsp;nbsp;nbsp;nbsp;accumn-

lations, although by no means common, are of sufhci ance to be mentioned as illustrating a certain typenbsp;nbsp;nbsp;nbsp;�nbsp;nbsp;nbsp;nbsp;^

The thick masses of limestone which form so p a feature in parts of England and Ireland, ave �nbsp;in a manner different from that to wbic san snbsp;shales owe their origin. On the floor of a c ear se �nbsp;nbsp;nbsp;nbsp;^

as ebalk or LmESTONI. Tgt;'�f �8�� t by calcareous which are enclosed either wholly or m p J ,nbsp;nbsp;nbsp;nbsp;.1,,

Not a few limestones consist in part of ossi co , owe their origin to colonies of coral polyps w icnbsp;reefs or hanks of coral in the ancient seas.nbsp;nbsp;nbsp;nbsp;j j

In the white cliffs of Dover, Flamboroiigh Head and other places, we have a somewhat different form o ca careo

which in part consists of millions of minute shells of Fora-minifera, in part of broken fragments of larger shells of extinct molluscs, and to some extent of the remains of siliceous sponges.nbsp;As a general rule, limestones and chalk rocks are ancient sediments, formed in clear and comparatively deep water, composednbsp;in the main of carbonate of lime, in some cases with a certainnbsp;amount of carbonate of magnesium, and occasionally with anbsp;considerable admixture of silica.

In such rocks land-plants must necessarily he rare. There are, however, limestones which wholly or in part owe theirnbsp;formation to masses of calcareous algae, which grew in thenbsp;form of submarine banks or on coral reefs. Occasionally thenbsp;remains of these algae are clearly preserved, but frequentlynbsp;all signs of plant structure have been completely obliterated.nbsp;Again, there occur limestone rocks formed by chemical means,nbsp;and in a manner similar to that in which beds of travertine arenbsp;now being accumulated.

Granites, basalts, volcanic lavas, tuffs, and other igneous rocks need not claim our attention, except in such cases asnbsp;permit of plant remains being found in association with thesenbsp;materials. Showers of ashes blown from a volcano, may fallnbsp;on the surface of a lake or sea and become mixed with sandnbsp;and mud of subaerial origin. Streams of lava occasionallynbsp;flow into water, or they may be poured from submarine vents,nbsp;and so spread out on the ocean bed with strata of sand or cla}'.

Passing from the nature and mode of origin of the sedimentary strata to the manner of their arrangement innbsp;the Earth�s crust, we must endeavour to sketch in the merestnbsp;outline the methods of stratigraphical geology. The surfacenbsp;of the Earth in some places stands out in the form of barenbsp;masses of rock, roughly hewn or flnely carved by Nature�snbsp;tools of frost, rain or running water; in other places we havenbsp;gently undulating ground with beds of rock exposed to viewnbsp;here and there, but for the most part covered with loosenbsp;material such as gravel, sands, boulder clay and surface soil.

In the flat lands of the fen districts, the peat beds and low-lying salt marshes form the surface features, and are thenbsp;connecting links between the rock-building now in progress and

t�ie deposits of an earlier age. If we could remove all these ^^^'itH'iIations of sand, gravel, peat and surface soil,nbsp;take a bird�s eye view of the bare surface of the rockynbsp;\nbsp;nbsp;nbsp;nbsp;earth�s crust, we should have spread before

ho � ^ ^�^tlines of a geological map. In some places fairly zontal beds of rock stretching over a wide extent ofnbsp;country^ in another the upturned edges of almost verticalnbsp;the surface features; or, again, irregular bosses ofnbsp;^^ystalline igneous rock occur here and there as patches innbsp;midst of bedded sedimentary or volcanic strata. A mapnbsp;ing the boundaries and distribution of the rocks as seennbsp;e surface, tells us comparatively little as to the relativenbsp;positions of the different rocks below ground, or of the relativenbsp;^��08 of the several strata. If we supplement this superficialnbsp;oy an inspection of the position of the strata as shown onnbsp;� ^^lls of a deep trench cut across the country, we at oncenbsp;gain very important information as to the relative position of thenbsp;s below the earth�s surface. The face of a quarry, the sidenbsp;bed or a railway cutting, afford horizontal sectionsnbsp;bel^^^^^^^* ^^bich show whether certain strata lie above ornbsp;others, whether a series of rocks consists of parallel andnbsp;� arly stratified beds, or whether the succes.sion of the stratanbsp;quot; ^^^tsrfered with by a greater or less divergence from a parallelnbsp;^Tiangeixien^;_ If for example, a section shows comparativelynbsp;^^iizontal strata lying across the worn down edges of a seriesnbsp;'�ftrtical sedimentary rocks, we may fairly assume thatnbsp;such changes as the following have taken place in that

less h ^ .'^�^quot;�rlying beds were originally laid down as more or orizontal deposits; these were gradually hardened andnbsp;elevated above sea-level by a folding of thenbsp;s crust; the crests of the folds were afterwards worn downnbsp;Sea.,nbsp;nbsp;nbsp;nbsp;the eroded surface finally subsided below

ar k Such breaks in the continuity of stratified deposits iiown as UNCONFORMITIES; in the interval of time whichnbsp;y represent great changes took place of which the recordsnbsp;either entirely lost, or have to be sought elsewhere.

In certain more exceptional cases, it is possible to obtain what is technically known as a vertical section ; for examplenbsp;if a deep boring is sunk through a series of rocks, and thenbsp;core of the boring examined, we have as it were a sample ofnbsp;the earth�s crust which may often teach us valuable lessonsnbsp;which cannot be learnt from maps or horizontal sections.

It is obvious, that in a given series of beds, which are either horizontal or more or less obliquely inclined, thenbsp;underlying strata were the first formed, and the upper bedsnbsp;were laid down afterwards. If, however, we trusted solely tonbsp;the order of superposition in estimating relative age, our conclusions would sometimes benbsp;nbsp;nbsp;nbsp;verynbsp;nbsp;nbsp;nbsp;far fromnbsp;nbsp;nbsp;nbsp;thenbsp;nbsp;nbsp;nbsp;truth.

Recent geological investigations nbsp;nbsp;nbsp;havenbsp;nbsp;nbsp;nbsp;brought to light facts

well nigh incredible as to the magnitude and extent of rock-foldings. In regions of great earth-movements, the crust has been broken along certain lines, and great masses of stratanbsp;have been thrust for miles along the tops of newer rocks.nbsp;Thus it may be brought about that the natural sequence of anbsp;set of beds has been entirely altered, and older rocks havenbsp;come to overlie sediments of anbsp;nbsp;nbsp;nbsp;laternbsp;nbsp;nbsp;nbsp;geologicalnbsp;nbsp;nbsp;nbsp;age.nbsp;nbsp;nbsp;nbsp;Facts

such as these clearly illustrate nbsp;nbsp;nbsp;thenbsp;nbsp;nbsp;nbsp;difficultiesnbsp;nbsp;nbsp;nbsp;ofnbsp;nbsp;nbsp;nbsp;correct

In the horizontal section (Fig. 2), from the summit of B�zi-stock on the left to Saasterg on the right, we have a striking case of intense rock-folding and dislocation h Prof. Heim^ of Genevanbsp;has given numerous illustrations of the almost incrediblenbsp;positions assumed in the Swiss Mountains by vast thicknessesnbsp;of rocks, and in the accompanjdng section taken from a recentnbsp;work by Rothpletz we have a compact example of the possibilities of earth-movements as an agent of rock-folding. Thenbsp;section illustrates v^ery clearly an exception to the rule that thenbsp;order of superposition of a set of beds indicates the relative agenbsp;of the strata. The horizontal line at the base is drawn atnbsp;a height of 1650 metres above sea-level, and the summit ofnbsp;B�zistock reaches a height of 2340 m. The youngest rocksnbsp;seen in the diagram are the Eocene beds e, at the base and asnbsp;small isolated patches on the right-hand end of the section;

the main mass of material composing the higher ground has been bodily thrust over the Eocene rocks, and in this processnbsp;some of the beds, 6 and c, have been folded repeatedly on them-

];'A:

folding, as such phenomena are by no means exceptional in many parts of the ^Yorld.

The order of superposition of strata has afforded the key to our knowledge of the succession of life in geologic time, and thenbsp;refinements of the stratigraphical correlation of sedimentarynbsp;rocks are based on the comparison of their fossil contents. Bynbsp;a careful examination of the relics of fossil organisms obtainednbsp;from rocks of all ages and countries, it has been found possiblenbsp;to restore in broken outline the past history of the Earth.nbsp;By means, then, of stratigraphical and palaeontological evidence,nbsp;a classification of the various rocks has been established, thenbsp;lines of division being drawn in such places as represent gapsnbsp;in the fossil records, or striking and widespread unconformitiesnbsp;between different series of deposits.

It is only in a few regions that we find rocks which can reasonably be regarded as the foundation stones of the Earth.nbsp;As the globe gradually cooled, and its molten mass becamenbsp;skinned over with a solid crust, crystalline rocks must havenbsp;been produced before the dawn of life, and before water couldnbsp;remain in a liquid form on the rocky surface. As soon as tlienbsp;temperature became sufficiently low, running water and rainnbsp;began the work of denudation and rock disintegration whichnbsp;has been ceaselessly carried on ever since. In this continualnbsp;breaking down and building up of the Earth�s surface, it wouldnbsp;be no wonder if but few remnants were left of the first formednbsp;sediments of the earliest age.

The action of heat, pressure and chemical change accompanying rock-foldings and crust-wrinklings, often so far alters sedimentary deposits, that their original form is entirely lost,nbsp;and sandstone, shales and limestones become metamorphosednbsp;into crystalline quartzites, slates and marbles.

The operation of metamorphism is therefore another serious difficulty in the way of recognising the oldest rocks. Thenbsp;earliest animals and plants which have been discovered arenbsp;not such as we should expect to find as examples of the firstnbsp;products of organic life. Below the oldest known fossiliferousnbsp;rocks, there must have been thousands of feet of sedimentarynbsp;material, which has either been altered beyond recognition, or

a general introduction to geological chronology, a short summary niay be given of the different formations or groups ofnbsp;I'a a, to which certain names have been assigned to serve asnbsp;convenient designations for succeeding epochs in the world�snbsp;thenbsp;nbsp;nbsp;nbsp;following table (Fig. S, pp. 32, 33) represents

shad'^*^�^^ each period are indicated by the usual conventional lug, and the most important breaks or lacunae in the recordsnbsp;are shown by gaps and uneven lines. The relative thicknessnbsp;e rocks of each period is approximately shown; but thenbsp;^eitical extent of the oldest or Archaean rocks as shown innbsp;ig_- 3 represents what is without doubt but a fraction ofnbsp;eir proportional thickness. This table is taken, with certainnbsp;_ ciations, from a paper by Prof. T. McKenny Hughes in thenbsp;Philosophical Proceedings for 1879. Speakingnbsp;e graphic method of showing the geological series,nbsp;tabl^'^^^*^^nbsp;nbsp;nbsp;nbsp;paper says, �It is convenient to have a

rocks of the world in parallel columns, and say that ABC stilH^ ^1�� exactly synchronous with A'B'C of another,nbsp;we fi^nbsp;nbsp;nbsp;nbsp;couiitry and establish a grouping for it,

entified in distant places, that we generally make an conv^^�^^^^'^ homotaxis as Huxley called it. The most

obviously to bracket together locally froinbsp;nbsp;nbsp;nbsp;i.e. all the sediment which was formed

hewan ^ when the land went down and accumulation work*^' f �nbsp;nbsp;nbsp;nbsp;time when the sea bottom was raised and the

bear^ ^ of Great Britain classified on this system, and by d^'^^ �iud that waste in one place must be represented

on y intervals estimated where possible by the amount of u ation known to have taken place between the periods ofnbsp;fleposition in the same districts

Lavas, Volcanicnbsp;Ashes,nbsp;Granitoidnbsp;Locks andnbsp;Schists opnbsp;Enormousnbsp;Thickness

There is perhaps no problem at once so difficult and so full of interest to the student of the Earth�s history, as the interpretation of the fragmentary records of the opening stages innbsp;g�|Ological and organic evolution. In tracing the growth andnbsp;development of the human race, it becomes increasinglynbsp;difficult to discover and decipher written documents as wenbsp;penetrate farther back towards the beginning of the historicalnbsp;period; the records are usually incomplete and fragmentary, ornbsp;rendered illegible by the superposed writings of a later date. Sonbsp;in the records of the rocks, as we pass beyond the oldest strata innbsp;which clearly preserved fossils are met with, we come to oldernbsp;rocks which afford either no data as to the period in which theynbsp;were formed, or like the palimpsest, with its original charactersnbsp;almost obliterated by a late MS., the older portions of thenbsp;Earth�s crust have been used and re-used in the rock-buildingnbsp;of later ages. In the first place, it is exceedingly difficult tonbsp;determine with any certainty what rocks may be regarded asnbsp;trustworthy fragments of a primaeval land. Throughout thenbsp;geological eras the Earth�s surface has been subjected tonbsp;foldings and wrinklings, volcanic activity has been almostnbsp;unceasing, and there is abundant evidence to show how thenbsp;original characters of both igneous and sedimentary rocks maynbsp;be entirely effaced by the operation of chemical and physicalnbsp;forces. It was formerly held that coarsely crystalline rocksnbsp;such as granite are the oldest portions of the crust, butnbsp;modern geology has conclusively proved that many of thenbsp;so-called fundamental masses of rock are merely piles of ancientnbsp;sediments which have been subjected to the repeated operationnbsp;of powerful physical and chemical forces, and have undergone anbsp;complete rearrangement of their substance. As the result ofnbsp;more detailed investigations, many regions formerly supposednbsp;to consist of the foundation stones of the Earth�s crust, arenbsp;now known to have been centres of volcanic disturbance and

would entirely cover up portions of t o There is reason to their turn succeeded by still later deposi s.nbsp;nbsp;nbsp;nbsp;history, the

believe that in the remotest ages o o ijlere more potent forces of denudation and igneousnbsp;nbsp;nbsp;nbsp;5'nbsp;nbsp;nbsp;nbsp;, could hardly

retain their original structure tmo g ��o-Auio life were geologic W. The eeriieetnbsp;nbsp;nbsp;nbsp;fte� �� 'lt;*

igneous eruptions, the relics o� life �f ,'gt;*?*�; LgL..� of It is, in short, practically hopeless to looknbsp;nbsp;nbsp;nbsp;,on-

the primitive crust except such as �-J�search for any siderable metamorphism, and equally m

as granite, but differing in the regular constituent parts. To such rocks the terms gneis

have been applied. Bocks of this kind are y no � consist of Archaean age, but many of tbe earliestnbsp;nbsp;nbsp;nbsp;^avas,

Director of the Canadian Geological Survey applied the term Laurentian. These Laurentian rocks, with similar strata innbsp;Scandinavia, the north-west Highlands of Scotland, in certainnbsp;parts of such mountain ranges as the Alps, Pyrenees, Carpathians, Himalayas, Andes, Atlas, amp;c., have been classednbsp;together as members of the oldest geological period, and arenbsp;usually referred to under the name of Archaean, or lessnbsp;frequently Azoic rocks. In some of the uppermost Archaeannbsp;rocks there have been recently discovered a few undoubtednbsp;traces of fossil animals, but with this exception no fossils arenbsp;known throughout the great mass of Archaean strata. It isnbsp;true that some authorities regard the beds of graphite andnbsp;other rocks as a proof of the abundance of plant life, but thisnbsp;supposition is not supported by any convincing evidence.

The term Azoic ^ applied by some writers to these oldest rocks suggests the absence of life during the period in whichnbsp;they were formed. Life there must have been, though we arenbsp;unable to discover its records. The period of time representednbsp;by the Archaean or Pre-Cambrian rocks must be enormous,,nbsp;and it was in that earliest era that the first links in the chainnbsp;of life were forged.

II. Cambrian.

The term Cambrian was adopted by Sedgwick for a series of sedimentary rocks in North Wales {Cambria). In thatnbsp;district, in South Wales, the Longmynd Hills, the Malverns,,nbsp;in Scotland, and other regions there occur more or less highlynbsp;folded and contorted beds of pebbly conglomerate, sandstones,nbsp;shales and slates resting on the uneven surface of an Archaeannbsp;foundation.

It is in these Cambrian rocks that trustworthy records of organic life are first met with. Among the most constantnbsp;and characteristic fossils of this period are the extinct andnbsp;aberrant members of the crustacea, the trilobites; these withnbsp;some brachiopods, sponges,^ and other fossils comprise the

oldest fauna, of which the ancestral types have yet to he discovered. During the last few decades the number ofnbsp;Cambrian fossils has been considerably increased, and innbsp;�certain regions of North America and China there are founnbsp;many thousand feet of strata above the typical Archaean rocksnbsp;and below the newer fossiliferous beds of Cambrian age. Itnbsp;IS reasonable to suppose that future research may extend thenbsp;present limits of fossil-bearing rocks below the horizon, whichnbsp;is marked by the occurrence of the widely distributed andnbsp;oldest known trilobite, the genus Olenellus.

The vast thickness of Cambrian strata was for the most part laid down on the floor of a comparatively deep sea; othernbsp;members of the series represent the shingle beaches and coastnbsp;deposits accumulated on the slopes of Archaean islands.nbsp;There have been many conjectures as to the distribution ofnbsp;land and sea during the deposition of these rocks; but thenbsp;data are too imperfect to enable us to restore with any degreenbsp;of confidence the physical geography of this Palaeozoic epoch,nbsp;of which the sediments stood out as islands of Cambrian landnbsp;during many succeeding ages.

III. Ordovician.

Since the days when Sedgwick and Murchison first worked out the succession of Palaeozoic strata in North Wales, therenbsp;has always existed a considerable difference of opinion as tonbsp;the best method of subdividing the Cambrian-Silunan strata.nbsp;Later research has shown that the rocks included by Sedgwicknbsp;in his Cambrian system, fall naturally into two groups; fornbsp;the upper of these Prof. Lapworth has suggested the termnbsp;Ordovician, from the name of the Ordovices, who inhabited anbsp;part of northern Wales. At the base of the system we have anbsp;series of volcanic and sedimentary rocks to which Sedgwick gavenbsp;the name Arenig; above these there occur the Llandeilo Flags,nbsp;succeeded by a considerable thickness of rocks known as thenbsp;Bala series. The rocks making up these Ordovician sedimentsnbsp;consist for the most part of slates, sandstones and limestones with

volcanic ashes and lavas. Much of the typical Welsh scenery owes its character to the folded and weathered rocks laid downnbsp;on the floor of the Ordovician sea, on which from many centresnbsp;of volcanic activity lava streams and showers of ash werenbsp;spread out between sheets of marine sediment. The Arenignbsp;Hills, Snowdonia, and many other parts of North and Southnbsp;Wales, parts of Shropshire, Scotland, Sweden, Russia, Bohemia,nbsp;North America and other regions consist of great thicknessesnbsp;of Ordovician strata.

Passing up a stage higher in the geologic series, we have a succession of conglomerates, sandstones, shales, andnbsp;limestones; in other words, a series of beds which representnbsp;pebbly shore deposits, the sands and muds of deeper water,nbsp;and the accumulated d�bris of calcareous skeletons of animals ^nbsp;which lived in the clear water of the Silurian sea. The termnbsp;Silurian (Siluria was the country of Caractacus and the oldnbsp;Britons known as Silures^) was first applied by Murchison innbsp;1835 to a more comprehensive series of rocks than are nownbsp;included in the Silurian system. The rocks of this period occurnbsp;in Wales, Shropshire, parts of Scotland, Ireland, Scandinavia,nbsp;Russia, the United States and other countries. After thenbsp;accumulation of the thick Ordovician sediments, the sea-floornbsp;was upraised and in places converted into ridges or islands ofnbsp;land, of which the detritus formed part of the material ofnbsp;Silurian deposits. The limestones of the Wenlock ridge havenbsp;yielded an abundant fauna, consisting of corals, crinoids,nbsp;molluscs and other invertebrates. In this period we havenbsp;the first representatives of the Vertebrata, discovered in thenbsp;rocks of Ludlow. In fact, in the Silurian period, �all thenbsp;great divisions of the Animal Kingdom were already repre-sented''^.�

V. Devonian.

By the continued elevation of the Silurian sea-floor, large portions tecaine dry land, and during the succeeding perionbsp;most of the British area formed part of a continental mass.nbsp;Over the southern part of England, there still lay an arm of thenbsp;sea, and in this were laid down the marine sediments whmhnbsp;now form part of Devon, and from which the name Devoniannbsp;has been taken as a convenient designation for the strata ofnbsp;this period In parts of the northern land, in the region nownbsp;occupied by Scotland, there were large inland lakes, on thenbsp;floor of which vast thicknesses of shingle beds and coarsenbsp;sands (�Old Red Sandstone�) were slowly accumulated-, andnbsp;it has been shown by Sir Archibald Geikie and others thatnbsp;during this epoch there were considerable outpourings ofnbsp;volcanic material in the Scotch area.

Farther to the West and South-west there was another large lake in which the so-called Kiltorkan beds of Irelandnbsp;^ore deposited. In these Irish sediments, and others of thenbsp;same age in Belgium and elsewhere a few forms of land plantsnbsp;flave been discovered; but it is from the Devonian rocks ofnbsp;I^orth America that most of our knowledge of the flora of thisnbsp;period has been obtained.

VI. Carboniferous.

From the point of view of palaeobotany, the shales, sandstones, and seams of coal included in the Carboniferous system are of special interest. It is from the relics of this Palaeozoic

The following classification of Carboniferous rocks shows the order of succession of the various beds, and the nature ofnbsp;the rocks which

In the classification of Carboniferous rocks adopted in Geikie's text-book of Geology the following arrangement isnbsp;followed for the Carboniferous limestone series^:�

Yoredale group of shales and grits passing down into dark shales and limestones.nbsp;Thick {Scaur or Main) limestone in thenbsp;south and centre of England and Ireland, passing northwards into sandstones, shales and coals with limestones.

centre of England. The Calciferous sandstone group of Scotland (marine,nbsp;estuarine, and terrestrial organisms)nbsp;probably represents the Scaur limestonenbsp;and lower limestone shale, and graduatesnbsp;downwards insensibly into the Uppernbsp;Old Red Sandstone.

The thick beds of mountain limestone, with their characteristic marine fossil shells and corals play an important part in English scenery. In Derbyshire, West Yorkshire, and othernbsp;places, the limestone crags and hills are made up of the raisednbsp;floor of a comparatively deep Carboniferous sea, which coverednbsp;a considerable portion of the British Isles at the beginning'nbsp;of this epoch.

The accumulation of the calcareous skeletons of marine animals, with masses of coral, veritable shell-banks of extinctnbsp;oyster-like lamellibranchs, built up during the lapse of a longnbsp;period of time, formed widespread deposits of calcareousnbsp;gt; Kidston (94).nbsp;nbsp;nbsp;nbsp;2 Qeikie (93), p. 825.

continued, and the sea was by some means more confined fresh-water or brackis area,nbsp;nbsp;nbsp;nbsp;, ^ derived

surface which supported a luxuriant vege a ion, debris was subsequently converted intnbsp;nbsp;nbsp;nbsp;^

ot tn. period, the Earth's surface in ��=*�quot;�, subjected to crust-foldings on a large scale �nbsp;nbsp;nbsp;nbsp;t*o

sets of movements resulting in the formation o g^^dstones boniferous rocks. The uppermost series g �nbsp;nbsp;nbsp;nbsp;.

and coal-seams were in great part removed J enn fo^gr-the crests of the elevated ridges, but remaine m vening troughs or basins where theynbsp;nbsp;nbsp;nbsp;have

onr Coal-Measures preserved in the form of detached upper Carboniferous beds.nbsp;nbsp;nbsp;nbsp;.nbsp;nbsp;nbsp;nbsp;and

A closer examination of the comparative thick succession of Carboniferous rocks in different � inbsp;shows very clearly that in the northern area onbsp;nbsp;nbsp;nbsp;^

iu the North of England the conditions were those which obtained further South. Seeing ow ^nbsp;botanical interest attaches to these rocks, it is imnbsp;treat a little more fully of their geology.nbsp;nbsp;nbsp;nbsp;tipvo-

rocks which have yielded a comparatively small number of Carboniferous fossils. To this succession of limestones, shalesnbsp;and grits the term Culm-Measu7'es was applied by Sedgwicknbsp;and Murchison in 1837. The rocks of this series occupy anbsp;trough between the Devonian rocks of North and Southnbsp;Devon. While some authorities have correlated the Culm-Measures with the Millstone Grit, others regard them as representing a portion of the true Coal-Measures, as well as thenbsp;Carboniferous and Lower Limestone Shaleh It has recentlynbsp;been shown that among the lower Culm strata there occurnbsp;bands of ancient deep-sea sediments, consisting of beds ofnbsp;chert containing siliceous casts of various species of Radiolaria.nbsp;There can be no doubt that the discovery of deep-sea fossilsnbsp;in this particular development of the British Carboniferousnbsp;system leads to the conclusion that � while the massivenbsp;deposits of the Carboniferous limestone�formed of the skeletons of calcareous organisms�were in process of growth innbsp;the seas to the North, there existed to the South-west anbsp;deeper ocean in which siliceous organisms predominated andnbsp;formed these siliceous radiolarian rocks'^.�

The Upper Culm-Measures consist of conglomerates, grits, sandstones and shales with some plant remains and othernbsp;fossils, and constitute a typical set of shallow water sediments.nbsp;In Westphalia, the Harz region, Thuringia, Silesia and Moravianbsp;there are rocks corresponding to the Culm-Measures of Devon,nbsp;and some of these have also afforded evidence of deep waternbsp;conditions.

S. W. England, 8. Wales, Derbyshire and Yorkshire. In these districts the Carboniferous limestone reaches a considerable thickness; in the Mendips it has a thickness ofnbsp;3000 feet, and in the Pennine chain of 4000 feet. At the basenbsp;of this limestone series there occurs in the southern districtsnbsp;the so-called lower limestone shale, consisting of clays, shalesnbsp;and sandy beds. Above the limestone we have the Millstonenbsp;grit and Coal-Measures; but in the Pennine district there isnbsp;a series of rocks consisting of impure limestones and shales.

has been proposed. In the Isle of Man and Derbysh of lava are irbedded with the calcareous sednnents.nbsp;clear proof of submarine volcanic eruptions.nbsp;nbsp;nbsp;nbsp;of

N. England mid Scotland. In the Garbo ^ g^^^yower Northumberland we have distinctnbsp;nbsp;nbsp;nbsp;in West

spoken of as the Caldferoiis sandstone, an , , j^av be Garhoniferous limestone. The calciferovis san s

compared with the lower limestone � ^ � ifpvons lime-Carboniferons limestone of England. The ar on stone of Scotland probably represents the upper pnbsp;limestone of EnglaU and the Yoredale rocks of the l^enn

Turning to the upper members of t e a system�in the Coal-Measures, as they were ca ,nbsp;by William Smith,�we have a series of coalnbsp;shales, and ironstones occurring for the mos pnbsp;shaped ��u AS u g�erul rule eachnbsp;nbsp;nbsp;nbsp;on

The usual classification adopted for the British Coal-Measures is that of Upper, Middle, and Lower Coal-Measures; between the Upper and Middle divisions there occur certainnbsp;transition or passage beds which are known as the Transitionnbsp;series. Continental writers, and more recently Mr Kidston ofnbsp;Stirling, have attempted with considerable success to correlatenbsp;the Coal-producing strata by means of fossil plantsh

Vertical section of the Bassey or Salts Coal seam. Rushton Colliery, Blackburn (Lower Coal-Measures). From a specimen 4 feet 4 inches in height,nbsp;presented by Mr P. W. Pickup to the Manchester Museum, Owens College.

Finally, some reference must be made to the occurrence of Carboniferous rocks underneath more recent strata. In anbsp;geological map, or bird�s-eye view of a country, we see suchnbsp;rocks as appear at the surface; by means of deep borings,nbsp;however, we are occasionally enabled to follow the course ofnbsp;older beds a considerable distance below the usually accessiblenbsp;^ Kidston (94).

part of the Earth�s crust. In the neighbourhood of London, Dover, and other places we have Tertiary and Mesozoic stratanbsp;forming the surface of the country, but below these comparative ynbsp;recent formations, the sinking of deep wells and other boringsnbsp;have proved the� existence of a ridge of Palaeozoic rocksnbsp;stretching from the South Wales Coal-field through the Southeast of England to northern France, Belgium and Westphalia.nbsp;It is from rocks forming part of this old ridge that characteristicnbsp;Goal-Measure plants have been obtained from the Dover boring.nbsp;In Pig. 5 ig shown an almost complete pinnule of Neuropterisnbsp;Scheiichzeri Hoffm., a well-known fern, marking a definite

pinnules, shown in the figure as fine lines lying m � parallel to the midrib and across the lateral veins,nbsp;characteristic feature of this species.

VII. Permian.

Beference has already been made to the earth-foldings which marked the close of Carboniferous times; �the opennbsp;Mediterranean sea of the Carboniferous period in Europe wasnbsp;converted into a large inland sea, like the Caspian of thenbsp;present day, surrounded by a rocky and hilly continent, onnbsp;which grew trees and plants of various kindsb� In parts of

^ Vide Zeiller (92) for a list of species of Coal-Measure plants found in, the pieces of shale included in the core brought up by the borer.

Lancashire, Westmoreland, the Eden Valley, and in the East of England from Sunderland to Nottingham, there occurs a succession of limestones, sandstones, clays and other rocks withnbsp;occasional beds of rock-salt and gypsum, which represent thenbsp;various forms of sediment and chemical precipitates formed onnbsp;the floor of Permian lakes. The poverty of the fauna andnbsp;flora of Permian strata points to conditions unfavourable tonbsp;life; and there can be little doubt that the characteristic rednbsp;rocks of St Bees Head, and the creamy limestones of thenbsp;Durham coast are the upraised sediments of an inland saltwater lake. The term Dyas was proposed by Marcou for thisnbsp;series of strata as represented in Germany, where the rocks arenbsp;conveniently grouped in two series, the Magnesian limestonenbsp;or Zechstein and the red sandstones or Rotheliegendes. Thenbsp;�older and better known name of Permian was instituted bynbsp;Murchison for the rocks of this age, from their extreme development in the old kingdom of Permia in Russia. Unfortunately considerable confusion has arisen from the emplo}^mentnbsp;of different names for rocks of the same geological period ; andnbsp;the grouping of the beds varies in different parts of the world.nbsp;It is of interest to note, that in the Tyrol, Carinthia, and othernbsp;places there are found patches of old marine beds which werenbsp;originally laid down in an open sea, which extended over thenbsp;site of the Mediterranean, into Russia and Asia. In Bohemia,nbsp;the Harz district, Autun in Burgundy, and other regions,nbsp;there are seams of Permian coal interstratified with the marlsnbsp;and sands. From these last named beds many fossil plantsnbsp;have been obtained, and important palaeobotanical facts broughtnbsp;to light by the investigations of continental workers. Volcanicnbsp;eruptions, accompanied by lava streams and showers of ash,nbsp;have been recognised in the Permian rocks of Scotland, andnbsp;elsewhere.

In North America, Australia, and India the term Permo-Carboniferous is often made use of in reference to the continuous and regular sequence of beds which were formed towards the close of the Carboniferous and into the succeeding Permiannbsp;epoch. The enormous series of freshwater Indian rocks, tonbsp;which geologists have given the name of the Gondwana

SYSTEM, includes the- sediments of more than one geological period, some of the older members being regarded as Permo-Carboniferous in age. These Indian beds, with others mnbsp;Australia, South Africa, and South America, are of specialnbsp;interest on account of the characteristic southern hemispherenbsp;plants which they have afforded, and from the association withnbsp;the fossiliferons strata of extensive boulder beds pointing tonbsp;idespread glacial conditions.

YIIl. Trias.

tions ofl marked change in the records o life. Many of the characteristic Palaeozoic ossi snbsp;represented, and in their place we meet wi ^ ^^^.ggtold

formation; the more restricted German Trias, on the other hand, is a shallow shore, bay or inland sea formation'.�

In the Keuper beds of southern Sweden there are found workable seams of coal, and the beds of this district havenbsp;yielded numerous well-preserved examples of the Triassic flora.nbsp;A more impure coal occurs in the lower Keuper of Thuringianbsp;and S.-W. Germany, and to this group of rocks the termnbsp;Lettenkohle is occasionally applied.

In the Rhaetic Alps of Lombardy, in the Tyrol, and in England, from Yorkshire to Lyme Regis, Devonshire, Somersetshire, and other districts there are certain strata at the topnbsp;of the Triassic system known as the Rhaetic or Penarth beds.nbsp;The uppermost Rhaetic beds, often described as the Whitenbsp;Lias, afford evidence of a change from the salt lakes of thenbsp;Trias to the open sea of the succeeding Jurassic period.nbsp;Passing beyond this period of salt lakes and wind-swept barrennbsp;tracts of land, we enter on another phase of the earth�s history.

The Jura mountains of western Switzerland consist in great part of folded and contorted rocks which were originallynbsp;deposited on the floor of a Jurassic sea. In England thenbsp;Jurassic rocks are of special interest, both for geological andnbsp;historical reasons, as it is in them that we find a rich fauna andnbsp;flora of Mesozoic age, and it was the classification of these bedsnbsp;by means of their fossil contents that gained for William Smithnbsp;the title of the Father of English Geology. A glance at anbsp;geological map of England shows a band of Jurassic rocksnbsp;stretching across from the Yorkshire coast to Dorset. These arenbsp;in a large measure calcareous, argillaceous, and arenaceousnbsp;sediments of an open sea; but towards the upper limit of thenbsp;series, both freshwater and terrestrial beds are met with. Numerous fragments of old coral reefs, sea-urchins, crinoids, andnbsp;other marine fossils are especially abundant; in the freshwaternbsp;beds and old surface-soils, as well as in the marine sandstones

and shales, we have remnants of an exceedingly rich and apparently tropical vegetation. This was an age of Reptiles as well disr\^^^ of Cycads. An interesting feature of these widely

considerably, in one area a series is ma nbsp;nbsp;nbsp;Pnbsp;nbsp;nbsp;nbsp;,^ve

Lias rook, hare been further subdir.ded into ��JV of the species of Ammonites which form sonbsp;nbsp;nbsp;nbsp;there

feature of the Jurassic fauna. In the lower �� Vo-mte and are shelly limestones, clays, sandstones, and e s o^ ^nbsp;ironstone. Without disLssing the other -^divisions oMh ^nbsp;Jurassic period, we may note that in the uppermo

In the south of England, and in some other districts, it is difficult to draw any definite line between the uppermost stratanbsp;of the Jurassic and the lowest of the Cretaceous period. Thenbsp;rocks of the so-called Wealden series of Kent, Sursey, Sussex,nbsp;and the Isle of Wight, are usually classed as Lower Cretaceous,nbsp;but there is strong evidence in favour of regarding them asnbsp;sediments of the Jurassic period. The Cretaceous rocks ofnbsp;England are generally speaking parallel to the Jurassic strata,nbsp;and occupy a stretch of country from the east of Yorkshirenbsp;and the Norfolk coast to Dorset in the south-west. The Chalknbsp;downs and clififs represent the most familiar type of Cretaceousnbsp;strata. In the white chalk with its numerous flints, we havenbsp;part of the elevated floor of a comparatively deep sea, whichnbsp;extended in Cretaceous times over a large portion of the eastnbsp;and south-east of England and other portions of the Europeannbsp;continent. On the bed of this sea, beyond the reach of anynbsp;river-borne detritus, there accumulated through long ages thenbsp;calcareous and siliceous remains of marine animals, to henbsp;afterwards converted into chalk and flints. At the beginningnbsp;of the period, however, other conditions obtained, and therenbsp;extended over the south-east of England, and parts of northnbsp;and north-west Germany and Belgium, a lake or estuary innbsp;which were built up deposits of clay, sand and other material,nbsp;forming the delta of one or more large rivers. For thesenbsp;sediments the name Wealden was suggested in 1828. Eventually the gradual subsidence of this area led to an incursion ofnbsp;the sea, and the delta became overflowed by the waters of anbsp;large Cretaceous sea. At first the sea was shallow, and in itnbsp;were laid down coarse sands and other sediments known as thenbsp;Loiuer Greensand rocks. By degrees, as the subsidence continued,nbsp;the shallows became deep water, and calcareous material slowlynbsp;accumulated, to be at last upraised as beds of white chalk. Thenbsp;distribution of fossils in the Cretaceous rocks of north andnbsp;south Europe distinctly points to the existence of two fairlynbsp;well-marked sets of organisms in the two regions; no doubt the

expression of climatal zones similar to those recognised in Jurassic times. In North America, Cretaceous rocks are spread over a wide area, also in North Africa, India, South Africa, and othernbsp;parts of the world. Within the Arctic Circle strata of this agenbsp;ave become famous, chiefly on account of the rich flora de-^rom them by the Swiss palaeobotanist Heer. The faunanbsp;�a flora of this epoch are alike in their advanced state ofnbsp;6 opment and in the great variety of specific types; thenbsp;rg est class of plants is first met with at the base of thenbsp;'-cretaceous system.

distribution of land and water, and also in the development organic life, so great and universal, that it has scarcely beennbsp;^^^afied at any other period of the earth�s geological^history!�

e ertiary period seems to bring us suddenly to the threshold ar^'^^ times. In England at least, the deposits of this agenbsp;tain� nature of loose sands, clays and other materials contonbsp;nbsp;nbsp;nbsp;bones, and fossil plants bearing a close resemblance

present era. The chalk rocks, upheaved from Britai^*^^^*^^�'^^nbsp;nbsp;nbsp;nbsp;land over a large part of

their material was in time removed by the ^cne tfinbsp;nbsp;nbsp;nbsp;agents, and the rest gradually sank again

south f quot;�^'fers of Tertiary lakes and est\iaries. In the rocks hnbsp;nbsp;nbsp;nbsp;^nd in north Europe generally, the Tertiary

southe �nffered but little disturbance or folding, but in sands h^ nrope and other parts of the world, the Tertiar}'nbsp;involved'quot;'^ compacted and hardened into sandstones, andnbsp;many ofnbsp;nbsp;nbsp;nbsp;gigantic crust-movements which gave birth to

of piled'^^*' Himalayas, and other ranges consist to a large extent The V 1nbsp;nbsp;nbsp;nbsp;strangely folded layers of old Tertiary sediments,

narta ^ Giants Causeway, the Isle of Staffa, and other parts of western Sclt;,tland.

4�2

During the succeeding phases of this period, the distribution of land and sea was continually changing, climatic conditions varied within wide limits; and in short wherevernbsp;Tertiary fossiliferous beds occur, we find distinct evidence of annbsp;age characterised by striking activity both as regards thenbsp;action of dynamical as well as of organic forces. Sir Charlesnbsp;Lyell proposed a subdivision of the strata of this period intonbsp;Eocene, Miocene, and Pliocene, founding his classification onnbsp;the percentage of recent species of molluscs contained in thenbsp;various sets of rocks. His divisions have been generally adopted.nbsp;In 1854 Prof Beyrich proposed to include another subdivision in the Tertiary system, and to this he gave the namenbsp;Oligocene.'

Occupying a basin-shaped area around London and Paris there are beds of Eocene sands and clays which were originallynbsp;deposited as continuous sheets of sediment in water at firstnbsp;salt, afterwards brackish and to a certain extent fresh. In thenbsp;Hampshire cliffs and in some parts of the Isle of Wight, we havenbsp;other patches of these oldest Tertiary sediments. Across thenbsp;south of Europe, North Africa, Arabia, Persia, the Himalayas, tonbsp;Java and the Philippine islands, there existed in early Tertiarynbsp;times a wide sea connecting the Atlantic and Pacific oceans;nbsp;and it may be that in the Mediterranean of to-day we have anbsp;remnant of this large Eocene ocean. Later in the Tertiarynbsp;period a similar series of beds was deposited which we nownbsp;refer to as the Oligocene strata; such occurs in the cliffs ofnbsp;Headon hill in the Isle of Wight, containing bones of crocodiles, and turtles, with the relics of a rich flora preserved innbsp;the delta deposits of an Oligocene river. At a still later stagenbsp;the British area was pi�obably dry land, and an open sea existednbsp;over the Mediterranean region. In the neighbourhood ofnbsp;Vienna we have beds of this age represented by a succession ofnbsp;sediments, at first marine and afterwards freshwater. Miocenenbsp;beds occur over a considerable area in Switzerland and thenbsp;Arctic regions, and they have yielded a rich harvest to palaeo-botanical investigators.

On the coast of Essex, Suffolk, Norfolk, the south of Cornwall, and other districts there occur beds of shelly sand

and gravel long known under the name of � Crag.� The beds have a very modern aspect; the sands have not been convertednbsp;lato sandstones, and the shells have undergone but little change.nbsp;These materials were for the most part accumulated on thenbsp;hed of a shallow sea which swept over a portion of East Anglianbsp;la Pliocene times. In the sediments of this age northern formsnbsp;of shells and other organisms make their appearance, and innbsp;the Cromer forest-bed there occur portions of drifted trees withnbsp;�3-nds, clays and gravels, representing in all probability thenbsp;if^bris thrown down on the banks of an ancient river. At thisnbsp;time the greater part of the North Sea was probably a low-^ying forest-covered region, through which flowed the waters ofnbsp;a large river, of which part still exists in the modern Rhine.

ae lowering of temperature which became distinctly pro-aounced in the Pliocene age, continued until the greater part af Britain and north Europe experienced a glacial period, andnbsp;�ach conditions obtained as we find to-day in icp-coverednbsp;Greenland. Finally the ice-sheet melted, the local glaciers ofnbsp;orth Wales, the English Lake district and other hilly regions,nbsp;1�etreated, and after repeated alterations in level, the land ofnbsp;Great Britain assumed its modern form. The submergednbsp;forests and peat beds familiar in many parts of the coast, thenbsp;diatomaceous deposits of dried up lakes, �remain as the verynbsp;finger touches of the last geological change.�

The agents of change and geological evolution, which we passed in brief review, are still constantly at work carryingnbsp;one step further the history of the earth. A superficial reviewnbsp;�f geological history gives us an impression of recurring andnbsp;'quot;'ide-spread convulsions, and rapidly effected revolutions innbsp;organic life and geographical conditions ; on the other hand anbsp;closer comparison of the past and present, with due allowancenbsp;for the enormous period of time represented by the recordsnbsp;of the rocks, helps us to realise the continuity of geologicalnbsp;evolution. � So that within the whole of the immense periodnbsp;indicated by the fossiliferous stratified rocks, there is assuredlynbsp;^t the slightest proof of any break in the uniformity ofnbsp;ature s operations, no indication that events have followednbsp;other than a clear and orderly sequence^�

CHAPTER IV.

The discovery of a fossil, whether as an impression on the surface of a slab of rock or as a piece of petrified wood,nbsp;naturally leads us hack to the living plant, and invites speculation as to the circumstances which led to the preservationnbsp;of the plant fragment. There is a certain fascination innbsp;endeavouring, with more or less success, to picture the exactnbsp;conditions which obtained when the leaf or stem was carriednbsp;along by running water and finally sealed up in a sedimentarynbsp;matrix. Attempts to answer the question�How came thenbsp;plant remains to be preserved as fossils ?�are not merely ofnbsp;abstract interest appealing to the imagination, but are ofnbsp;considerable importance in the correct interpretation of thenbsp;facts which are to he gleaned from the records of plant-bearingnbsp;strata.

Before describing any specific examples of the commoner methods of fossilisation; we shall do well to briefly considernbsp;how plants are now supplying material for the fossils of anbsp;future age. In the great majority of cases, an appreciationnbsp;of the conditions of sedimentation, and of the varied circumstances attending the transport and accumulation of vegetablenbsp;d�bris, supplies the solution of a problem akin to that of thenbsp;fly in amber and the manner in which it came there.

Seeing that the greater part of the sedhnentary strata have been formed in the sea, and as the sea rather than the land hasnbsp;been for the most part the scene of rock-building in the past, itnbsp;is not surprising that fossil plants are far less numerous thannbsp;fossil animals. With the exception of the algae and a fewnbsp;representatives of other classes of plants, which live in thenbsp;snallow-water belt round the coast, or in inland lakes and seas,nbsp;plants are confined to land-surfaces; and unless theii remainsnbsp;are swept along by streams and embedded in sediments whichnbsp;are accumulating on the sea floor, the chance of their preservation is but small. The strata richest in fossil plants are oftennbsp;those which have been laid down on the floor of an inland lakenbsp;spread out as river-borne sediment under the waters of annbsp;sstuary. Unlike the hard endo- and exo-skeletons of animals,nbsp;the majority of plants are composed of comparatively softnbsp;material, and are less likely to be preserved or to retain theirnbsp;�^I'iginal form when exposed to the wear and tear which mustnbsp;�^ften accompany the process of fossilisation.

The Coal-Measure rocks have furnished numberless relics a Palaeozoic vegetation, and these occur in various forms ofnbsp;preservation in rocks laid down in shallow water on the edgenbsp;of a forest-covered land. The underclays or unstratifiednbsp;argillaceous beds which nearly always underlie each seam ofnbsp;coal have often been described as old surface-soils, containingnbsp;numerous remains of roots and creeping underground stems ofnbsp;forest trees. The overlying coal has been regarded as a massnbsp;uf the carbonised and compressed debris of luxuriant forestsnbsp;which grew on the actual spot now occupied by the beds of coal.nbsp;There are, however, many arguments in favour of regarding thenbsp;Coal seams as beds of altered vegetable material which wasnbsp;spread out on the floor of a lagoon or lake, while the underclaynbsp;Was an old soil covered by shallow water or possibly a swampynbsp;Surface tenanted by marsh-loving plants'.

The Jurassic beds of the Yorkshire Coast, long famous as some of the richest plant-bearing strata in Britain, and thenbsp;Wealden rocks of the south coast afford examples of Mesozoicnbsp;sediments which were laid down on the floor of an estuary ornbsp;^ Discussed at greater length in vol. ii.

large lake. Circumstances have occasionally rendered possible the preservation of old land-surfaces with the stumps of treesnbsp;still in their position of growth. One of the best examples ofnbsp;this in Britain are the so-called dirt-beds or black bands ofnbsp;Portland and the Dorset Coast. On the cliffs immediately eastnbsp;of Lulworth Cove, the surface of a ledge of Purheck limestonenbsp;which juts out near the top of the cliffs, is seen to have thenbsp;form here and there of rounded projecting bosses or � Suits �nbsp;several feet in diameter. In the centre of each boss there isnbsp;either an empty depression, or the remnants of a silicified stemnbsp;of a coniferous tree. Blocks of limestone 3 to 5 feet long andnbsp;of about equal thickness may be found lying on the rockynbsp;ledge presenting the appearance of massive sarcophagi innbsp;which the central trough still contains the silicified remainsnbsp;of an entombed tree. The calcareous sediment no doubtnbsp;oozed up to envelope the thick stem as it sank into the softnbsp;mud. An examination of the rock just below the bed bearingnbsp;these curious circular elevations reveals the existence of anbsp;comparatively narrow band of softer material, which has beennbsp;worn away by denuding agents more rapidly than the over-lying limestone. This band consists of partially rounded ornbsp;subangular stones associated with carbonaceous material, andnbsp;probably marks the site of an old surface-soil. This old soil isnbsp;well shown in the cliffs and quarries of Portland, and similarnbsp;dirt-beds occur at various horizons in the Lower and Middlenbsp;Purbeck Seriesh In this case, then, we have intercalated in anbsp;series of limestone beds containing marine and freshwaternbsp;shells two or three plant beds containing numerous and frequently large specimens of cycadean and coniferous stems,nbsp;lying horizontally or standing in their original position ofnbsp;growth. These are vestiges of an ancient forest which spreadnbsp;over a considerable extent of country towards the close of thenbsp;Jurassic period. The trunks of cycads, long familiar in thenbsp;Isle of Portland as fossil crows� nests, have usually the form ofnbsp;round depressed stems with the central portion somewhat hollowed out. It was supposed by the quarrymen that they werenbsp;petrified birds� nests which had been built in the forks of thenbsp;1 Woodward, H. B. (95), Figs. 124 and 133 from photographs by Mr Strahan.

trees which grew in the Portland forest. The beds separating the surface-soils of the Purbeck Series, as seen in the sectionsnbsp;exposed on the cliffs or quarries, point to the subsidence of anbsp;forest-covered area over which beds of water-borne sedimentnbsp;were gradually deposited, until in time the area became drynbsp;land and was again taken possession of by a subtropical vegetation, to be once more depressed and sealed up under layers ofnbsp;sedimentb

A still more striking example of the preservation of forest trees rooted in an old surface-soil is afforded by the so-callednbsp;fossil-grove in Victoria Park, Glasgow, (Frontispiece). Thenbsp;stumps of several trees, varying in diameter from about one tonbsp;three feet, are fixed by long forking � roots � in a bed of shale.nbsp;In some cases the spreading �roots,� which bear the surfacenbsp;features of Stigmaria, extend for a distance of more than tennbsp;feet from the base of the trunk. The stem surface is markednbsp;by irregular wrinklings which suggest a fissured bark; but thenbsp;superficial characters are very imperfectly preserved. In onenbsp;place a flattened Lepidodendron stem, about 30 feet long, liesrnbsp;prone on the shale. Each of the rooted stumps is oval ornbsp;elliptical in section, and the long axes of the several stems arenbsp;approximately parallel, pointing to some cause operating in anbsp;definite direction which gave to the stems their present form.nbsp;Near one of the trees, and at a somewhat higher level than itsnbsp;base, the surface of the rock is clearly ripple-marked, and takesnbsp;us back to the time w'hen the sinking forest trees were washednbsp;by Avaves which left an impress in the soft mud laid down overnbsp;the submerged area. The stumps appear to be those of Lepidodendron trees, rooted in Lower Carboniferous rocks. Fromnbsp;their manner of occurrence it would seem that we have innbsp;them a corner of a Palaeozoic forest in which Lepidodendranbsp;played a conspicuous part. The shales and sandstones containing the fossil trees were originally overlain by a bed ofnbsp;igneous rock which had been forced up as a sheet of lava intonbsp;the hardened sands and clays-.

Other examples of old surface-soils occur in different parts of the world and in rocks of various ages. As an instance of a

land surface preserved in a different manner, reference may be made to the thin bands of reddish or brown material as wellnbsp;as clays and shale which occasionally occur between the sheetsnbsp;of T.ertiary lava in the Western Isles of Scotland and thenbsp;north-east of Ireland. In the intervals between successivenbsp;outpourings of basaltic lava in the north-west of Europe duringnbsp;the early part of the Tertiary period, the heated rocks becamenbsp;gradually cooler, and under the influence of weathering agentsnbsp;a surface-soil was produced fit for the growth of plants. Innbsp;some places, too, shallow lakes were formed, and leaves, fruitsnbsp;and twigs became embedded in lacustrine sediments, to benbsp;afterwards sealed up by later streams of lava. In the face ofnbsp;the cliff at Ardtun Head on the coast of Mull a leaf-bed isnbsp;exposed between two masses of gravel underlying a basalticnbsp;lava flow; the impressions of the leaves of Gingko and othernbsp;plants from the Tertiary sediments of this district are exceptionally beautiful and well preserved! A large collectionnbsp;obtained by Mr Starkie Gardner may be seen in the Britishnbsp;Museum.

In 1883 the Malayan island of Krakatoa, 20 miles from Sumatra and Java, was the scene of an exceptionally violentnbsp;volcanic explosion. Two-thirds of the island were blown away,nbsp;and the remnant was left absolutelj^ bare of organic life. Innbsp;1886 it was found that several plants had already establishednbsp;themselves on the hardened and weathered crust of the Kraka-toan rocks, the surface of the lavas having been to a largenbsp;extent prepared for the growth of the higher plants by thenbsp;action of certain blue-green algae which represent some of thenbsp;lowest types of plant life! We may perhaps assume a somewhat similar state of things to have existed in the volcanicnbsp;area in north-west Europe, where the intervals between successive outpourings of lava are represented by the thin bands ofnbsp;leaf-beds and old surface-soils.

On tlie Cheshire Coast at Leasowe^ and other localities, there is exposed at low water a tract of black peaty groundnbsp;studded with old rooted stumps of conifers and other trees

(fig. 6). There is little reason to doubt that at all events the majority of the trees are in their natural place of growth. Thenbsp;peaty soil on which they rest contains numerous flattened stemsnbsp;of reeds and other plants, and is penetrated by roots, probablynbsp;of some aquatic or marshy plants which spread over the site ofnbsp;the forest as it became gradually submerged. A lower forest-bed rests directly on a foundation of boulder clay. Such submerged forests are by no means uncommon around the Britishnbsp;coast; many of them belong to a comparatively recent period,nbsp;posterior to the glacial age. In many cases, however, the treenbsp;stumps have been drifted from the places where they grew andnbsp;eventually deposited in their natural position, the roots of thenbsp;trees, in some cases aided by stones entangled in their branches,nbsp;being heavier than the stem portion. There is a promisingnbsp;field for botanical investigation in the careful analysis of thenbsp;floras of submerged forests; the work of Clement Keid,nbsp;Nathorst, Andersson and others, serves to illustrate the valuenbsp;of such research in the hands of competent students.

The following description by Lyell, taken from his American travels, is of interest as affording an example of the preservation of a surface-soil:

� On our way home from Charle.ston, by the railway from Orangeburg, I observed a thin black line of charred vegetable matter exposed in thenbsp;perpendicular section of the bank. The sand cast out in digging thenbsp;railway had been thrown up on the original soil, on which the pine forestnbsp;grew ; and farther excavations had laid open the junction of the rubbishnbsp;and the soil. As geologists, we may learn from this fact how a thin seamnbsp;of vegetable matter, an inch or two thick, is often the only monumentnbsp;to be looked for of an ancient surface of dry land, on which a luxuriantnbsp;forest may have grown for thousands of years. Even this seam of friablenbsp;matter may be washed away when the region is submerged, and, if not,nbsp;rain water percolating freely through the sand may, in the course of ages,nbsp;gradually carry away the carboid.�

In addition to the remnants of ancient soils, and the preservation of plant fragments in rocks which have been formed on the floor of an inland lake or an estuary, it is by no means rarenbsp;to find fossil plants in obviously marine sediments. In fig. 7 we

have a piece of coniferous wood with the shell of an Ammonite {Aegoceras planicosta Sow.) lying on it; the specimen was foundnbsp;in the Lower Lias clay at Lyme Regis, and illustrates thenbsp;accidental association of a drifted piece of a forest tree with a

Fig. 7. Aegoceras planicosta Sow. on a piece of coniferous wood, Lower Lias, Lyme Regis. From a specimen in the British Museum. Slightly reduced.

shell which marks at once the age and the marine character of the beds. Again in fig. 8 we have a block of flint partially enclosing a piece of coniferous wood in which the internal structurenbsp;has been clearly preserved in silica. This specimen was foundnbsp;in the chalk, a deposit laid down in the clear and deep waternbsp;of the Cretaceous sea. The wood must have floated for somenbsp;time before it became water-logged and sank to the sea-floor.nbsp;In the light coloured wood there occur here and there darknbsp;spots which mark the position of siliceous plugs h, h filling upnbsp;clean cut holes bored by Teredos in the woody tissue. The woodnbsp;became at last enclosed by siliceous sediment and its tissuesnbsp;penetrated by silica in solution, which gradually replaced andnbsp;preserved in wonderful perfection the form of the original

tissue. A similar instance of wood enclosed in flint was figured by Mantell in 1844 in his Medals of Creation'^.

The specimen represented in fig. 9 illustrates the almost complete destruction of a piece of wood by some boring animal.nbsp;The circular and oval dotted patches represent the filled upnbsp;cavities made by a Teredo or some similar wood-boring animal.

Before discussing a few more examples of fossils illustrating different methcjds of fossilisation, it way not he out of place tonbsp;quote a few extracts from travellers� narratives which enable usnbsp;to realise more readily the circumstances and conditions undernbsp;which plant remains have been preserved in the Earth�s crust.

In an account of a journey down the Rawas river in Sumatra, Forbes thus describes the flooded country:�

� The whole surface of the water �was covered, absolutely in a close sheet, with jjetals, fruits and leaves, of innumerable species. In placidnbsp;corners sometimes I noted a collected mass nearly half a foot deep, amongnbsp;which, on examination, I could scarcely find a leaf that was perfect, ornbsp;that remained attached to its rightful neighbour, so that were they tonbsp;become imbedded in some soft muddy spot, and in after ages to reappearnbsp;in a fossil form they would afford a few difficult puzzles to the palaeontologist, both to separate and to put together i.�

An interesting example of the mixture of plants and animals in sedimentary deposits is descidbed by Hooker in his Himalayan Journals:�

� To the geologist the Jheels and Sunderbunds are a most instructive region, as w'hatever may be the mean elevation of their waters, anbsp;permanent depression of ten to fifteen feet would submerge an immensenbsp;tract, which the Ganges, Burrampooter, and Soormah would soon covernbsp;with beds of silt and sand.

�There would be extremely few shells in the beds thus formed, the southern and northern divisions of w'hich w'ould present two very differentnbsp;floras and faunas, and �would in all probability be referred by futurenbsp;geologists to widely different epochs. To the north, beds of peat wouldnbsp;be formed by grasses, and in other parts temperate and tropical forms ofnbsp;plants and animals would be preserved in such equally balanced proportions as to confound the palaeontologist ; with the bones of thenbsp;long-snouted alligator, Gangetic porpoise, Indian cow, buffalo, rhinoceros,nbsp;elephant, tiger, deer, bear, and a host of other animals, he would meetnbsp;with acorns of several species of oak, pine-cones and magnolia fruits, rosenbsp;seeds, and Cycas nuts, with palm nuts, screw-pines, and other tropicalnbsp;productions^.�

Thunb., a low stemless palm that grows in the tidal waters of the Indian Ocean, and bears a large head of nuts. It is a plant of no interest to thenbsp;common observer, but of much to the geologist, from the nuts of a similarnbsp;plant abounding in the Tertiary formations at the mouth of the Thames,nbsp;having floated about there in as great profusion as here, till buried deepnbsp;in the silt and mud that now forms the island of SheppeyL�

Of the drifting of timber, fruits, amp;c., we find numerous accounts in the writings of travellers. Rod way thus describesnbsp;the formation of vegetable rafts in the rivers of Northern Britishnbsp;Guiana:�

�Sometimes a great tree, whose timber is light enough to float, gets entangled in the grass, and becomes the nucleus of an immense raft,nbsp;which is continually increasing in size as it gathers up everything thatnbsp;comes floating down the river�.�

The undermining of river banks in times of flood, and the transport of the drifted trees to be eventually deposited in thenbsp;delta is a familiar occurrence in many parts of the world. Thenbsp;more striking instances of such wholesale carrying along of treesnbsp;are supplied by Bates, Lyell and other writers. In his description of the Amazon the former writes :

� The currents ran with great force close to the bank, especially when these receded to form long bays or etiseadas, as they are called, and thennbsp;we made very little headway. In such places the banks consist of loosenbsp;earth, a rich crumbling vegetable movdd, supporting a growth of mostnbsp;luxuriant forest, of which the currents almost daily carry away largenbsp;portions, so that the stream for several yards out is encumbered withnbsp;fallen trees, whose branches quiver in the current^.�

� The rainy season had now set in over the region through which the great river flows ; the sand-banks and all the lower lands were alreadynbsp;under water, and the tearing current, two or three miles in breadth, borenbsp;along a continuous line of uprooted trees and islets of floating plants*.�

The rafts of the Mississippi and other rivers described by Lyell afford instructive examples of the distant transport of

* nbsp;nbsp;nbsp;Hooker, J. D. (91), p. 1. There are several good specimens of the blacknbsp;pyritised nipadite fruits in the British Museum and other collections.

vegetable material. The following passage is taken from the Principles of Geology,

� Within the tropics there are no ice-floes ; but, as if to compensate for that mode of transportation, there are floating islets of matted trees,nbsp;which are often borne along through considerable spaces. These arenbsp;sometimes seen sailing at the distance of fifty or one hundred miles fromnbsp;the mouth of the Ganges, with living trees standing erect upon them.nbsp;The Amazons, the Orinoco, and the Congo also produce these verdantnbsp;rafts I.�

After describing the enormous natural rafts of the Atchafa-laya, an arm of the Mississippi, and of the Ked river, Lyell goes on to say:

�The prodigious quantity of wood annually drifted down by the Mississippi and its tributaries is a subject of geological interest, notnbsp;merely as illustrating the manner in which abundance of vegetable matternbsp;becomes, in the ordinary course of nature, imbedded in submarine andnbsp;estuary deposits, but as attesting the constant destruction of soil andnbsp;transportation of matter to lower levels by the tendency of rivers to shift

the depth of several yards below the level of the sea, that the soil of the delta contains innumerable trunks of trees, layer above layer, somenbsp;prostrate as if drifted, others broken off near the bottom, but remainingnbsp;still erect, and with their roots spreading on all sides, as if in theirnbsp;natural position 2.�

The drifting of trees in the ocean is recorded by Darwin in his description of Keeling Island, and their action as vehiclesnbsp;for the transport of boulders is illustrated by the same account.

�In the channels of Tierra del Fuego large quantities of drift timber are cast upon the beach, yet it is extremely rare to meet a tree swimmingnbsp;in the water. These facts may possibly throw light on single stones,nbsp;whether angular or rounded, occasionally found embedded in fine sedimentary masses-'*.�

Fruits may often be carried long distances from land, and presei'ved in beds far from their original source. Whilstnbsp;cruising amongst the Solomon Islands, the Challenger metnbsp;with fruits of Barringtonia speciosa amp;c., 130�150 miles fromnbsp;the coast. Off the coast of New Guinea long lines of drift

wood were seen at right angles to the direction of the river; uprooted trees, logs, branches, and bark, often floating separately.

�The midribs of the leaves of a pinnate-leaved palm were abundant, and also the stems of a large cane grass {Sacckarum), like that sonbsp;abundant on the shores of the great river in Fiji. Various fruits of treesnbsp;and other fragments were abundant, usually floating confined in the midstnbsp;of the small aggregations into which the floating timber was everywhere

of which some of the pinnae were still present. The leaves evidently drop first to the bottom, whilst vegetable drift is floating from a shore ;nbsp;thus, as the debris sinks in the sea water, a deposit abounding innbsp;leaves, but with few fruits and little or no wood, will be formed nearnbsp;shore, whilst the wood and fruits will sink to the bottom farther off thenbsp;land. Much of the wood was floating suspended vertically in the water,nbsp;and most curiously, logs and short branch pieces thus floating oftennbsp;occurred in separate groups apart from the horizontally floating timber.nbsp;The sunken ends of the wood were not weighted by any attached massesnbsp;of soil or other load of any kind ; possibly the water penetrates certainnbsp;kinds of wood more easily in one direction with regard to its growth thannbsp;the other, hence one end becomes water-logged before the other� Thenbsp;wood which had been longest in the water was bored by a Pholas^.�

The bearing of this account on the manner of preservation of fossils, and the differential sorting so frequently seen in plantnbsp;beds, is sufficiently obvious.

As another instance of the great distance to which land plants may be carried out to sea and finall}^ buried in marinenbsp;strata, an observation by Bates may be cited. When 400 milesnbsp;from the mouth of the main Amazons, he writes :

�We passed numerous patches of floating grass mingled with tree trunks and withered foliage. Amongst these masses I espied many fruitsnbsp;of that peculiar Amazonian tree the Ubussu Palm ; this was the last Inbsp;saw of the great river^.�

The following additional extract from the narrative of the Cruise of H.M.S. Challenger illustrates in a striking degree thenbsp;conflicting evidence which the contents of fossiliferous bedsnbsp;may occasionally afford; it describes what was observed in annbsp;excursion from Sydney to Browera Creek, a branch of the mainnbsp;estuary or inlet into which flows the Hawkesbury river. It

was impossible to say where the river came to an end and the sea began. The Creek is described as a long tortuous arm ofnbsp;the sea, 10 to 15 miles long, with the side walls covered withnbsp;orchids and Platycerium. The ferns and palms were abundantnbsp;in the lateral shady glens; marine and inland animals lived innbsp;close proximity.

�Here is a narrow strip of the sea water, twenty miles distant from the open sea ; on a sandy shallow flat close to its head are to be seennbsp;basking in the sun numbers of sting-rays.... All over these flats, andnbsp;throughout the whole stretch of the creek, shoals of Grey Mullet are to benbsp;met with ; numerous other mr*rine fish inhabit the creek. Porpoisesnbsp;chase the mullet right up to the commencement of the sand-flat. At thenbsp;shores of the creek the rooks are covered with masses of excellent oystersnbsp;and mussel, and other shell-bearing molluscs are abundant, whilst a smallnbsp;crab is to be found in numbers in every crevice. On the other hand thenbsp;water is overhung by numerous species of forest trees, by orchids andnbsp;ferns, and other vegetation of all kinds ; mangroves grow only in thenbsp;shallow bays. The gum trees lean over the water in which swim thenbsp;Trygon and mullet, just as willows hang over a pool of carp. The sandynbsp;bottom is full of branches and stems of trees, and is covered in patchesnbsp;here and there by their leaves. Insects constantly fall in the water, andnbsp;are devoured by the mullet. Land birds of all kinds fly to and fro acrossnbsp;the creek, and when wounded may easily be drowned in it. Wallabiesnbsp;swim across occasionally, and may add their bones to the debris at thenbsp;bottom. Hence here is being formed a sandy deposit, in which may benbsp;found cetacean, marsupial, bird, fish, and insect remains, together withnbsp;land and sea shells, and fragments of a vast land flora ; yet how restrictednbsp;is the area occupied by this deposit, and how easily might survivingnbsp;fragments of such a record be missed by future geological explorers !i�

The term � fossil � suggests to the lay mind a petrifaction or a replacement by mineral matter of the plant tissues. In thenbsp;scientific sense, a fossil plant, that is a plant or part of a plantnbsp;whether in the form of a true petrifaction or a structurelessnbsp;mould or cast, which has been buried in the earth by naturalnbsp;causes, may be indistinguishable from a piece of recent woodnbsp;lately fallen from the parent tree. In the geologically recentnbsp;peat beds such little altered fossils (or sub-fossils) are commonnbsp;enough, and even in older rocks the more resistant parts of plantnbsp;fragments are often found in a practically unaltered state. Innbsp;the leaf impressions on an impervious clay, the brown-wallednbsp;1 Challenger (85), Narrative, vol. i. p. 459.

epidermis shows scarcely any indication of alteration since it was deposited in the soft mud of a river�s delta. Such fossilnbsp;leaves are common in the English Tertiary beds, and even innbsp;Palaeozoic rocks it is not uncommon to find an impression of anbsp;plant on a bed of shale from which the thin brown epidermisnbsp;may be peeled off the rock, and if microscopically examined itnbsp;will be found to have retained intact the contours of thenbsp;cuticularised epidermal cells. A striking example of a similarnbsp;method of preservation is afforded by the so-called paper-coalnbsp;of Culm age from the Province of Toula in Russiaf In thenbsp;Russian area the Carboniferous or Permian rocks have beennbsp;subjected to little lateral pressure, and unlike the beds of thenbsp;same age in Western Europe, they have not been folded and compressed by widespread and extensive crust-foldings. Instead ofnbsp;the hard seams of coal there occur beds of a dark brownnbsp;laminated material, made up very largely of the cuticles ofnbsp;Lepidodendroid plants.

From such examples we may natuially pass to fossils in which the plant structure has been converted into carbonaceous matter or even pure coal. Tbis form of preservation isnbsp;especially common in plant-bearing beds at various geologicalnbsp;horizons. In other cases, again, some mineral solution, oxide ofnbsp;iron, talc, and other substances, has replaced the plant tissues.nbsp;From the Coal-Measures of Switzerland Heer has figured nume--rous specimens of fern fronds and other plants in which the leafnbsp;form has been left on the dark coloured rock surface as a thinnbsp;layer of white talcose materiaP. In the Buntersandstone ofnbsp;the Vosges and other districts the red imperfectly preservednbsp;impressions of plant stems and leaves are familiar fossils^;nbsp;the carbonaceous substance of the tissues has been replaced bynbsp;a brown or red oxide of iron.

Plants frequently occur in the form of incrustations; and in fact incrustations, which may assume a variety of forms, arenbsp;the commonest kind of fossil. The action of incrusting springs,nbsp;or as they are often termed petrifying springs, is illustrated atnbsp;Knaresborough, in Yorkshire, and many other places where

water highly charged with carbonate of lime readily deposits calcium carbonate on objects placed in the path of the stream.

The travertine deposited in this manner forms an incrustation on plant fragments, and if the vegetable substance is subsequently removed by the action of water or decay, a mouldnbsp;of the embedded fragment is left in the calcareous matrix. Annbsp;instructive example of this form of preservation was describednbsp;in 1868 � by Sharpe from an old gravel pit near Northampton.nbsp;He found in a section eight feet high (fig. 10), a mass of incrustednbsp;plants of Ohara (a) resting on and overlain by a calcareous pastenbsp;(c) and (d) made up of the decomposed material of the overlyingnbsp;rock, and this again resting on sand. The place where the sectionnbsp;occurred was originally the site of a pool in which Stoneworts

grew in abundance. Large blocks of these incrusted Charas may be seen in the fo.ssil-plant gallery of the British Museum.

In the Natural History Museum in the Jardin des Plantes, Paris, one of the table-cases contains what appear to be smallnbsp;models of flowers in green wax. These are in reality castsnbsp;in wax of the moulds or cavities left in a mass of calcareousnbsp;travertine, on the decay and disappearance of the encrustednbsp;flowers and other plant fragments^. This porous calcareous

^ There are still more perfect casts from S�zanue in Prof. Munier-Chalmas� Geological collection in the Sorbonne. The best examples have not yet beennbsp;figured.

rock occurs near S�zanne in Southern France, and is of Eocene agef The plants were probably blown on to the freshly deposited carbonate of lime, or they may have simply fallen fromnbsp;the tree on to the incrusting matrix; more material was afterwards deposited and the flowers were completely enclosed.nbsp;Eventually the plant substance decayed, and as the matrixnbsp;hardened moulds were left of the vegetable fragments. Waxnbsp;was artiflcially forced into these cavities and the surroundingnbsp;substance removed by the action of an acid, and thus perfectnbsp;casts were obtained of Tertiary flowers.

Darwin has described the preservation of trees in Van Diemen�s land by means of calcareous substances. In speakingnbsp;of beds of blown sand containing branches and roots of treesnbsp;he says;

�The whole became consolidated by the percolation of calcareous matter; and the cylindrical cavities left by the decaying of the wood werenbsp;thus also filled up with a hard pseudo-stalactitical stone. The weather isnbsp;now wearing away the softer parts, and in consequence the hard casts ofnbsp;the roots and branches of the trees project above the surface, and, in anbsp;singularly deceptive manner, resemble the stumps of a dead thicket^.�

As a somewhat analogous method of preservation to that in travertine, the occurrence of plants in amber should benbsp;mentioned. In Eocene times there existed over a region, partnbsp;of which is now the North-east German coast, an extensivenbsp;forest of conifers and other trees. Some of the conifers werenbsp;rich in resinous secretions which were poured out fromnbsp;wounded surfaces or from scars left by falling branches. Asnbsp;these flowed as a sticky mass over the stem or collected onnbsp;the ground, flowers, leaves, and twigs blown by the wind ornbsp;falling from the trees, became embedded in the exuded resin.nbsp;Evaporation gradually hardened the resinous substance untilnbsp;the plant fragments became sealed up in a mass of amber,nbsp;in precisely the same manner in which objects are artificiallynbsp;preserved in Canada balsam. In many cases the amber acts asnbsp;a petrifying agent, and by penetrating the tissues of a piece ofnbsp;wood it preserves the minute structural details in wonderful

perfection*. Dr Thomas in an account of the amber beds of East Prussia in 1848, refers to the occurrence of large fossilnbsp;trees; he writes:

� The continuous changes to which the coast is exposed, often bring to light enormous trunks of trees, which the common people had longnbsp;regarded as the trunks of the amber tree, before the learned declared thatnbsp;they were the stems of palm trees, and in consequence determined thenbsp;position of Paradise to be on the coast of East Prussia 2.�

In 1887 an enormous fossil plant was discovered in a sandstone quarry at Clayton near Bradford�. The fossil wasnbsp;in the form of a sandstone cast of a large and repeatedlynbsp;branched Stigmaria, and it is now in the Owens College Museum,nbsp;where it was placed through the instrumentality of Profnbsp;Williamson. The plant was found spread out in its naturalnbsp;position on the surface of an arenaceous shale, and overlain bynbsp;a bed of hard sandstone identical with the material of whichnbsp;the cast is composed. Williamson has thus described thenbsp;manner of formation of the fossil;

�It is obvious that the entire base of the tree became encased in a plastic material, which was firmly moulded upon these roots whilst thenbsp;latter retained their organisation sufficiently unaltered to enable them tonbsp;resist all superincumbent pressure. This external mould then hardenednbsp;firmly, and as the organic materials decayed they were floated out bynbsp;water which entered the branching cavity ; at a still later period the samenbsp;water was instrumental in replacing the carbonaceous elements by thenbsp;sand of which the entire structure now consists'*.�

Although the branches have not been preserved for their whole length, they extend a distance of 29 feet 6 inches fromnbsp;right to left, and 28 feet in the opposite direction.

The fossil represented in fig. 1 (p. 10), from the collection of Dr John Woodward, affords a good example of a well-definednbsp;impression. The surface of the specimen, of which a cast isnbsp;represented in fig. 1, shows very clearly the characteristic

* For figures of fossil plants in amber, vide G�ppert and Berendt (45), Conwentz (90), Conwentz (96) amp;o.

�* Williamson (87) PI. xv. p. 45. A very fine specimen, similar to that in the Manchester Museum, has recently been added to the School of Mines Museumnbsp;in Berlin; Potoni� (90).

leaf-cushions and leaf-scars of a Lepidodendron. The stem was embedded in soft sand, and as the latter became hard andnbsp;set, an impression was obtained of the external markings ofnbsp;the Lepidodendron. Decay subsequently removed the substancenbsp;of the plant.

In fig. 11 some upright stems of a fossil Horse-tail {Equisetites columnaris) from the Lower Oolite rocks near Scarborough, are seen in a vertical position in sandstone. On the surface ofnbsp;the fossils there is a thin film of carbonaceous matter, which isnbsp;all that remains of the original plant substance ; the stems werenbsp;probably floated into their present position and embedded vertically in an arenaceous matrix. The hollow pith-cavity wasnbsp;filled with sand, and as the tissues decayed they became in partnbsp;converted into a thin coaly layer. The vertical position ofnbsp;such stems as those in fig. 11 naturally suggests their preservation in situ, but in this as in many other cases the erectnbsp;manner of occurrence is due to the settling down of the driftednbsp;plants in this particular position.

the formation of castsh The outer surface with the characteristic spirally arranged circular depressions, represents the wrinklednbsp;bark of the dried plant; the smaller cylinder, on the left sidenbsp;of the upper end (fig. 12, 2, p), marks the position of the pith

surrounded by the secondary wood, which has been displaced from its axial position. The pith decayed first, and the spacenbsp;was filled in with mud; somewhat later the wood and cortexnbsp;were partially destroyed, and the rod of material which hadnbsp;been introduced into the pith-cavity dropped towards one sidenbsp;of the decaying shell of bark.

As the parenchymatous medullary rays readily decayed, the mud in the pith extended outwards between the segments ofnbsp;wood which still remained intact, and so spokes of argillaceousnbsp;material were formed which filled the medullary ray cavities.nbsp;The cortical tissues were decomposed, and their place takennbsp;by more argillaceous material. At one end of the specimennbsp;(fig. 12, 3) we find the wood has decayed without its place beingnbsp;afterwards filled up with foreign material. At the opposite

r The British Museum collection contains a specimen of Stigmaria preserved in the same manner as the example shown in fig. 12.

end of the specimen, the woody tissue has been partially preserved by the infiltration of a solution containing carbonate of lime (fig. 12, 2).

Numerous instances have been recorded from rocks of various geological ages of casts of stems standing erect andnbsp;at right angles to the bedding of the surrounding rock. Thesenbsp;vertical trees occasionally attain a considerable length, andnbsp;have been formed by the filling in by sand or mud of a pipe leftnbsp;by the decay of the stem. It is frequently a matter of some difficulty to decide how far such fossils are in the position of growthnbsp;of the tree, or whether they are merely casts of drifted stems,nbsp;which happen to have been deposited in. an erect position. Thenbsp;weighting of floating trees by stones held in the roots, addednbsp;to the greater density of the root wood, has no doubt often beennbsp;the cause of this vertical position. In attempting to determinenbsp;if an erect cast is in the original place of growth of the tree, it isnbsp;important to bear in mind the great length of time that wood isnbsp;able to resist decay, especially under water. The wonderfulnbsp;state of preservation of old piles found in the bed of a river,nbsp;and the preservation of wooden portions of anchors of which thenbsp;iron has been completely removed by disintegration, illustratenbsp;this power of resistance. In this connection, the followingnbsp;passage from Lyell�s travels in America is of interest. Innbsp;describing the site of an old forest, he writes^:

� Some of the stumps, especially those of the fir tribe, take fifty years to rot away, though exposed in the air to alternations of rain andnbsp;sunshine, a fact on which every geologist will do well to reflect, for itnbsp;is clear that the trees of a forest submerged beneath the water, or stillnbsp;more, if entirely excluded from the air, by becoming imbedded in sediment,nbsp;may endure for centuries without decay, so that there may have beennbsp;ample time for the slow petrifaction of erect fossil trees in the Carboniferous and other formations, or for the slow accumulation aroundnbsp;them of a great succession of strata.�

In another place, in speaking of the trees in the Great Dismal Swamp, Lyell writes:��When thrown down, they arenbsp;soon covered by water, and keeping wet they never decompose,nbsp;except the sap wood, which is less than an inch thick We

see, then, that trees may have resisted decay for a sufficiently long time to allow of a considerable deposition of sediment. Itnbsp;is very difficult to make any computation of the rate of deposition of a particular set of sedimentary strata, and, therefore, tonbsp;estimate the length of time during which the fossil stems mustnbsp;have resisted decay.

The protective qualities of humus acids, apart from the almost complete absence of Bacteria* from the waters of Moor-or Peat-land, is a factor of great importance in the preservationnbsp;of plants against decay for many thousands of years.

From examples of fossil stems or leaves in which the organic material has been either wholly or in part replaced by coal, wenbsp;may pass by a gradual transition to a mass of opaque coal innbsp;which no plant structure can be detected. It is by no meansnbsp;uncommon to notice on the face of a piece of coal a distinctnbsp;impression of a plant stem, and in some cases the coal isnbsp;obviously made up of a number of flattened and compressednbsp;branches or leaves of which the original tissues have beennbsp;thoroughly carbonised. A block of French coal, representednbsp;in fig. 13, consists very largely of laminated bands composednbsp;of the long parallel veined leaves of the genus Cordaitesnbsp;and of the bark of Lepidodeyidron, Sigillaria, and other Coal-Measure genera. The long rhizomes and roots below the coalnbsp;are preserved as casts in the underclay.

In examining thin sections of coal, pieces of pitted tracheids or crushed spores are frequently met with as fragments ofnbsp;plant structures which have withstood decay more effectuallynbsp;than the bulk of the vegetable d�bris from which the coal wasnbsp;formed.

The coaly layer on a fossil leaf is often found to be without any trace of the plant tissues, but not infrequentlynbsp;such carbonised leaves, if treated with certain reagents andnbsp;examined microscopically, are seen to retain the outlines of thenbsp;epidermal cells of the leaf surface. If a piece of the Carbonaceous film detached from a fossil leaf is left for some days innbsp;a small quantity of nitric acid containing a crystal of chlorate ofnbsp;potash, and, after washing with water, is transferred to ammonia,nbsp;* Warming (96) p. 170.

transparent film often shows very clearly the outlines of the epidermal cell and the form of the stomata. Such treatmentnbsp;has been found useful in many cases as an aid to determination�.

Prof. Zeiller informs me that he has found it particularly satisfactory in the case of cycadean leaves.

It is sometimes possible to detach the thin lamina repre-1 Bornemann (56), Schenk (67), Zeiller (82).

senting the carbonised leaf or other plant fragment from the rock on which it lies and to mount it whole on a slide. Goodnbsp;examples of plants treated in this way may be seen in thenbsp;Edinburgh and British Museums, especially Sphenopteris frondsnbsp;from the Carboniferous oil shales of Scotland. In the excellentnbsp;collection of fossil plants in Stockholm there are still finernbsp;examples of such specimens, obtained by Dr Nathorst fromnbsp;some of the Triassic plants of Southern Sweden. In a few instances the tissues of a plant have been converted into coal in suchnbsp;a manner as to retain the form of the individual cells, whichnbsp;appear in section as a black framework in a lighter colourednbsp;matrix. Examples of such carbonised tissues were figured bynbsp;some of the older writers, and Solms-Laubach has recently�'nbsp;described sections of Palaeozoic plants preserved in thisnbsp;manner. The section represented in fig. 70 is that of a Calamitenbsp;stem (8 X 9'5 cm.) in which the wood has been converted intonbsp;carbonaceous material, but the more delicate tissues have beennbsp;almost completely destroyed. The thin and irregular blacknbsp;line a little distance outside the ring of wood, and formingnbsp;the limit of the drawing, probably represents the cuticle. Thenbsp;whole section is embedded in a homogeneous matrix of calcareous rock, in which the more resistant tissues of the plantnbsp;have been left as black patches and faint lines.

Mention should be made of a special form of preservation which has been described as fossilisation in half-relief. If anbsp;stem is imbedded in sand or mud, the matrix receives an impression of the plant surface, and if the hollow pith-cavity isnbsp;filled with the surrounding sediment, the surface of the medullary cast will exhibit markings different from those seen on thenbsp;surface in contact with the outside of the stem. The spacenbsp;separating the pith-cast from the mould bearing the impressionnbsp;of the stem surface may remain empty, or it may be filled withnbsp;sedimentary material. In half-relief fossils, on the other hand,nbsp;we have projecting from the under surface of a bed a more ornbsp;less rounded and prominent ridge with certain surface markings,nbsp;and fitting into a corresponding groove in the underlying rocknbsp;on which the same markings have been impressed. It isnbsp;1 Solms-Laubach (95^).

conceivable that such a cast might be obtained if soft plant fragments were lying on a bed of sand, and were pressednbsp;into it by the weight of superincumbent material. The plantnbsp;fragment would be squeezed into a depression, and its substancenbsp;might eventually be removed and leave no other trace than thenbsp;half-relief cast and hollow mould. A twig lying on sand wouldnbsp;by its own weight gradually sink a little below the surface; ifnbsp;it were then blown away or in some manner removed, thenbsp;depression would show the surface features of the twig. Whennbsp;more sand came to be spread out over the depression, it wouldnbsp;find its way into the pattern of the mould, and so produce anbsp;cast. If at a later period when the sand had hardened, thenbsp;upper portion were separated from the lower, from the formernbsp;there would project a rounded cast of the hollow mould.nbsp;The preservation of soft algae as half-relief casts has beennbsp;doubted by Nathorst^ and others as an unlikely occurrence innbsp;nature. They prefer to regard such ridges on a rock face as thenbsp;casts of the trails or burrows of animals. This question of thenbsp;preservation of the two sides of a mould showing the same impression of a plant has long been a difficult problem; it is discussednbsp;by Parkinson in his Organic Remains. In one of the lettersnbsp;(No. XLVi), he quotes the objection of a sceptical friend, whonbsp;refuses to believe such a manner of preservation possible,nbsp;� until,� says Parkinson, � I can inform him if, by involving anbsp;guinea in plaster of Paris, I could obtain two impressions of thenbsp;king�s head, without any impression of the reverse^.�

It would occupy too much space to attempt even a brief reference to the various materials in which impressions of plantsnbsp;have been preserved. Carbonaceous matter is the most usualnbsp;substance, and in some cases it occurs in the form of graphitenbsp;which on dark grey or black rocks has the appearance of a plantnbsp;drawn in lead pencil. The impressions of plants on the Jurassicnbsp;(Kimeridgian) slates of Solenhofen� in Bavaria, like those onnbsp;the Triassic sandstones of the Vosges, are usually marked out innbsp;red iron oxide.

3 nbsp;nbsp;nbsp;The British Museum collection contains many good examples of the Solen-hofen plants.

So far we have chiefly considered examples of plants preserved in various ways by incrustation, that is, by having been enclosed in some medium which has received an impression of thenbsp;surface of the plant in contact with it. By far the most valuablenbsp;fossil specimens from a botanical point of view are howevernbsp;those in which the internal structure has been preserved; thatnbsp;is in which the preserving medium has not served merely as annbsp;encasing envelope or internal cast, but has penetrated into thenbsp;body of the plant fragment and rendered permanent thenbsp;organization of the tissues. In almost every Natural Historynbsp;or Geological Museum one meets with specimens of petrifiednbsp;trees or polished sections of fossil palm stems and other plants,nbsp;in which the internal structure has been preserved in siliceousnbsp;material, and admits of detailed investigation in thin sectionsnbsp;under the microscope. Silica, calcium carbonate, with usuallynbsp;a certain amount of carbonate of iron and magnesium carbonate,nbsp;iron pyrites, amber, and more rarely calcium fluoride or othernbsp;substances have taken the place of the original cell-walls. Ofnbsp;silicified stems, those from Antigua, Egypt, Central France,nbsp;Saxony, Brazil, Tasmania k and numerous other places afford goodnbsp;examples. Darwin records numerous silicified stems in Northernnbsp;Chili, and the Uspallata Pass. In the central part of the Andesnbsp;range, 7000 feet high, he describes the occurrence of �Snow-white projecting silicified columns...They must have grown,� henbsp;adds, � in volcanic soil, and were subsequently submerged belownbsp;sea-level, and covered with sedimentary beds and lava-flows^.�nbsp;A striking example of the occurrence of numerous petrifiednbsp;plant stems has been described by Holmes from the Tertiarynbsp;forests of the Yellowstone Park. From the face of a cliff onnbsp;the north side of Ameythryst mountain � rows of upright trunksnbsp;stand out on the ledges like the columns of a ruined temple.nbsp;On the more gentle slopes farther down, but where it is still toonbsp;steep to support vegetation, save a few pines, the petrifiednbsp;trunks fairly cover the surface, and were at first supposed by usnbsp;to be the shattered remains of a recent forestMarsh^ and

1 nbsp;nbsp;nbsp;There is a splendid silicified tree stem from Tasmania of Tertiary agenbsp;several feet in height in the National Museum.

2 nbsp;nbsp;nbsp;Darwin (90) p. 317.nbsp;nbsp;nbsp;nbsp;� Holmes (80) p. 126, fig. 1.nbsp;nbsp;nbsp;nbsp;^ Marsh (71).

Conwentz^ have described silicified trees more than fifty feet in length from a locality in California where several large forestnbsp;trees of Tertiary age have been preserved in volcanic strata.nbsp;In South Africa on the Drakenberg hills there occur numerousnbsp;silicified trunks, occasionally erect and often lying on thenbsp;ground, probably of Triassic age I In some instances thenbsp;specimens measure several feet in length and diameter. Somenbsp;of the coniferous stems seen in Portland, and occasionally metnbsp;with reared up against a house side, illustrate the silicification ofnbsp;plant structure on a large scale. These are of Upper Jurassicnbsp;(Purbeck) age. From Grand�Croix in France a silicified stemnbsp;of Cordaites of Palaeozoic age has been recorded with a lengthnbsp;of twenty meters. The preservation of plants by siliceous infiltrations has long been known. One of the earliest descriptionsnbsp;of this form of petrifaction in the British Isles is that of stemsnbsp;found in Lough Neagh, Ireland. In his lectures on Naturalnbsp;Philosophy, published at Dublin in 1751, Barton gives severalnbsp;figures of Irish silicified wood, and records the followingnbsp;occurrence in illustration of the peculiar properties erroneouslynbsp;attributed to the waters of Lough Neagh. Describing a certainnbsp;specimen (No. xxvi), he writes:�

�This is a whetstone, which as Mr Anthony Shane, apothecary, who was born very near the lake, and is now alive, relates, he made by puttingnbsp;a piece of holly in the water of the lake near his father�s house, and fixingnbsp;it so as to withstand the motion of the water, and marking the place so asnbsp;to distinguish it, he went to Scotland to pursue his studies, and sevennbsp;years after took up a stone instead of holly, the metamorphosis havingnbsp;been made in that time. This account he gave under his handwriting.nbsp;The shore thereabouts is altogether loose sand, and two rivers dischargenbsp;themselves into the lake very near that placed.�

The well-known petrified trees from the neighbourhood of Lough Neagh are probably of Pliocene age, but their exactnbsp;source has been a matter of disputequot;*.

In 1836 Stokes described certain stems in which the tissues had been partially mineralised. In describing a specimen of

A large piece from one of these South African trees is in the Fossil-plant Gallery of the British Museum.nbsp;nbsp;nbsp;nbsp;,

� The wood is, for the most part, in the state of very old dry wood, but there are several insulated portions, in which the place of the wood hasnbsp;been taken by carbonate of lime. These portions, as seen on the surfacenbsp;of the horizontal section, are irregularly circular, varying in size, butnbsp;generally a little less or more than j of an inch in diameter, and theynbsp;run through the whole thickness of the specimen in separate, perpendicularnbsp;columns. The vessels of the wood are distinctly visible in the carbonatenbsp;of lime, and are more perfect in their form and size in those portions ofnbsp;the specimen than in that which remains unchanged i.�

This partial petrifaction of the structure in patches is often met with in fossil stems, and may be seriously misleadingnbsp;to those unfamiliar with the appearance presented by thenbsp;crystallisation of silica from scattered centres in a mass ofnbsp;vegetable tissue. A good example of this is afforded by thenbsp;gigantic stems discovered in 1829 in the Craigleith Quarry nearnbsp;Edinburgh^. Of those two large stems foiind in the Sandstonenbsp;rock, the longest, originally 11 meters long and S'S�3 9 metersnbsp;in girth, is now set up in the grounds of the British Museum,nbsp;and a large polished section (1 m. x 87 cm.) is exhibited in the

Araucarioxylon Withami (L. and H.). Radiating lines of crystallisation in secondary wood, as seen in transverse section.

B. Lepidodendron sp. Concentric lines of crystallisation, and scalariform tracheids, as seen in longitudinal section.

Fossil-plant Gallery. The other stem is in the Botanic Garden, Edinburgh. Transverse sections of the wood of the Londonnbsp;^ Stokes (40) p. 207.nbsp;nbsp;nbsp;nbsp;^ Witham (31), Christison (76).

specimen show scattered circular patches (fig. 14 A) in the mineralised wood in which the tracheids are very clearly preserved ; while in the other portion the preservation is much lessnbsp;perfect. The patch of tissue in fig. 14 A shows a portion ofnbsp;the wood of the Craigleith tree [Araucarioxylon Withami (L.nbsp;and H.)] in which the mineral matter, consisting of dolomitenbsp;with a little silica here and there, has crystallised in such a

manner as to produce what is practicallj^ a cone-in-cone structure on a small scale, which has partially obliterated the

ance to that described by Cole' in certain minerals. The crystallisation has been set up along lines radiating fromnbsp;different centres, and the particles of the tissue have beennbsp;pushed as it were along these lines.

A somewhat different crystallisation phenomenon is illustrated by the extremely fine section of a Lepidodendroid plant shown in fig. 15. The tissues of the primary and secondarynbsp;wood and of) are well preserved throughout in silica, butnbsp;scattered through the siliceous matrix there occur numerousnbsp;circular patches, as seen in the figure. One of these is morenbsp;clearly shown in fig. 14 B drawn from a longitudinal sectionnbsp;through the secondary wood, ; it will be noticed that wherenbsp;the concentric lines of the circular patch occur, the scalariformnbsp;thickenings of the tracheids are sharply defined, but immediately a tracheid is free of the patch these details are lost. Itnbsp;would appear that in this case silicification was first completednbsp;round definite isolated centres, and the secondary crystallisationnbsp;in the matrix partially obliterated some of the more delicatenbsp;structural features. The same phenomenon has been observednbsp;in oolitic rocksquot;, in which the oolitic grains have resistednbsp;secondari^ crystallisation and so retained their original structure.

Among the most important examples of silicified plants are those from a few localities in Central France. In the neighbourhood of Autim there used to be found in abundance loose nodulesnbsp;of siliceous rock containing numerous fragments of seeds, twigs,nbsp;and leaves of different plants. The rock of which the brokennbsp;portions are found on the surface of the ground was formednbsp;about the close of the Carboniferous period.

At the hands of French investigators the microscopic examination of these fragments of a Palaeozoic vegetation havenbsp;thrown a flood of light on the anatomical structure of manynbsp;extinct types. Sometimes the silica has penetrated the cavitiesnbsp;of the cells and vessels, and the walls have decayed withoutnbsp;their substance being replaced by mineral material. Sectionsnbsp;of tissues preserved in this manner, if soaked in a colourednbsp;1 Cole (94), figs. 1 and 3.nbsp;nbsp;nbsp;nbsp;- Harker (95) p. 233, fig. 56.

solution assume an appearance almost identical with that of stained sections of recent plants. The spaces left by thenbsp;decayed walls act as fine capillaries and suck up the colourednbsp;solution f

In the Coal-Measure sandstones of England large pieces of woody stems are occasionally met with innbsp;which the mineralisation has been incomplete. A brown piece of fossil stem lyingnbsp;in a bed of sandstone shows on thenbsp;surface a distinct woody texture, and thenbsp;lines of wood elements are clearly visible.

The whole is, however, very friable and falls to pieces if an attempt is made tonbsp;cut thin sections of it; the tracheids ofnbsp;the wood easily fall apart owing to thenbsp;walls being imperfectly preserved, andnbsp;the absence of a connecting frameworknbsp;such as would have been formed had thenbsp;membranes been thoroughly silicified.

It is occasionally possible to obtain from petrified plant stems perfect casts innbsp;silica or other substances of the cavitynbsp;of a sclerenchymatous fibre, in which thenbsp;mineral has been deposited not only innbsp;the cavity but in the fine pit-canalsnbsp;traversing the lignified walls. Such a castnbsp;is represented in fig. 16, the fine lateralnbsp;projections are the delicate casts of thenbsp;pit canals. Numerous instances of minutenbsp;and delicate tissues preserved in silica arenbsp;recorded in later chapters. A somewhatnbsp;unusual type of silicification is met with in some of thenbsp;Gondwana rocks of India, in which cycadean fronds occur asnbsp;white porcellaneous specimens showing a certain amount ofnbsp;internal structure in a siliceous matrix. Specimens of suchnbsp;leaves may be seen in the British Museum.

^ I am indebted to Dr Renault of Paris for showing to me several preparations illustrating this method of petrifaction.

In the Coal-Measures of England, especially in the neigh-, bourhood of Halifax in Yorkshire, and in South Lancashire, thenbsp;seams of coal occasionally contain calcareous nodules varying innbsp;size from a nut to a man�s head, and consisting of about 70 �/o ofnbsp;carbonate of calcium and magnesium, and 30 �/o of oxide of iron,nbsp;sulphide of iron, amp;c.^ The nodules, often spoken of by Englishnbsp;writers as � coal-balls,� contain numerous fragments of plants innbsp;which the minute cellular structure is preserved with remarkable perfection. It should be noted that the term coal-ballnbsp;is also applied to rounded or subangular pieces of coal whichnbsp;are occasionally met with in coal seams, and especially in

certain French coal heids. To avoid' confusion it is better to speak of the plant-containing nodules as calcareous nodules,nbsp;restricting the term coal-ball to true coal pebbles. A sectionnbsp;1 Cash and Hioh (78).

of a calcareous nodule, when seen under the microscope, presents the appearance of a matrix of a crystalline calcareous substancenbsp;containing a heterogeneous mixture of all kinds of plant tissues,nbsp;usually in the form of broken pieces and in a confused mass.

A large section of one of these nodules (IS'� cm. x 8'5 cm.) is shown in fig. 17. It illustrates the manner of occurrence ofnbsp;various fragments of different plants in which the structurenbsp;has been more or less perfectly preserved. In this particularnbsp;example we see sections of Myeloxylon (I), Calamites (II), Fernnbsp;petioles (Rachiopteris) (III), Stigmarian appendages (IV),nbsp;Lepidodendroid leaves (V), Myeloxylon pinnules (VI), Gymno-spermous seeds (VII), Twig of a Lepidodendron, showing thenbsp;central xylem cylinder and large leaf-bases on the outer cortex,nbsp;(VIII), Sporangia and spores of a strobilus (IX), Tangentialnbsp;section of a Myeloxylon petiole (X), Rachiopteris sp. (XI),nbsp;Rachiopteris sp. (XII), Band of sclerenchymatous tissue (XIII),nbsp;Rachiopteris sp. (XIV).

The general appearance of a calcareous plant-nodule suggests a soft pulpy mass of decaying vegetable debris, through whichnbsp;roots were able to bore their way, as in a piece of peat or leafynbsp;mould. Overlying this accumulation of soft material therenbsp;was spread out a bed of muddy sediment containing numerousnbsp;calcareous shells, which supplied the percolating water withnbsp;the material which was afterwards deposited in portions ofnbsp;the vegetable d�bris. According to this view the calcareousnbsp;nodules of the coal seams represent local patches of a widespread mass of d�bris which were penetrated by a carbonatednbsp;solution, and so preserved as samples of a decaying mass ofnbsp;vegetation, of which by far the greater portion becamenbsp;eventually converted into coal\

In such nodules, we find that not only has the framework of the tissues been preserved, but frequently the remains of cellnbsp;contents are clearly seen. In some cases the cells of a tissue maynbsp;contain in each cavity a darker coloured spot, which is probablj^nbsp;the mineralised cell nucleus. (Fig. 42, A, 1, p. 214.) Thenbsp;contents of secretory sacs, such as those containing gum or resin,nbsp;are frequently found as black rods filling up the cavity of the cell

or canal. The contents of cells in some cases closely simulate starch grains, and such may have been actually present in thenbsp;tissues of a piece of a fossil dicotyledonous stem described bynbsp;Thiselton-Dyer from the Lower Eocene Thanet bedsh and innbsp;the rhizome of a fossil Osmimda recorded by Carruthers^.nbsp;(Fig. 42, B, p. 214.)

Schultze in 1855* recorded the discovery of cellulose by microchemical tests applied to macerated tissue from Tertiarynbsp;lignite and coal. With reference to the possibility of recc)gnisingnbsp;cell contents in fossil tissue it is interesting to find thatnbsp;Dr Murray of Scarborough had attempted, and apparentlynbsp;with success, to apply chemical tests to the tissues of Jurassicnbsp;leaves. In a letter written to Hutton in 1833 Murray speaksnbsp;of his experiments as follows

� Reverting to the Oolitic plants, I have again and with better success been experimenting u2ron the thin transparent films of leaves, chieflynbsp;of Taeniopteris vittata and Cyclopteru, which from their tenuity offer fine

among the filmy leaves of the Fucoides of A. Bronguiart for iodine, but hitherto without success, and indeed can hardly expect it, as probably didnbsp;iodine exist in them, it must have long ago entered into new com-binationsh�

Apart from this difficulty, it is not surprising that Dr Murray�s search for iodine was unsuccessful, consideringnbsp;how little algal nature most of the so-called Fucoids possess.

Some of the most perfectly preserved tissues as regards the details of cell contents are those Of gymnospermous seeds fromnbsp;Autun. In sections of one of these seeds which I recently hadnbsp;the opportunity of examining in Prof. Bertrand�s collection, thenbsp;parenchymatous cells contained very distinct nuclei and protoplasmic contents. In one portion of the tissue in the nucellus ofnbsp;Sphaerospermiun the cell walls had disappeared, but the nucleinbsp;remained in a remarkable state of preservation. The cellsnbsp;shown in fig. 42 are from the ground tissue of a petiole of

1 Thiselton-Dyer (72) PI. vi. * Carruthers (70). nbsp;nbsp;nbsp;* Schultze (55),

** I am indebted to Prof. Lebour of the Durham College of Science for the loan of this letter.

Cycadeoidea gigantea Sew.\ a magnificent Cycadean stem from Portland recently added to the British Museum collection; innbsp;the cell A, 1, the nucleus is fairly distinct and in 2 and 4 thenbsp;contracted cell-contents is clearly seen. Other interestingnbsp;examples of fossil nuclei are seen in a Lyginodendron leafnbsp;figured by Williamson and Scott in a recent Memoir on thatnbsp;genus I Each mesophyll cell contains a single dark nucleus.nbsp;The mineralisation of the most delicate tissues and thenbsp;preservation of the various forms of cell-contents are nownbsp;generally admitted by those at all conversant with the possibilities of plant petrifaction. If we consider what these factsnbsp;mean�the microscopic investigation of not only the finestnbsp;framework but even the very life-substance of Palaeozoicnbsp;plants�we feel that the aeons since the days when thesenbsp;plants lived have been well-nigh obliterated.

Occasionally the plant tissues have assumed a black and somewhat ragged appearance, giving the impression of charrednbsp;wood. A section of a recent burnt piece of wood resembles verynbsp;closely some of the fossil twigs from the coal seam nodules. Itnbsp;is possible that in such cases we have portions of mineralisednbsp;tissues which were first burnt in a forest fire or by lightningnbsp;and then infiltrated with a petrifying solution. An example ofnbsp;one of these black petrified plants is shown in fig. 74 B. Chap. x.nbsp;In many of the fossil plants there are distinct traces of fungusnbsp;or bacterial ravages, and occasionally the section of a piece ofnbsp;mineralised wood shows circular spaces or canals which have thenbsp;appearance of being the work of some wood-eating animal, andnbsp;small oval bodies sometimes occur in such spaces which maynbsp;be the coprolites of the xylophagous intruder. (Fig. 24, p. 107.)

It is well known to geologists that during the Permian and Carboniferous periods the southern portion of Scotland was thenbsp;scene of widespread volcanic activity. Forests were overwhelmednbsp;by lava-streams or showers of ash, and in some districts treenbsp;stems and broken plant fragments became sealed up in a volcanicnbsp;matrix. Laggan Bay in the north-east corner of the Isle ofnbsp;Arran, and Petticur a short distance from Burntisland on thenbsp;north shore of the Firth of Forth, are two localities wherenbsp;1 Seward (97).nbsp;nbsp;nbsp;nbsp;^ Williamson and Scott (96) PI. xxiv. fig. 16.

petrified plants of Carboniferous age occur in such preservation as allows of a minute investigation of their internal structure.nbsp;The occurrence of plants in the former locality was first discoverednbsp;by Mr Wilnsch of Glasgow; the fossils occur in association withnbsp;hardened shales and beds of ash, and are often exceedingly wellnbsp;preserved ^ In fig. 18 is reproduced a sketch of a hollow treenbsp;trunk from Arran, probably a Lepidodendron stem, in whichnbsp;only the outer portion of the bark has been preserved, whilenbsp;the inner cortical tissues have been removed and the spacenbsp;occupied by volcanic detritus.

The smaller cylindrical structures in the interior of the hollow trunk are the central woody cjdinders of Lepidodendroidnbsp;trees; each consists of an axial pith surrounded by a band

of primary wood and a broader zone of secondary wood. One of the axes probably belonged to the stem of which only thenbsp;shell has been preserved, the others must have come from other

trees and may have been floated in by watert The microscopic details of the wood and outer cortex have in this instance beennbsp;preserved in a calcareous material, which was no doubt derivednbsp;by water'percolating through the volcanic ash. It is frequentlynbsp;found that in fossil trees or twigs a separation of the tissuesnbsp;has taken place along such natural lines of weakness as thenbsp;cambium or the phellogen, before the petrifying medium hadnbsp;time to permeate the entire structure. Tree stems recentlynbsp;killed by lava streams during volcanic eruptions at the presentnbsp;day supply a parallel with the Palaeozoic forest trees ofnbsp;Carboniferous times.

Guillemard in describing a volcanic crater in Celebes, speaks of burnt trees still standing in the lava stream, � so charred at thenbsp;base of the trunk that we could easily push them down^.� Annbsp;interesting case is quoted by Hooker in his Himalayan Journals,nbsp;illustrating the occurrence of a hollow shell of a tree, in whichnbsp;the outer portions of a stem had been left while the innernbsp;portions had disappeared, the wood being hollow and so favourable to the production of a current of air which acceleratednbsp;the destruction of the internal tissues.

On the coast near Burntisland on the Firth of Forth blocks of rock are met with in which numerous plant fragments ofnbsp;Carboniferous age are scattered in a confused mass through anbsp;calcareous volcanic matrix. The twigs, leaves, spores, and othernbsp;portions are in small fragments, and their delicate cells arenbsp;often preserved in wonderful perfection.

The manner of occurrence of plants in sandstones, shales or other rocks is often of considerable importance to thenbsp;botanist and geologist, as an aid to the correct interpretationnbsp;of the actual conditions which obtained at the time when thenbsp;plant remains were accumulating in beds of sediment. Tonbsp;attempt to restore the conditions under which any set of plantsnbsp;became preserved, we have to carefully consider each specialnbsp;case. A nest of seeds preserved as internal casts in a mass ofnbsp;sandstone, such as is represented by the block of Carboniferousnbsp;sandstone in fig. 19, suggests a quiet spot in an eddy where

1 An erroneous interpretation of the Arran steins is given in LyelTs Elements of Geology : Lyell (78) p. 347.nbsp;nbsp;nbsp;nbsp;^ Guillemard (86) p. 322.

seeds were deposited in the sandy sediment. Delicate leaf structures with sporangia still intact, point to quietly flowingnbsp;water and a transport of no great distance. Occasionally the

Fio. 19. Piece of Coal-Measures Sandstone with casts of Trigonocarpon seeds, from Peel Quarry near Wigan. Erom a specimen in the Manchesternbsp;Museum, Owens College. J nat. size.

large number of delicate and light plant fragments, associated it may be with insect wings, may favour the idea of a windnbsp;storm which swept along the lighter pieces from a forest-cladnbsp;slope and deposited them in the water of a lake. In somenbsp;Tertiary plant-beds the manner of occurrence of leaves andnbsp;flowers is such as to suggest a seasonal alternation, and thenbsp;different layers of plant debris may be correlated with definitenbsp;seasons of growth!

The predominance of certain classes of plants in a particular bed may be due to purely mechanical causes and to differentialnbsp;sorting by water, or it may be that the district traversed by thenbsp;stream which carried down the fragments was occupied almostnbsp;exclusively by one set of plants. The trees from higher groundnbsp;may be deposited in a different part of a river�s course to thosenbsp;growing in the plains or lowland marshes. It is obviouslynbsp;impossible to lay down any definite rules as to the reading ofnbsp;plant records, as aids to the elucidation of past physical andnbsp;botanical conditions. Each case must be separately considered,nbsp;and the various probabilities taken into account, judging bynbsp;reference to the analogy of present day conditions.

to imitate the natural processes of plant mineralisation*. By soaking sections of wood for some time in different solutions,nbsp;and then exposing them to heat, the organic substance of thenbsp;cell walls has been replaced by a deposit of oxide of iron andnbsp;other substances. Fern leaves heated to redness between piecesnbsp;of shale have been reduced to a condition very similar to that ofnbsp;fossil fronds. Pieces of wood left for centuries in disused minesnbsp;have been found in a state closely resembling ligniteAttemptsnbsp;have also been made to reproduce the conditions under whichnbsp;vegetable tissues were converted into coal, but as yet thesenbsp;have not yielded results of much scientific value. The Geysersnbsp;of Yellowstone Park have thrown some light on the manner innbsp;which wood may be petrified by the percolation of siliceous solutions ; and it has been suggested that the silicification of plantsnbsp;may have been effected by the waters of hot springs holdingnbsp;silica in solution. Examples of wood in process of petrifactionnbsp;in the Geyser district of North America have been recorded bynbsp;Kuntze^, and discussed by Schweinfurth^, Solms-Laubach*nbsp;and others�. The latter expresses the opinion that by a longnbsp;continuance of such action as may now be observed in thenbsp;neighbourhood of hot springs, the organic substance of woodnbsp;might be replaced by siliceous material. The exact manner ofnbsp;replacement needs more thorough investigation. Kuntze describes the appearance of forest trees which have been reachednbsp;by the waters of neighbouring Geysers. The siliceous solutionnbsp;rises in the wood by capillarity; the leaves, branches and barknbsp;are gradually lost, and the outer tissues of the wood becomenbsp;hardened and petrified as the result of evaporation from thenbsp;exposed surface of the stem. The products of decay going onnbsp;in the plant tissues must be taken into account, and the doublenbsp;decomposition which might result. There is no apparent reasonnbsp;why experiments undertaken with pieces of recent wood exposed to permeation by various calcareous and siliceous solutionsnbsp;under different conditions should not furnish useful results.

^ G�ppert (36), etc. nbsp;nbsp;nbsp;^ Hirsohwald (73).nbsp;nbsp;nbsp;nbsp;^ Kuntze (80) p. 8.

� G�ppert (57). Some of the large silioified trees mentioned by G�ppert may be seen in the Breslau Botanic gardens.

CHAPTER V.

� Robinson Crusoe did not feel bound to conclude, from the single human footprint which he saw in the sand, that the maker of thenbsp;impression had only one leg.�

The student of palaeobotany has perhaps to face more than his due share of difficulties and fruitful sources of error; butnbsp;on the other hand there is the compensating advantage thatnbsp;trustworthy conclusions arrived at possess a special value.nbsp;While always on the alert for rational explanations of obscurenbsp;phenomena by means of the analogy supplied by existingnbsp;causes, and ready to draw from a wide knowledge of recentnbsp;botany, in the interpretation of problems furnished by fossilnbsp;plants, the palaeobotanist must be constantly alive to thenbsp;necessity for cautious statement. That there is the greatestnbsp;need of moderation and safe reasoning in dealing with thenbsp;botanical problems of past ages, will be apparent to anyonenbsp;possessing but a superficial acquaintance with fossil plantnbsp;literature. The necessity for a botanical and geological trainingnbsp;has already been referred to in a previous chapter.

It would serve no useful purpose, and would occupy no inconsiderable space, to refer at length to the numerous mistakesnbsp;which have been committed by experienced writers on thenbsp;subject of fossil plants. Laymen might find in such a list ofnbsp;blunders a mere comedy of errors, but the palaeobotanist must

see in them serious warnings against dogmatic conclusions or expressions of opinion on imperfect data and insufficient evidence.nbsp;The description of a fragment of a handle of a Wedgewoodnbsp;teapot as a curious form of Calamite^ and similar instances ofnbsp;unusual determinations need not detain us as examples ofnbsp;instructive errors. The late Prof. Williamson has on more thannbsp;one occasion expressed himself in no undecided manner as tonbsp;the futility of attempting to determine specific forms amongnbsp;fossil plants, without the aid of internal structure^; and even innbsp;the case of well-preserved petrifactions he always refused tonbsp;commit himself to definite specific diagnoses. In his remarks innbsp;this connection, Williamson no doubt allowed himself to expressnbsp;a much needed warning in too sweeping language. It is one ofnbsp;the most serious drawbacks in palaeobotanical researches thatnbsp;in the majority of cases the specimens of plants are bothnbsp;fragmentary and without any trace of internal structure.nbsp;Specimens in which the anatomical characters have been preserved necessarily possess far greater value from the botanist�snbsp;point of view than those in which no such petrifaction hasnbsp;occurred. On the other hand, however, it is perfectly possiblenbsp;with due care to obtain trustworthy and valuable results fromnbsp;the examination of structureless casts and impressions. Innbsp;dealing with the less promising forms of plant fossils, there isnbsp;in the first place the danger of trusting to superficial resemblance.nbsp;Hundreds of fossil plants have been described under the namesnbsp;of existing genera on the strength of a supposed agreement innbsp;external form; but such determinations are very frequently notnbsp;only valueless but dangerously misleading. Unless the evidence is of the best, it is a serious mistake to make usenbsp;of recent generic designations. If we consider the difficultiesnbsp;which would attend an attempt to determine the leaves,nbsp;fragments of stems and other detached portions of variousnbsp;recent genera, we can better appreciate the greater probabilitynbsp;of error in the case of imperfectly preserved fossil fragments.

The portions of stems represented in figures 20 and 21, exhibit a fairly close resemblance to one another; in the absence

E. nbsp;nbsp;nbsp;Ephedra distachya Linn. (Gymnosperm).nbsp;nbsp;nbsp;nbsp;�E ^ nat. size).

serve to illustrate the possibility of confusion not merely between different genera of the same family, but even between membersnbsp;of different classes or groups. The long slender branches of thenbsp;Polygonum represented in (fig. 21) would naturally be referrednbsp;to Equisetum in the absence of the flowers (fig. 20 B), or withoutnbsp;a careful examination of the insignificant scaly leaves borne at

the nodes. The resemblance between Casuarina and Ephedra and the British species of Equisetum, or such a tropical form asnbsp;E. debile, speaks for itself

Endless examples might be quoted illustrating the absolute futility, in many cases, of relying on external features even fornbsp;the purpose of class distinction. An acquaintance with thenbsp;general habit and appearance of only the better known membersnbsp;of a family, frequently leads to serious mistakes. The specimennbsp;shown in fig. 22 is a leaf of a tropical fern Kaulfussia, a genusnbsp;now living in South-eastern Asia, and a member of one of thenbsp;most important and interesting families of the Filicinse, thenbsp;Marrattiaceas; its form is widely different from that which onenbsp;is accustomed to associate with fern fronds. It is unlikely thatnbsp;the impression of a sterile leaf of Kaulfussia would be recognisednbsp;as a portion of a fern plant.

Similarly in another exceedingly important group of plants, the Cycadaceie', the examples usually met with in botanicalnbsp;gardens are quite insufficient as standards of .comparison whennbsp;we are dealing with fossil forms. Familiarity with a fewnbsp;commoner types leads us to regard them as typical for the wholenbsp;family. In Mesozoic times cycadean plants were far morenbsp;numerous and widely distributed than at the present time, andnbsp;to adequately study the numerous fossil examples we need asnbsp;thorough an acquaintance as possible with the comparativelynbsp;small number of surviving genera and species. The less commonnbsp;and more isolated species of an existing family may often be ofnbsp;far greater importance to the palseobotauist than the common andnbsp;more typical forms. This importance of rare and little knownnbsp;types will be more fully illustrated in the chapters dealing withnbsp;the Cycadacese and other plant groups. Among Dicotyledons,nbsp;the Natural Order Proteaceae, at present characteristic ofnbsp;South Africa and Australia, and also represented in Southnbsp;America and the Pacific Islands, is of considerable interest tonbsp;the student of fossil Angiosperms. In a valuable addressnbsp;delivered before the Linnean Society^ in 1870 Bentham drewnbsp;attention to the marked � protean � character of the membersnbsp;of this family. He laid special stress on this particular divisionnbsp;of the Dicotyledons in view of certain far-reaching conclusions,nbsp;which had been based on the occurrence in different parts ofnbsp;Europe of fossil leaves supposed to be those of Proteaceous

genera\ Speaking of detached leaves, Bentham says:�� I do not know of a single one which, in outline or venation, isnbsp;exclusively characteristic of the order, or of any one of itsnbsp;genera.� Species of Grevillea, Hakea and a few other generanbsp;are more or less familiar in plant houses, but the leaf-formsnbsp;illustrated by the commoner members of the family convey nonbsp;idea of the enormous variation which is met with not only innbsp;the family as a whole, but in the different species of the samenbsp;genus. The striking diversity of leaf within the limits of anbsp;single genus will be dealt with more fully in volume ii. undernbsp;the head of Fossil Dicotyledons.

There is a common source of danger in attempting to carry too far the venation characters as tests of affinity. The parallelnbsp;venation of Monocotyledons is by no means a safe guide tonbsp;follow in all cases as a distinguishing feature of this class ofnbsp;plants. In addition to such leaves as those of the Gymnospermnbsp;Cordaites and detached pinnae of Cycads, there are certainnbsp;species of Dicotyledons which correspond in the character ofnbsp;their venation to Monocotyledonous leaves. Eryngium m.on-tanum Coult., E. Lassauxi Dene., and other species of thisnbsp;genus of Umbelliferee agree closely with such a plant asnbsp;Pandanus or other Monocotyledons; similarly the long linearnbsp;leaves of Richea dracophylla, R. Br., one of the Ericaceae, arenbsp;identical in form with many monocotyledonous leaves. Instances might also be quoted of monocotyledonous leaves, suchnbsp;as species of Sniilax and others which Bindley included in hisnbsp;family of Dictyogens which correspond closely with some typesnbsp;of Dicotyledons^. Venation characters must be used with carenbsp;even in determining classes or groups, and with still greaternbsp;reserve if relied on as family or generic tests.

It is too frequently the case that while we are conversant with the most detailed histological structure of a fossil plantnbsp;stem, its external form is a matter of conjecture. The conditionsnbsp;which have favoured the petrifaction of plant tissues have as anbsp;rule not been favourable for the preservation of good casts ornbsp;impressions of the external features; and, on the other hand,nbsp;in the best impressions of fern fronds or other plants, in whichnbsp;^ See also Bunbury (83) p. 309.nbsp;nbsp;nbsp;nbsp;^ Seward (96) p. 208.

the finest veins are clearly marked, there is no trace of internal structure. It is, however, frequently the case that a knowledgenbsp;of the internal structure of a particular plant enables us tonbsp;interpret certain features in a structureless cast which couldnbsp;not be understood without the help of histological facts. Anbsp;particularly interesting example of anatomical knowledgenbsp;affording a key to apparently abnormal peculiarities in anbsp;specimen preserved by incrustation, is afforded by the fructification of the genus Sphenophyllum. Some few years agonbsp;Williamson described in detail the structure of a fossil strobilusnbsp;(i.e. cone) from the Coal-Measures, but owing to the isolatednbsp;occurrence of the specimens he was unable to determine thenbsp;plant to which the strobilus belonged. On re-examining somenbsp;strobili of Sphenophyllum, preserved by incrustation, in thenbsp;light of Williamson�s descriptions, Zeiller was able to explainnbsp;certain features in his specimens which had hitherto been anbsp;puzzle, and he demonstrated that Williamson�s cone was that ofnbsp;a Sphenophyllum. Similar examples might be quoted, butnbsp;enough has been said to emphasize the importance of dealingnbsp;as far as possible with both petrifactions and incrustations.nbsp;The facts derived from a study of a plant in one form of preservation may enable us to interpret or to amplify the datanbsp;afforded by specimens preserved in another form.

The fact that plants usually occur in detached fragments, and that they have often been sorted by water, and that portionsnbsp;of the same plant have been embedded in sediment considerablenbsp;distances apart,is a constant source of difficulty. Deciduous leaves,nbsp;cones, or angiospermous flowers, and other portions of a plantnbsp;which become naturally separated from the parent tree, are metnbsp;with as detached specimens, and it is comparatively seldom thatnbsp;we have the necessary data for reuniting the isolated members.nbsp;As the result of the partial decay and separation of portions ofnbsp;the same stem or branch, the wood and bark may be separatelynbsp;preserved. Darwin^ describes how the bark often falls fromnbsp;Eucalyptus trees, and hangs in long shreds, which swing aboutnbsp;in the wind, and give to the woods a desolate and untidynbsp;appearance. In the passage already quoted from the narrativenbsp;1 Darwin, (90) p. 416.

of the voyage of the Challenger, illustrations are afforded of the manner in which detached portions of plants are likely to benbsp;preserved in a fossil state. The epidermal layer of a leaf or thenbsp;surface tissues of a twig may be detached from the underlyingnbsp;tissues and separately preserved! It is exceedingly commonnbsp;for a stem to be partially decorticated before preservation, andnbsp;the appearance presented by a cast or impression of the surfacenbsp;of a woody cylinder, and by the same stem with a part or thenbsp;whole of its cortex intact is strikingly different. The latenbsp;Prof Balfour''^ draws attention to this source of error in hisnbsp;text-book of palaeobotany, and gives figures illustrating thenbsp;different appearance presented by a branch of Araucaria imbr'i-cata Pav. when seen with its bark intact and more or lessnbsp;decorticated. Specimens that are now recognised as casts ofnbsp;stems from which the cortex had been more or less completelynbsp;removed before preservation, were originally described undernbsp;distinct generic names, such as Bergeria, Knorria and others.nbsp;These are now known to be imperfect examples of Sigillarian ornbsp;Lepidodendroid plants. Grand�Eury^ quotes the bark of Lepi-dodendron Veltheimianum Presl. as a fossil which has beennbsp;described under twenty-eight specific names, and placed innbsp;several genera.

Since the microscopical examination of fossil plant-anatomy was rendered possible, a more correct interpretation of decorticated and incomplete specimens has been considerably facilitated.nbsp;The examination of tangential sections taken at different levelsnbsp;in the cortex of such a plant as Lepidodendron brings out thenbsp;distribution of thin and thick-walled tissue. Regularly placednbsp;prominences on such a stem as the Knorria shown in fig. 23 arenbsp;due to the existence in the original stem of spirally disposednbsp;areas of thin-walled and less resistant tissue; as decay proceeded, the thinner cells would be the first to disappear, andnbsp;depressions would thus be formed in the surrounding thickernbsp;walled and stronger tissue. If the stem became embedded innbsp;mud or sand before the more resistant tissue had time to decay,nbsp;but after the removal of the thin-walled cells, the

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sediment would fill up the depressions and finally, after the complete decay of the stem, the impression on the mould or on

the cast, formed by the filling up of the space left by the stem, would have the form of regularly disposed projections markingnbsp;the position of the more delicate tissues. The specimennbsp;represented in the figure is an exceedingly interesting andnbsp;well preserved example of a Coal-Measure stem combining innbsp;itself representatives of what were formerly spoken of as distinctnbsp;genera.

The surface of the fossil as seen at e affords a typical example of the Knorria type of stem; the spirally disposednbsp;peg-like projections are the casts of cavities formed by the

decay of the delicate cells surrounding each leaf-trace bundle on its way through the cortex of the stem. The surface g exhibitsnbsp;a somewhat different appearance, owing to the fact that wenbsp;have the cast of the stem taken at a slightly different level.nbsp;The surface of the thick layer of coal at a shows very clearlynbsp;the outlines of the leaf-cushions; on the somewhat deepernbsp;surfaces b, c and d the leaf-cushions are but faintly indicated,nbsp;and the long narrow lines on the coal at c represent the leaf-traces in the immediate neighbourhood ot the leaf-cushions.

It is not uncommon among the older plant-bearing rocks to find a piece of sandstone or shale of which the surface exhibitsnbsp;a somewhat irregular reticulate pattern, the long and ovalnbsp;meshes having the form of slightly raised bosses. The size ofnbsp;such a reticulum may vary from one in which the pattern isnbsp;barely visible to the unaided eye to one with meshes more than annbsp;inch in length. The generic name Lyginodendrord was proposednbsp;several years ago (1843) for a specimen having such a patternnbsp;on its surface, but without any clue having been found as to thenbsp;meaning of the elongated raised areas separated from one anothernbsp;by a narrow groove. At a later date Williamson investigatednbsp;the anatomy of some petrified fragments of a Carboniferousnbsp;plant which suggested a possible explanation of the surfacenbsp;features in the structureless specimens. The name Lyginoden-dron was applied to this newly discovered plant, of which onenbsp;characteristic was found to be the occurrence of a hypodermalnbsp;band of strong thick-walled tissue arranged in the form of anbsp;network with the meshes occupied by thin-walled parenchyma.nbsp;If such a stem were undergoing gradual decay, the morenbsp;delicate tissue of the meshes would be destroyed first and thenbsp;harder framework left. A cast of such a partially decayednbsp;stem would take the form, therefore, of projecting areas,nbsp;corresponding to the hollowed out areas of decayed tissue, andnbsp;intervening depressions corresponding to the projecting framework of the more resistant fibrous tissue. A precisely similarnbsp;arrangement of hypodermal strengthening tissue occurs innbsp;various Palaeozoic and other plants, and casts presenting a

corresponding appearance cannot be referred with certainty to one special genus; such casts are of no real scientific valued

The old generic terms Artisia and Sternbergia illustrate another source of error which can be avoided only by meansnbsp;of a knowledge of internal structure. The former name wasnbsp;proposed by Sternberg and the latter by Artis for preciselynbsp;similar Carboniferous fossils, having the form of cylindricalnbsp;bodies marked by numerous transverse annular ridges andnbsp;grooves. These fossils are now known to be casts of thenbsp;large discoid pith of the genus Gordaites, an extinct type ofnbsp;Palaeozoic Gymnosperms. Calamites and Tylodendron affordnbsp;other instances of plants in which the supposed surfacenbsp;characters have been shown to be those of the pith-cast. Thenbsp;former genus is described at length in a later chapter, but thenbsp;latter may be briefly referred to. A cast, apparently of a stem,nbsp;from the Permian rocks of Russia was figured in 1870 under thenbsp;name Tylodendron; the surface being characterised by spirallynbsp;arranged lozenge-shaped projections, described as leaf-scars.nbsp;Specimens were eventually discovered in which the supposednbsp;stem was shown to be a cast of the large pith of a plantnbsp;possessing secondary wood very like that of the recent genusnbsp;Araucaria. The projecting portions, instead of being leaf-cushions, were found to be the casts of depressions in the innernbsp;face of the wood where strands of vascular tissue bent outwardsnbsp;on their way to the leaves. If a cast is made of thenbsp;comparatively large pith of Araucaria imhricata the featuresnbsp;of Tylodendron are fairly closely reproduced^.

A dried Bracken frond lying on the ground in the Autumn presents a very different appearance as regards the form of thenbsp;ultimate segments of the frond to that of a freshly cut leaf. Innbsp;the former the edges of the pinnules are strongly recurved, andnbsp;their shape is considerably altered. Immersed in water for somenbsp;time fern fronds or other leaves undergo maceration, and thenbsp;more delicate lamina of the leaf rots away much more rapidlynbsp;than the scaffolding of veins. Among fossil fern fronds

A good example is figured fiy Newberry (88) PI. xxv. as a decorticated coniferous stem of Triassio age.

differences in the form of the pinnules and in the shape and extent of the lamina, to which a specific value is assigned, arenbsp;no doubt in many cases merely the expression either ofnbsp;differences in the state of the leaves at the time of fossilisationnbsp;or of the different conditions under which they became embedded. Differential decay and disorganisation of plant tissuesnbsp;are factors of considerable importance with regard to the fossilisation of plants. As Lindley� and later writers have suggested,nbsp;the absence or comparative scarcity of certain forms of plantsnbsp;from a particular fossil flora may in some cases be due to theirnbsp;rapid decay and non-preservation as fossils ; it does not necessarily mean that such plants were unrepresented in thenbsp;vegetation of that period. The decayed rhizomes of thenbsp;Bracken fern often seen hanging from the roadside banksnbsp;on a heath or moorland, and consisting of flat dark colourednbsp;bands of resistant sclerenchyma in a loose sheath of the hardnbsp;shrivelled tissue, are in striking contrast to the perfect stem.nbsp;A rotting Palm stem is gradually reduced to a loose stringynbsp;mass consisting of vascular strands of which the connectingnbsp;parenchymatous tissue has been entirely removed. It mu.stnbsp;frequently have happened that detached vascular bundles ornbsp;strands and plates of hard strengthening tissue have been preserved as fossils and mistaken for complete portions of plants.

Apart from the necessity of keeping in view the possible differences in form due to the state of the plant fragments atnbsp;the time of preservation, and the marked contrast between thenbsp;same species preserved in different kinds of rock, there arenbsp;numerous sources of error which belong to an entirely differentnbsp;category. The so-called moss-agates and the well-knownnbsp;dendritic markings of black oxide of manganese, are amongnbsp;the better known instances of purely inorganic structuresnbsp;simulating plant forms.

An interesting example of this striking similarity between a purely mineral deposit and the external form of a plant isnbsp;afforded by some specimens originally described as impressionsnbsp;of the oldest known fern. The frontispiece to a well-knownnbsp;work on fossil plants, Le monde des plantes avant I�apparition de

I�homme'^, represents a fern-like fossil on the surface of a piece of Silurian slate. The supposed plant was named Eopterisnbsp;Morierei Sap., and it is occasionally referred to as the oldestnbsp;land plant in books of comparatively recent date. In thenbsp;Museum of the School of Mines, Berlin, there are some specimensnbsp;of Angers slate on some of which the cleavage face shows anbsp;shallow longitudinal groove bearing on either side somewhatnbsp;irregularly oblong and oval appendages of which the surface isnbsp;traversed by fine vein-like markings. A careful examinationnbsp;of the slate reveals the fact that these apparent fern pinnulesnbsp;are merely films of iron pyrites deposited from a solution whichnbsp;was introduced along the rachis-like channel. Many of thenbsp;extraordinary structures described as plants by Reiiisch'^ in hisnbsp;Memoir on the minute structure of coal have been shown to benbsp;of purely mineral origin.

The innumerable casts of animal-burrows and trails as well as the casts of egg-cases and various other bodies, which havenbsp;been described as fossil algae, must be included among the mostnbsp;fruitful sources of error.

It requires but a short experience of microscopical investigation of fossil plant structures to discover numerous pitfalls in the appearance presented by sections of calcareousnbsp;and siliceous nodules. The juxtaposition of tissues apparentlynbsp;parts of the same plant, and the penetration by growing rootsnbsp;of partially decayed plant d�bris, serve to mislead an unpractisednbsp;observer. In sections of the English � calcareous nodules �nbsp;one very frequently finds the tissue of Stigmarian appendagesnbsp;occupying every conceivable position, and preserved in placesnbsp;admirably calculated to lead to false interpretations. The morenbsp;minute investigation of tissues is often rendered difficult bynbsp;deceptive appearances simulating original structures, but whichnbsp;are in reality the result of mineralisation. It is no easy matternbsp;in some cases to discover whether a particular cell in a fossilnbsp;tissue was originally thick-walled, or whether its sclerous

1 nbsp;nbsp;nbsp;Saporta (79) (77). Eopteris is included among the ferns in Schimper andnbsp;Schenk�s volume of Zittel�s Handbuch der Palaeontologie (p. 115), and in somenbsp;other modern works.

appearance is due to the deposition of mineral matter on the inside of the thin cell-membrane. Examples of such sourcesnbsp;of error as have been briefly referred to, and others, will benbsp;found in various parts of the descriptive portions of this book.

There is one other form of pitfall which should be briefly noticed. In sections of petrified plants one occasionally findsnbsp;clean cut canals penetrating a mass of tissue, and differing in

their manner of occurrence and in their somewhat larger size from ordinary secretory ducts. Such tunnels or canals arenbsp;probably the work of a wood-boring animal. An example isnbsp;illustrated in fig. 24 A. Similarly it is not unusual to meet withnbsp;groups or nests of spherical or elliptical bodies lying amongnbsp;plant tissues, and having the appearance of spores. Such

spore-like bodies appear on close examination to be made up of finely comminuted particles of tissue, and in all probabilitynbsp;they are the coprolites of some xylophagous animal. Examplesnbsp;of such coprolites are shown in fig. 24 A and in fig. 24 jBnbsp;an interesting manner of occurrence of these misleading bodiesnbsp;is represented. The framework of cells enclosing the nest ofnbsp;coprolites in fig. 24 �, represents the outer tissues of a Lepi-dodendroid or a Sigillarian leaf; the inner tissues have beennbsp;destroyed and the cavity is now occupied by what may possiblynbsp;be the excreta of the wood-eating animal.

Some of the oval spore-like structures met with in plant tissues may, as Renault has suggested, be the eggs of annbsp;Arthropod In a section of a calcareous Coal-Measure nodule innbsp;the Williamson collection (British Museum)* there occur severalnbsp;fungal spores or possibly oogonia lying among imperfectlynbsp;preserved Stigmarian appendages. Associated with these arenbsp;numerous dark coloured and larger bodies consisting of a cavitynbsp;bounded by a simple membrane; the larger bodies may well benbsp;the eggs of some Arthropod or other animal.

In looking through the collections of Coal-Measure plants in the Museums of Berlin, Vienna and other continental towns,nbsp;one cannot fail to be struck with the larger size of many of thenbsp;specimens as compared with those usually seen in Englishnbsp;Museums. The facilities afforded in the State Collieries ofnbsp;Germany to the scientific investigator may account in partnbsp;at least for the better specimens which he is able to obtain.nbsp;It would no doubt be a great gain to our collections of Coal-Measui�e plants if arrangements could be made in some collieriesnbsp;for the preservation of the finer specimens met with in the working of the seams, instead of breaking up the slabs of shale andnbsp;consigning everything to the waste heaps. There is one morenbsp;point which should be alluded to in connection with possiblenbsp;sources of error, and that is the essential importance of accuracy in the illustration of specimens, especially as regard

1 Williamson has drawn attention to the occurrence of such borings and coprolites in Coal-Measure plant tissues. JH-g. Williamson (80) PI. 20, figs. 65nbsp;and 66.

type-specimens. It is often impossible to inspect the original fossils -which have served as types, and it is of the utmostnbsp;importance that the published figures should he as faithful asnbsp;possible. M. Crepin^ of Brussels, in an article on the use ofnbsp;photography in illustrating, has given some examples of thenbsp;confusion and mistakes caused by imperfect dra-wings. It doesnbsp;not require a long experience of palaeobotanical -work to demonstrate the need of care in the execution of dra-wings for reproduction.

CHAPTER VI.

� I do not think more credit is due to a man for defining a species, than to a carpenter for making a box.�

Any attempt to discuss at length the difficult and thorny question of nomenclature would be entirely out of place in annbsp;elementary book on fossil plants, but there are certain importantnbsp;points to which it may be well to draw attention. When anbsp;student enters the field of independent research, he is usuallynbsp;hut imperfectly acquainted with the principles of nomenclaturenbsp;which should be followed in palaeontological work. Afternbsp;losing himself in a maze of endless synonyms and confusednbsp;terminology, he recognises the desirability of adopting somenbsp;definite and consistent plan in his method of naming genera andnbsp;species. It is extremely probable that whatever system is madenbsp;use of, it will be called in question by some critics as not beingnbsp;in strict conformity with accepted rules. The opportunities fornbsp;criticism in matters relating to nomenclature are particularlynbsp;numerous, and the critic who may be but imperfectlynbsp;familiar with the subject-matter of a scientific work is notnbsp;slow to avail himself of some supposed eccentricity on the partnbsp;of the author in the manner of terminology. The true value ofnbsp;work may be obscured by laying too much emphasis on thenbsp;imperfections of a somewhat heterodox nomenclature. On thenbsp;other hand good systematic work is often seriously spoilt bynbsp;a want of attention to generally accepted rules in namingnbsp;and defining species. It is essential that those who take up

systematic research should pay attention to the necessary though secondary question of technical description.

In inventing a new generic or specific name, it is well to adhere to some definite plan as regards the form or termination ^nbsp;of the words used. To deal with this subject in detail, or tonbsp;recapitulate a series of rules as to the best method of constructing names whether descriptive or personal, would takenbsp;us beyond the limits of a single chapter. The student shouldnbsp;refer for guidance to such recognised rules as those drawn upnbsp;by the late Mr Strickland and others at the instance of thenbsp;British Association h

It is not infrequently the case that the same generic name has been applied to a fossil and to a recent species. Such anbsp;double use of the same term should always be avoided as likelynbsp;to lead to confusion, and as tending to admit a divorce betweennbsp;botany and palaeobotany.

In the course of describing a collection of fossil species, various problems are bound to present themselves as regardsnbsp;the best method of dealing with certain generic or specificnbsp;names. A few general suggestions may prove of use to �nbsp;those who are likely to be confronted with the intricacies ofnbsp;scientific and pseudoscientific terminology.

In writing the name of a species, it is important to append the name, often in an abbreviated form, of the author who firstnbsp;proposed the accepted specific designation. Stigmaria ficoidesnbsp;Brongn. written in this form records the fact that Brongniartnbsp;was the author of the specific name ficoides. It means, moreover, that Brongniart not only suggested the name, but that henbsp;was the first to give either a figure or a diagnosis of this particularnbsp;fossil. It is frequently the case that a specific name is proposednbsp;for a new species, without either figures or description ; suchnbsp;a name is usually regarded as a nomen nudum, and must yieldnbsp;priority to the name which was first accompanied by somenbsp;description or illustration sufficiently accurate to afford a meansnbsp;of recognition. A practice which may be recommended on thenbsp;score of convenience is to write the name of the author of a

^ Rules for Zoological Nomenclature, drawn up by the late H. E. Strickland, M.A., F.E.S., London, 1878.

species in brackets if he was not the first to use the generic as well as the specific name. Onychiopsis Mantelli (Brongn.) tellsnbsp;us that Brongniart founded the species, but made use of somenbsp;other generic name than that which is now accepted. Thisnbsp;leads us to another point of some importance. Brongniartnbsp;described this characteristic Wealden fern under the namenbsp;Sphenopteris Mantelli', Sphenopteris being one of those extremely useful provisional generic terms which are usednbsp;in cases where we have no satisfactory proof of precisenbsp;botanical affinity. Sphenopteris stands for fern fronds havingnbsp;a certain,habit, form of segment and venation, and in this widenbsp;sense it necessarily includes representatives of various divisionsnbsp;and genera of Filices. If an example of a sphenopteroid frondnbsp;is discovered with sori or spores sufficiently well preserved tonbsp;enable us to determine its botanical position within narrowernbsp;limits, we may with advantage employ another genus in placenbsp;of the purely artificial form-genus which was originally chosennbsp;as a consequence of imperfect knowledge. Fronds of thisnbsp;Wealden fern have recently been found with well defined fertilenbsp;segments having a form appgj-ently identical with that whichnbsp;characterises the polypodiaceous genus Onychium. For thisnbsp;reason the name Onychiopsis has been adopted. It is safer andnbsp;more convenient to use a name which differs in its terminationnbsp;from that of the recent plant with which we believe the fossilnbsp;to be closely related. A common custom is to slightly alter thenbsp;recent name by adding the termination -opsis or -ites. Therenbsp;are several other provisional generic terms that are often usednbsp;in Fossil Botany, and which might be advantageously chosennbsp;in many cases where the misleading resemblance of externalnbsp;form has often given rise to the use of a name implyingnbsp;affinities which cannot be satisfactorily demonstrated.

It was the custom of some of the earliest writers, in spite of their habit of using the names of recent I'lowering plants fornbsp;extinct Palaeozoic species of Vascular Cryptogams, to adoptnbsp;also general and comprehensive terms. We find such a namenbsp;as Lithoxylon employed by Lhwyd^ in 1699 as a convenientnbsp;designation for fossil wood.

One of the most important and frequently disputed questions associated with the naming of species is that of priority. Nonbsp;name given to a plant in pre-Linnaean days need be considered,nbsp;as our present system of nomenclature dates from the institutionnbsp;of the binominal system by Linnaeus. As a general rule, whichnbsp;it is advisable to follow, the specific name which was first givennbsp;to a plant, if accompanied by a figure or diagnosis, should takenbsp;priority over a name of later date. If A in 1850 describes anbsp;species under a certain name, and in 1860 � proposes a newnbsp;name for the same species, either in ignorance of the oldernbsp;name or from disapproval of A�s choice of a specific term, thenbsp;later name should not be allowed to supersede A�s originalnbsp;designation. Such a rule is not only just to the originalnbsp;author, but is one which, if generally observed, would lead tonbsp;less confusion and would diminish unnecessary multiplication ofnbsp;specific names. Some writers would have us conform in allnbsp;cases to this rule of priority, which they consistently adherenbsp;to apart from all considerations of convenience or long-established custom. There are, however, cogent reasons for maintaining a certain amount of freedom. While accepting prioritynbsp;as a good rule in most cases, it is unwise to allow ourselves to benbsp;too servile in our conformity to a principle which was framed innbsp;the interests of convenience, if the strict application of the rule .nbsp;clearly makes for confusion and inconvenience. A name maynbsp;have been in use for say eighty years, and has become perfectlynbsp;familiar as the recognised designation of a particular fossil; it isnbsp;discovered, however, that an older name was proposed for thenbsp;same species ninety years ago, and therefore according to thenbsp;priority rule, we must accustom ourselves to a new name innbsp;place of one which is thoroughly established by long usage.nbsp;From a scientific point of view, the ideal of nomenclature is tonbsp;he plain and intelligible. To prefer priority to established usagenbsp;entails obscurity and confusion. If priority is to be the rulenbsp;which we must invariably obey in the shadowy hope that bynbsp;such means finality in nomenclature^ may be reached, it becomesnbsp;necessary for the student to devote no inconsiderable portion

of his time to antiquarian research, with a view to discover whether a particular name may be stamped with the hallmark of �the very first.� While admitting the advisability ofnbsp;retaining as a general principle the original generic or specificnbsp;name, the extreme subservience to � the priority craze � withoutnbsp;regard to convenience, would seem to lead irresistibly to thenbsp;view that �botanists who waste their time over priority arenbsp;like boys who, when sent on an errand, spend their time innbsp;playing by the roadside

There is another point which cannot be satisfactorily settled in all cases by a rigid adherence to an arbitrary rule. How farnbsp;should we regard a generic name in the sense of a mere marknbsp;or sign to denote a particular plant, or to what extent may wenbsp;accept the literal meaning of the generic term as an index ofnbsp;the affinity or character of the plant ? If we consider thenbsp;etymology of many generic names, we soon find that they arenbsp;entirely inappropriate as aids in recognizing the true taxonomicnbsp;position of the plants to which they are applied. The genericnbsp;name Calamites was first suggested by the supposed resemblance of this Palaeozoic plant to recent reeds. If considerednbsp;etymologically, it is merely a record of a past mistake, but itnbsp;would be absurd to discard such a well-known name on thenbsp;grounds that the genus is a Vascular Cryptogam and farnbsp;removed from reeds. On the other hand, there often arisenbsp;cases which present a real difficulty. The following examplenbsp;conveniently illustrates two distinct points of view as regardsnbsp;generic nomenclature. In 1875 Saporta described and figurednbsp;a fragment of a fossil plant from the Jurassic beds of France asnbsp;Cycadorachis armata'^; the name being chosen in the belief thatnbsp;the specimen was part of a cycadean petiole, and there werenbsp;good grounds for such a view. A few years ago Mr Ruffordnbsp;discovered more perfect specimens, in the Wealden rocks ofnbsp;Sussex, clearly belonging to Saporta�s genus, and these affordednbsp;definite evidence that Saporta had been deceived by thenbsp;imperfection of the specimens as to their true botanicalnbsp;position. Owing to the obviously misleading name first given

to this plant, I ventured to substitute Withamia'^ for Gycado-rachis,. and chose such a term in preference to one denoting affinity, on account of the difficulty of placing the plant in anbsp;definite class or family. On the other hand, it has beennbsp;objected that the original name, despite its meaninglessnbsp;meaning�if the expression may be used�should be retained.nbsp;A friendly criticquot;, in writing of the proposed change of Cycado-rackis, urges the importance of adhering to the name whichnbsp;was first applied to a genus. The same author pertinentlynbsp;remarks that we can no more dispense with a nomenclaturenbsp;than we can dispense with language. We may extend thenbsp;comparison and point out that in language, as in scientificnbsp;nomenclature, conciseness, clearness and convenience should benbsp;kept in view as guiding principles.

The student must judge for himself what course to follow in each case. While adhering as far as possible to a consistentnbsp;plan, he must take care that he does not allow his ownnbsp;judgment to be completely over-ridden by a blind obediencenbsp;to fixed rules, which if pressed too far may defeat their ownnbsp;ends.

PAET II. SYSTEMATIC.

CHAPTER VIT.

The divisions of the plant kingdom dealt with in the following chapters of Volume l. are taken in their naturalnbsp;sequence, beginning with the lowest and passing gradually tonbsp;the highest groups. The list of the classes and familiesnbsp;included in Chapters VII.�XI. is given in the table ofnbsp;contents preceding Chapter I.

Thallophytes are of the simplest type, but they exhibit a very wide range as regards both the structure and differentiationnbsp;of the vegetative body and the methods of reproduction. Innbsp;some cases the individual consists of a minute simple cell whichnbsp;multiplies by cell-division; in others the body or thallus isnbsp;made up of a number of similar units, while in a greatnbsp;number of forms there is a well-marked physiological divisionnbsp;of labour, as expressed both in the external division of thenbsp;thallus into distinct organs corresponding in function to the root,nbsp;stem, and leaves of the higher plants, and further in the highnbsp;degree of histological differentiation of the tissues. In othernbsp;thallophytes, again, the thallus is a coenocyte either unseptatenbsp;or incompletely septate; that is, the individual consists of anbsp;single cell differing from a true plant-cell, in the stricter sensenbsp;of the term, in possessing several nuclei, in other words, thenbsp;thallus is divided up into compartments by transverse septa,nbsp;but each division contains more than one nucleus. Such

coenocytic plants may show well-marked external differentiation of the thallus into members or parts subserving different functions.

A similar wide range is covered by the methods of reproduction among thallophytes.

The organisms included under this head are of little importance from a palaeontological point of view, but a briefnbsp;reference may be made to them as a section of the Thallophyta.

The Peridiniales include very small single-celled organisms which have often been described as occupying a position on thenbsp;borderland between animals and plants, lying on the � shadowynbsp;boundarj^ between animal and vegetable life.� The individualsnbsp;are rarely naked, more frequently they are covered with a cellulose or mucilaginous investment which has frequently the formnbsp;of two or more minute armour-like plates of a limiting membrane. The chromatophores are green, yellow, brown ornbsp;colourless. Simple division is the usual method of reproduc-tion, but spores have been described as occurring in somenbsp;species. The motile forms are provided with cilia. Thenbsp;Peridiniaceae, a section of the Peridiniales, are regarded asnbsp;nearly related to the Diatoms.

The Peridiniales play an important role in the Plankton flora of the sea and freshwater lakes, and have a world-widenbsp;distribution. In the narrative of the Challenger cruise theynbsp;are described as occasionally filling the tow-nets with a yellownbsp;coloured slime h Some genera, such as Ceratium, are found innbsp;enormous numbers off the British coast.

As an example of the occurrence of fossil representatives of the Peridiniaceae reference may be made to one of two speciesnbsp;of Peridmium described by Ehrenberg in 1836. These werenbsp;found in a siliceous rock described as Cretaceous in age fromnbsp;Delitszch in Saxony. A comparison of Ehrenberg�s figures ofnbsp;the fossil species Peridinium pyrophorum, Ehrenb.'^ with thosenbsp;1 Challenger (85) p. 934.

- Ehrenberg (36) p. 117, Pl. i. figs. 1 and 4, and Ehrenberg (54) PI. XXXVII. fig. vii.

of the recent species Peridinium divergens Ehrenb., as given Schiitt' and other writers, brings out clearly the very closenbsp;resemblance if not identity of the two forms. Butschli^ innbsp;his account of the Dinoflagellata in Bronn�s Thier-Bsiclinbsp;confirms Ehrenberg�s determination of Peridinium pyrophorum,nbsp;and points out its striking agreement with the recent species.

Our knowledge of these minute calcareous organisms is derived from Huxley�s description of coccoliths from thenbsp;Atlantic in 1857, and from the accounts of Wallich, Johnnbsp;Murray, and other writers. In the first volume of the narrativenbsp;of the Challenger cruise � and in the volume on deep-seanbsp;deposits^ these minute forms of life are figured and described.nbsp;In the latter volume both genera are spoken of as extremelynbsp;abundant in the surface waters of the tropical and temperate regions of the open ocean, and as forming an important constituentnbsp;of the Globigerine ooze; they are said to occur entangled in thenbsp;arelatinous substance of the Badiolarians, Diatoms, and Forami-nifera, and are very common in the stomachs of Salps, Pteropodsnbsp;and other pelagic animals. Rhabdospheres are rare in regionsnbsp;where the temperature of the water sinks below 65� F.; thenbsp;Coccospheres occur in tropical and ternperate latitudes, andnbsp;extend further north and south than the Rhabdospheres. Asnbsp;regards their botanical position, John Murray expresses thenbsp;view that they are in all probability pelagic algae.

In the interesting memoir by Schiitt on the Pjianzenlehen der Hochsee^ there occurs a short reference to the forms described in the Challenger Reports, but they were not obtainednbsp;by the staff' of the,Hensen Plankton Expedition and Schtitt�snbsp;remarks are not based therefore on personal observations.nbsp;While admitting the existence of such bodies, he points outnbsp;that Zoologists have referred Coccospheres and Rhabdospheres

to the algae as organisms which cannot be included in any group of animals, and Sch�tt is unable to recognise a sufficient reasonnbsp;for referring them to this class of plants. It is suggested indeednbsp;that they may be purely inorganic structures.

The most recent account of these two genera is by Messrs G. Murray and Blackman in a short notice in Nature for April 1,nbsp;1897'. Numerous examples of Coccospheres and Rhabdospheresnbsp;were obtained by Capt. Milner of the R.M.S. Para during anbsp;voyage to Barbados by allowing the sea water to enter the feedpipe of the boiler through a fine muslin net. All the formsnbsp;described in the Challenger Reports were met with, and annbsp;examination of the material by means of extremely high

Cocoosphere x 1300. B, Rhabdosphere x 900. G, Portion of tbe same x 1300. D, Rhabdosphere of another type, in optical sectionnbsp;X 1900. E, Tbe same in surface view x 1900. F, End of one of thenbsp;trumpet-shaped appendages of E.

objectives has confirmed the original account of the genera, and added some points to our previous knowledge.

Coccospheres (fig. 25 A). Spherical bodies of exceedingly small size, consisting of a central protoplasmic vesicle covered withnbsp;overlapping circular calcareous scales, each of which is attachednbsp;to the minute cell by a button-like projection. The scalesnbsp;are frequently found detached and are then spoken of asnbsp;Coccoliths.

Rhabdospheres (fig. 25 B�F). Spherical bodies, extremely minute, consisting of a single cell, on the surface of which arenbsp;embedded numerous calcareous plates bearing long blunt spinesnbsp;(fig. 25, G) or beautiful trumpet-like appendages (fig. 25, D�F).nbsp;The detached plates of Rhabdospheres are known as Rhabdoliths.

In addition to the text-figures of Coccospheres and Rhabdospheres in the Challenger Reports, the same structuresnbsp;are shown in samples of globigerine ooze figured in Plate XI.nbsp;of the Monograph on deep-sea deposits. In a recent number ofnbsp;Nature Messrs Dixon and Joly^ have announced the discoverynbsp;of Coccoliths and Coccospheres in the coastal waters off Southnbsp;County Dublin. They estimate that in one sample of waternbsp;taken about three miles from the Irish coast there were 200nbsp;Coccoliths in each cubic centimetre of sea water.

The interest of these calcareous bodies from a palaeobotani-cal point of view lies in the fact that similar forms have been recognized in the Chalk and the Upper Lias. Sorby, in hisnbsp;memorable Address delivered before the Geological Society innbsp;1879, refers to the abundance of Coccoliths in sections of chalknbsp;which he examined^ Rothpletz� has recently recorded thenbsp;occurrence of numerous Coccoliths, 5�12 in diameter, associated with the skeleton of a horny sponge (Phymatoderma) ofnbsp;Liassic age.

The question of the nature of Coccospheres and Rhabdospheres cannot be regarded as definitely settled. It has been shown by J. Murray, and more recently by G. Murraynbsp;and V. H. Blackman, that on the solution of the calcareousnbsp;material by a weak acid there remains a small gelatinous body

apparently protoplasmic in nature. We may at least express the opinion that Schiitt�s suggestion as to their being inorganic mustnbsp;be ruled out of court. It would appear that they are extremelynbsp;minute unicellular organisms characterised by a delicate calcareous armour consisting of numerous plates or scales. Wenbsp;know nothing as to their life-history, and cannot attempt tonbsp;determine their affinities with any degree of certainty untilnbsp;further facts are before us. It is not improbable that they arenbsp;algae of an extremely minute size, and the evidence so farnbsp;obtained would lead us to regard them as complete individualsnbsp;rather than the reproductive cells of some larger organism.nbsp;Mr George Murray is of opinion that they are certainly algae,nbsp;but he considers that they cannot be included in any existingnbsp;family. It is conceivable that they may be minute eggs ornbsp;reproductive cells of animals or plants, but on the whole thenbsp;balance of probability would seem to be in favour of regardingnbsp;them as autonomous organisms.

In this group are included small single-celled plants of an extremely low type of organisation, in which reproduction takesnbsp;the form of multiplication by simple cell-division, or thenbsp;formation of spores. The characteristic method of reproductionnbsp;by division has given rise to the general term Fission-plants fornbsp;this lowest sub-class in the vegetable kingdom. In-many casesnbsp;the members of this sub-class contain chlorophyll, and associatednbsp;with it a blue-green colouring matter; such plants are classednbsp;together as the Blue-green algae, Cyanophyceae, or Schizophy-'nbsp;ceae. Others, again, are destitute of chlorophyll, and may benbsp;conveniently designated Schizomycetes or Fission-fungi. Seeingnbsp;how close is the resemblance and relationship between thenbsp;members of the sub-class, it has been the custom to includenbsp;them as two parallel series under the general head, Schizophyta,nbsp;rather than to incorporate them among the Algae and Funginbsp;respectively.

Chroococcaceae. Thallus of a single cell, the cells may be either free, or more usually joined together in colonies envelopednbsp;by a common gelatinous matrix, formed by the mucilaginousnbsp;degeneration of the outer portion of the cell-walls. Reproduction by means of simple division or resting cells.

Nostocaceae. Thallus consists of simple or branched rows of cells in which special cells known as heterocysts often occur.nbsp;Reproduction by means of germ-plants or hormogonia, or bynbsp;resting cells specially modified to resist unfavourable conditions.

In both families the individuals are surrounded by a gelatinous envelope, which in some genera assumes the formnbsp;of a conspicuous and comparatively resistant sheath. Marine,nbsp;freshwater, and aerial forms are represented among recentnbsp;genera. Several species occur as endophytes, living in thenbsp;tissues or mucilage-containing spaces in the bodies of highernbsp;plants. In addition to the frequent occurrence of blue-greennbsp;algae in freshwater streams and on damp surfaces, certain formsnbsp;are particularly abundant in the open seah and in lakes ornbsp;meres^ where they are the cause of what is known in somenbsp;parts of the country as � the breaking of the meres � (� Fleursnbsp;d�eau �). From the narrative of the cruise of the Challenger,nbsp;we learn that the Oscillariaceae are especially abundant in thenbsp;surface waters of the ocean. The �sea sawdust� so named bynbsp;Cook�s sailors^, and the same floating scum collected by Darwinquot;*,nbsp;affords an illustration of the abundance of some of these blue-green algae in the sea.

Another manner of occurrence of these plants has been recorded by different writers, which is of special importancenbsp;from the point of view of fossil algae. On the shores of thenbsp;Great Salt Lake, Utah, there are found numerous smallnbsp;oolitic calcareous bodies thrown up by the waves�. Thesenbsp;are coated with the cells of Gloeocapsa and Gloeotheca, twonbsp;genera of the Chroococcaceae. Sections of the grains reveal

the presence of the same forms in the interior of the calcareous matrix, and it has been concluded on good evidence that thenbsp;algae are responsible for the deposition of the carbonate of limenbsp;of the oolitic grains. By extracting the carbonic acid whichnbsp;they require as a source of food, from the waters of the lake,nbsp;the solvent power of the water is decreased and carbonate ofnbsp;lime is thrown down. In similar white grains from the Rednbsp;Sea^ there is a central nucleus in the form of a grain of sand,nbsp;and cells of Chroococcaceae occur in the surrounding carbonatenbsp;of lime as in the Salt Lake oolite. Prof. Cohn of Breslau innbsp;1862 demonstrated the importance of low forms of plant life innbsp;the deposition of the Carlsbad � Sprudelstein^� On the bottomnbsp;of Lough Belvedere, near Mullingar in Ireland�, there occurnbsp;numerous spherical calcareous pebbles, of all sizes up to that ofnbsp;a filbert, From a pond in Michigan (U.S.A.)* similar bodiesnbsp;have been obtained varying in diameter from one to three andnbsp;a-half inches. In the former pebbles a species of ScMzothrix,nbsp;one of the Nostocaceae occurs in abundance, in the form ofnbsp;chains of small cells enclosed in the characteristic and comvnbsp;paratively hard tubular sheath, and associated with Schizothnxnbsp;fasciculata there have been found Nostoc cells and the siliceousnbsp;frustules of Diatoms. In the Michigan nodules the samenbsp;Schizothrix occurs, associated with Stigonema and Dichothrix,nbsp;other genera of the Nostocaceae. One of the Michigan pebblesnbsp;is shown in section in fig. 32 I).

The connection between the well-known oolitic structure, characteristic of rocks of various ages in all parts of the world,nbsp;and the presence of algal cells is of the greatest interest from anbsp;geological point of view. In recent years considerable attentionnbsp;has been paid to the structure of oolitic rocks, and in manynbsp;instances there have been found in the calcareous grainsnbsp;tubular structures suggestive of simple cylindrical plants, whichnbsp;have probably been concerned in the deposition of the carbonate of lime of which the granules consist. In 1880 Messrsnbsp;Nicholson and Etheridge� recorded the occurrence of such a

tubular structure in calcareous nodules obtained from a rock of Ordovician age in the Girvan district of Scotland. Thesenbsp;Authors considered the tubes to be those of some Rhizopod,nbsp;and proposed to designate the fossil Girvanella.

Since this diagnosis was published very many examples of similar tubular fossils have been described by several writersnbsp;in rocks from widely separated geological horizons. The accompanying sketch (Fig. 26), drawn from a micro-photographnbsp;kindly lent to me by Mr M^ethered of Cheltenham, who hasnbsp;made oolitic grains a special subject of careful investigation,nbsp;affords a good example of the occurrence of such tubularnbsp;structures in an oolitic grain of Silurian age from the Wenlock

limestone of May Hill, Gloucestershire�. In the centre is a crystalline core or nucleus round which the tubules have grown,nbsp;and presumably they had an important share in the depositionnbsp;of the calcareous substance. The nature of Girvanella, and stillnbsp;more its exact position in the organic world, is quite uncertain;nbsp;it is mentioned rather as d propos of the association ofnbsp;recent Cyanophyceae with oolitic structure, than as a well-defined genus of fossil algae.

In the desciption of the calcareous nodules from Michigan, Murray speaks of the Schizothrix filaments at the surface of thenbsp;pebbles as fairly intact, while nearer the centre only sheathsnbsp;were met with. It is conceivable that in some of the tubularnbsp;structures referred to Girvanella we have the mineralised sheathsnbsp;of a fossil Cyanophyceous genus��. The organic nature of thesenbsp;tubules has been a matter .of dispute, but we may probablynbsp;assume with safety that in some at least of the fossil ooliticnbsp;grains there are distinct traces of some simple organism whichnbsp;was in all likelihood a plant. Some authors have suggested thatnbsp;Girvanella is a calcareous alga which should be included in thenbsp;family Siphoneae^. As a matter of fact we must be content for ^nbsp;the present to leave its precise nature as still sub judice, andnbsp;while regarding it as probably an alga, we may venture tonbsp;consider it more fittingly discussed under the Schizophyta thannbsp;elsewhere.

Wethered^ would go so far as to refer oolitic structure in general to an organic origin. While admitting that anbsp;Girvanella-like structure has been very frequently met with innbsp;oolitic rocks, it would be unwise to adopt so far-reaching anbsp;conclusion. It is at least premature to refer the formation ofnbsp;all oolitic structure to algal agency, and the evidence adducednbsp;is by no means convincing in every case. The discovery ofnbsp;Girvanella and allied forms in rocks from the Cambrian�,

^ For figures of the sheaths of Cyanophyceous algae, see Murray (Oo'h, H. XIX. fig. 5. Gomont (88) and (92); etc.

Ordovician, Silmdan, Carboniferous, Jurassic and other systems is a striking fact, and lends support to the view that ooliticnbsp;structure is in many cases intimately associated with thenbsp;presence of a simple tubular organism. Among recent algaenbsp;we find different genera, and representatives of different families,nbsp;growing in such a manner and under such circumstances as arenbsp;favourable to the formation of a ball-like mass of algal threads,nbsp;which may or may not be encrusted with carbonate of lime.nbsp;Similarly as regards oolitic grains of various sizes, and thenbsp;occurrence in rocks of calcareous nodules, the tubular structurenbsp;is not always of precisely the same type, and cannot always benbsp;included under the genus Girvanella.

Several observers have recorded the occurrence of low forms of plant-life in the waters of thermal springs. It has beennbsp;already mentioned that Cohn described the occurrence ofnbsp;simple plants in the warm Carlsbad Springs, and fission-plantsnbsp;of various types have been discovered in the thermal watersnbsp;of Iceland, the Azoresh New Zealand, the Yellowstone Park,nbsp;Japan, India, and numerous other places;

A lew years ago Mr Weed, of the geological survey of the United States, published an interesting account of the formation of calcareous travertine and siliceous sinter in the Yellowstone Park districts This author emphasizes the importantnbsp;role of certain forms of plants in the building up of the calcareous and siliceous material. Among other forms of frequentnbsp;occurrence, Galothrix gypsophila and a species Leptothrix arenbsp;mentioned, the former being a member of the Nostocaceae, alliednbsp;to Rivularia, and the latter a genus of Schizomycetes. In manynbsp;of the springs there are found masses of algal jelly like thosenbsp;previously described by Cohn in the Carlsbad waters. Sectionsnbsp;of such dried jelly showed a number of interlaced filamentsnbsp;with glassy silica between them. Weed refers to the occurrence of small gritty particles in this mucilaginous material.nbsp;These are calcareous oolitic granules which are eventuallynbsp;cemented together into a compact and firm mass of travertinenbsp;by the continued deposition of carbonate of lime. The presencenbsp;of the plant filaments is often difficult to recognise in thenbsp;i Moseley, H. N. (75), p. 321.nbsp;nbsp;nbsp;nbsp;2 Weed (87-88), vide also Tilden (97).

� leathery sheet of tough gelatinous material,� or in � the skeins of delicate white filaments� which make up the travertinenbsp;deposits.

Under the head of Cyanophyceae, mention should he made of the recent genus Hyella^, which occurs as a perforating or boringnbsp;alga in the calcareous shells of molluscs. On dissolving thenbsp;carbonate of lime of shells perforated by this alga, the latter,nbsp;is isolated and appears to consist of rows of small cells, withnbsp;possibly some sporangia containing spores. Other boring algaenbsp;have been recorded among the Chlorophyceae, and recently anbsp;member of the Rhodophyceae^ has been found living in thenbsp;substance of calcareous shells. Such examples are worthy ofnbsp;note in view of the not infrequent occurrence of fossil corals,nbsp;shells and fish-scales, which have evidently been bored by annbsp;organism resembling in form and manner of occurrence thesenbsp;recent algal borers.

The occurrence of small ramifying tubes in recent and fossil corals, fish-scales, and bones was long ago pointed out bynbsp;Quekett^ K�lliker^ Rose� and other writers�. These narrownbsp;tubular cavities have generally been attributed to the boringnbsp;action of some parasitic organism, either a fungus or an alga.nbsp;In 1876 Duncan published two important papers^ dealing withnbsp;the occurrence of such tubes in recent corals, as well as innbsp;the calcareous skeleton of Calceolina, Goniopliyllum and othernbsp;Palaeozoic, Mesozoic and Tertiary species of corals. This writernbsp;attributed the formation of the cavities in the case of the fossilnbsp;species to the action of a fungus which he named Palaeachylanbsp;perforans, and considered as very nearly related to Achylanbsp;penetrans found in the � dense sclerenchyma � of recent corals.nbsp;In fig. 27 A. is reproduced one of the drawings given by Rose �

� Qiiekett (54), fig. 78. nbsp;nbsp;nbsp;^ K�lliker (59) and (59�); good figures'in the

� Similar borings are figured by K�lliker (59�), PI. xyi. 14, in a scale of Beryx ornatus from the Chalk.

in his paper published in 1855; it shows a section of a fish-scale from the Kimeridge clay which has been attacked by a boring organism. Rose attributes the dichotomously branchednbsp;canals to some � infusorial parasite.�

In the important paper by MM. Bornet and Flahault on perforating algae a full description is given of various boringnbsp;forms belonging to the Chlorophyceae and the Cyanophyceaehnbsp;The canals which these algae produce in calcareous shells andnbsp;other hard substances are of the same type as those previouslynbsp;described in fossil corals, fish-scales and bones. In dealingnbsp;with living perforating Thallophytes the colour and other cell-contents often enable us to distinguish between algae and fungi,nbsp;but in fossil specimens such tests cannot be applied. Thenbsp;fossil tubular borings may or may not show traces of the transverse septa and reproductive cells; it is often the case that nonbsp;1 Bornet and Flahault (89^).

trace of the organism has been left, but only the canals by which it penetrated the calcareous or bony skeleton. In somenbsp;of the examples of Palaeachlya figured by Duncan there appearnbsp;to be numerous spores in some of the sections, but it isnbsp;generally a very difficult and often an impossible task to discriminate between the borings of fungi and algae in fossilnbsp;material.

Fig. 27 B, which is copied from one of Bornet and Flahault�s drawings, represents a piece of Solen shell riddled with smallnbsp;canals made by the organism which has been named by thenbsp;French authors Ostracoblabe implexa, and regarded by them asnbsp;a fungus. Fig. 27 C represents a small piece of the vegetativenbsp;body of Ostracoblabe obtained from a decalcified shell. Innbsp;endeavouring to determine the organism which has producednbsp;borings in fossil corals or shells, it must be borne in mind thatnbsp;some forms of canals or passages may have been the work ofnbsp;perforating sponges, but these are larger in diameter than thosenbsp;made by algae or fungi. By some writers^ the tubular cavitiesnbsp;in shells have been referred to true algae, but others considernbsp;them to be of fungal origin.

As an example of a fossil alga referred to the Cyanophyceae, the genus Zonatrichites^ may be quoted. Bornemann, who firstnbsp;described the specimens, points out the close resemblance innbsp;habit to some members of the recent Rivulariaceae.

�A calcareous alga, with radially arranged filamente, forming hemispherical or kidney-shaped layers, growing on or enclosing other bodies. Parallel or concentric zones are seen in cross-section, formed by thenbsp;periodic growth of the alga, the older and dead layers serving as a foundation on which the young filaments grow in radially arranged groups.�

The nodules which are apparently formed by species of this genus occur in various sizes and shapes; Bornemann describesnbsp;one hemispherical mass 8 cm. hroad and 4 cm. thick. In some

cases the organism has given rise to oolitic spherules, which in radial section exhibit the branched tubular cells spreadingnbsp;in fan-shaped groups from the centre of the oolitic grain. Thenbsp;section parallel to the surface of a nodule presents the appearancenbsp;of a number of circular or elliptical tubes cut across transverselynbsp;or more or less obliquely. The resemblance between the fossilnbsp;and a specimen of the recent species Zonatrichia calcivoranbsp;Braun, is certainly very close, but it is very difficult, in thenbsp;absence of material exhibiting more detailed structure than isnbsp;shown in the specimens described by Bornemann, to decide withnbsp;any certainty the true position of the fossil. The figures do notnbsp;enable us to recognise any trace of cells in the radiating tubes.nbsp;It is possible that we have in Zonatrichites an example of anbsp;Cyanophyceous genus in which only the sheaths of the filaments have been preserved. In any case it is probable that thisnbsp;Mesozoic species affords another instance of a fossil alga whichnbsp;has been responsible for certain oolitic or other structures innbsp;limestone rocks.

The species described by Bornemann was obtained from a Breccia near Bissau in Silesia, of Keuper age.

M. Renault has recently described certain minute structures in a Palaeozoic coprolite to which he gives the name Gloioconisnbsp;Borneti'^, and which he regards as a Permian gelatinous alganbsp;similar to the well-known recent genus Gloeocapsa. The appearances revealed in a section of the coprolite are interpreted by thisnbsp;author as a collection of small colonies of a unicellular gelatinousnbsp;alga in various stages of development. Renault�s figure showsnbsp;a spherical group of faintly outlined and cloudy bodies, mostnbsp;of which include one or two small dark spots. The latter arenbsp;regarded as the cells of the alga, and the surrounding cloudynbsp;substance is described as the gelatinous sheath. The absencenbsp;of a nucleus in these extremely minute fossil cells (8�10 /x innbsp;diameter) is referred to as an argument in favour of referringnbsp;the organism to the Cyanophyceae rather than to the Chloro-phyceae. It is possible that the ill-defined structure describednbsp;by Renault may be a petrified alga, but there is not sufficientnbsp;evidence to warrant a decided opinion; the absence of nucleinbsp;1 Eenault (96^ p. 4t6.

can hardly be taken seriously in such a case as this as an argument in favour of the Cyanophyceae.

Although our exact knowledge of fossil Cyanophyceae is extremely small, it is probable that such simple forms of plantsnbsp;existed in abundance during the past ages in the earth�snbsp;history. Several writers have expressed the opinion that thenbsp;blue-green algae may be taken as the modern representativesnbsp;of those earliest plants which first existed on an archaean land-surface. The living species possess the power of resisting unfavourable conditions in a marked degree, and are able to adaptnbsp;themselves to very different surroundings. Their occurrence innbsp;hot springs proves them capable of living under conditionsnbsp;which are fatal to most plants, and suggests the possibility ofnbsp;their occurrence in the heated waters which probably constitutednbsp;the medium in which vegetable life began. An interestingnbsp;example of the growth of blue-green algae under unfavourablenbsp;conditions was recorded in 1886 by Dr Treub' of the Buitenzorgnbsp;Cardens, Java. In 1883 a considerable part of the islandnbsp;Krakatoa, situated in the Straits of Sunda, between Sumatranbsp;and Java, was entirely destroyed by a terrific volcanic explosion. What remained had been reduced to a lifeless massnbsp;of hot volcanic ashes. Three years later, Treub visited thenbsp;island, and found that several plants had already establishednbsp;themselves on the volcanic rocks. Various ferns and floweringnbsp;plants were recorded in Treub�s description of this newlynbsp;established flora. It seemed that the barren rocky surfacenbsp;had been prepared for the more highly organised plants by thenbsp;action of certain forms of Cyanophyceae, which were able to livenbsp;under conditions which would be fatal to more complex types.

In the petrified tissues of fossil plants there are occasionally found small spherical vesicles, with delicate limiting membranes,nbsp;in the cavities of parenchymatous cells or in the elements ofnbsp;vascular tissue. Some of these spherical inclusions have beennbsp;described as possibly simple forms of endophytic algaesuch asnbsp;we are now familiar with in species of the Cyanophyceae andnbsp;other algae. So far, however, no recorded instance of suchnbsp;fossil endophytic algae is entirely satisfactory. Some of thenbsp;* Treub (88).nbsp;nbsp;nbsp;nbsp;� Williamson (88).

cells figured by Williamson as possibly algae, endophytic in the tissues of Coal-Measure plants, are no doubt thin-wallednbsp;vesicles which formed part of a highly vacuolated cell-contents.nbsp;Examples of such vesicles in living and fossil cells are shownnbsp;in fig. 42. The fact that the contents of living plant tissuesnbsp;have been erroneously described as endophytic organisms,nbsp;should serve as a warning against describing fossil endophytesnbsp;without the test of good evidence to support them.

The description of a fossil Nostoc by the late Prof. Heer' from the Tertiary rocks of Switzerland cannot be accepted asnbsp;a trustworthy example of a fossil plant, much less of a genusnbsp;of recent algae. The application of recent generic names tonbsp;fossils which are possibly not even organic must do more harmnbsp;than good.

It is impossible to draw a sharp line between the two subdivisions of the Schizophyta. The so-called Fission-Fungi or Bacteria differ from the Schizophyceae or Fission-Algae in thenbsp;cell-contents being either colourless, blood-red or green, butnbsp;never blue-green. We may regard the Bacteria, generally, asnbsp;the lowest forms of plants; they are extremely simple organismsnbsp;which have been derived from some primitive types whichnbsp;possessed the power of independent existence and containednbsp;chlorophyll�that important substance which enables a plantnbsp;to obtain its carbon first-hand from the carbon dioxide of thenbsp;atmosphere.

Bacteria may be briefly described as single-celled plants, and as de Bary suggested comparable in shape to a billiard ball,nbsp;a lead pencil or a corkscrew*. A single spherical or cylindricalnbsp;cell measures about 1/i in diameter I They occur either singlynbsp;or in filaments, or as masses of various shapes consisting ofnbsp;numberless bacterial cells. The nature and manner of life of

de Bary (87) p. 9. A good account of the Schizomycetes has lately been written by Migula in Engler and Prantl�s Pflanzenfamilien, Leipzig, 1896.

Bacteria, and their extraordinary power of successfully resisting the most unfavourable conditions, render it probable that theynbsp;constitute an extremely ancient group of organisms.

The wonderful perfection of preservation of many fossil plants enables us to investigate the contents of petrified cellsnbsp;and to examine in minutest detail the histology of extinctnbsp;plants. To those who are familiar with the possibilities ofnbsp;microscopical research as applied to silicified and calcifiednbsp;fossil tissues, it is by no means incredible that evidence has beennbsp;detected of the existence of Bacteria as far back in the historynbsp;of the earth as the Carboniferous and Devonian periods.

Were there no trustworthy records of the occurrence of Bacteria in Palaeozoic times, it would still be a natural supposition that these ubiquitous organisms must have been abundantlynbsp;represented. It has been suggested as a probable conclusion thatnbsp;some forms of Bacteria, which produced chemical changes in thenbsp;soil necessary for the nutrition of plants, must have existednbsp;contemporaneously with the oldest vegetation¹.

The paper-coal of Toula, which in some places reaches a thickness of 20 cm., is a plant-bed of exceptional interest. Itnbsp;differs from ordinary coal in being made up of numberless thinnbsp;brown-papery sheets associated with a darker coloured substancenbsp;largely composed of ulmic acid. Prof Zeiller^, in an interestingnbsp;account of the papery layers, has shown that they consist of thenbsp;cuticles of a Lepidodendroid plant, Bothrodendron. An examination of a piece of one of the sheets at once reveals the existencenbsp;of a regular network of which the walls of the meshes are thenbsp;outlines of the epidermal cells, the meshes being bridged acrossnbsp;by a thin light brown membrane which represents the layernbsp;of cuticularised cell-wall of each epidermal cell. At regularnbsp;intervals and disposed in a spiral arrangement, we find smallnbsp;gaps in the papery cuticle which mark the position of thenbsp;Bothrodendron leaves. These Palaeozoic cuticles are not petrified ; they are only slightly altered, and have retained the powernbsp;of swelling in water, being able to take up stains like recent

nbsp;nbsp;nbsp;James (93¹), translation of a paper by M. Perry in the Revue Myeologique,nbsp;1893.

tissues. It may reasonably be assumed that the persistent cuticles owe their preservation to a greater power of resistancenbsp;to destructive agents than was possessed by the other tissuesnbsp;of the plant. It is by no means unlikely, as Renault^ hasnbsp;recently suggested, that as the Bothrodendron stem-fragmentsnbsp;lay in the swamps or marshes the tissues were gradually eatennbsp;away by Bacteria, but the cuticles successfully resisted thenbsp;attacks of the bacterial saprophytes. The same observer hasnbsp;described what he regards as the actual organism which effectednbsp;this wholesale destruction, under the name Micrococcus Zeilleri.nbsp;He finds, after treating the cuticles with ammonia to removenbsp;the ulmic acid, that there occur numerous minute sphericalnbsp;bodies, each surrounded by a thin envelope, either singly or innbsp;groups on the surface of the cuticular membrane. These varynbsp;in size from �Oya to I/a in diameter. I have not been able tonbsp;detect any satisfactory proof of such Micrococci in specimensnbsp;of the paper-coal which were treated according to Renault�snbsp;method, but it is extremely probable that this unusual methodnbsp;of preservation of stem-cuticles is the result of selective bacterialnbsp;action.

Renault believes that some of the minute spherulitic structures which are seen in sections of decayed tissues ofnbsp;Palaeozoic plants owe their origin, in part, to the ravages ofnbsp;bacteria. The disorganisation of parenchymatous cells givesnbsp;rise to a gelatinous substance in which needle-like crystals ofnbsp;silica may be deposited, from a siliceous solution, in a matrixnbsp;which has resulted from bacterial activity. In some of thenbsp;sections of tissues figured by Renault^ the outlines of a fewnbsp;cells are still indicated by fragments of the partially decayednbsp;wall, while in other cells the walls have been completelynbsp;destroyed by Bacteria of which some are preserved in thenbsp;centre of the cell-area, forming a kind of nucleus to thenbsp;siliceous spherulites.

In addition to the Micrococcus described by Renault from the Toula paper-coal, there are a host of other forms which

1 Eenault (95^), (96i) p. 478, (96^) p. 106. (Several figures of the cuticles are given in these publications.)

have been minutely diagnosed and figured by Profs. Renault and Bertrand h These authors have discovered what they believenbsp;to be well-defined species of Micrococcus and Bacillus rangingnbsp;in age from Devonian to Jurassic. The material which hasnbsp;afforded the somewhat startling results of their investigationsnbsp;consists partly of the coprolites of reptiles and fishes, and ofnbsp;silicified and calcified plant tissues.

This Bacillus, which was discovered in sections of a Permian coprolite from Central France, has the form of cylindrical rodsnbsp;12�14/r in length, and 1'3�1'�/x broad, rounded at each end.nbsp;The rods occur either singly or occasionally, two or three individuals are joined end to end. Fig. 28 B represents a piece of onenbsp;of Renault and Bertrand�s sections; the small rods are clearlynbsp;seen lying in various directions in the homogeneous matrix

of the coprolite. Each individual is said to be surrounded by an extremely minute empty space ��p, in width, originallynbsp;occupied by the Bacillus membrane, the central rod representingnbsp;the mineralized cell-contents. In this example the petrifyingnbsp;substance was probably derived from the phosphate of calcium

Renault and Bertrand (94). See also Renault (95^) p. 3, (96^) p. 449, PI. Lxxxix. (96^) p. 94, and (96�) p. 280, fig. 3.

of bones which were attacked by Bacteria. I am indebted to Prof. Renault for an opportunity of examining specimens ofnbsp;this and other fossil Bacteria, and in this particular case therenbsp;is undoubtedly strong evidence in favour of the author�s determination.

Renault has given the name Bacillus Tieghemi to certain minute rods 6�10,u, in length, and 2'2�3�8/i broad, oftennbsp;containing a dark coloured spherical spore-like body innbsp;diameter, which have been found in the tissues of a Coal-Measure plant.

The name Micrococcus Guignardi has been applied to more or less spherical bodies 2'2/x in diameter, also met with innbsp;silicified plants.

A portion of one of Renault�s figures is reproduced in Fig. 28 A. The faint and broken lines mark the position of thenbsp;middle lamellae of parenchymatous cells from the pith of anbsp;Calamite. The tissue has been almost completely destroyed,nbsp;but the more resistant middle lamellae have been partiallynbsp;preserved. The short and broad rods represent what Renaultnbsp;terms Bacillus Tieghejni; the small circle in the middle of somenbsp;of these being referred to as a spore, and in one specimennbsp;shown in the figure, the second rod at right angles to thenbsp;first is described as a small daughter-Bacillus formed by thenbsp;germination of the central spore.

It is unnecessary to give an account of the numerous examples of Micrococci and Bacilli described by Renault fromnbsp;Devonian, Carboniferous, Permian and Jurassic rocks. We may,nbsp;however, in a few words consider the general question of thenbsp;existence and possible determination of fossil Bacteria.

In 1871 Prof. Van Tieghem^ of Paris drew attention to the method of operation and plan of attack of Bacillus amylohacter

^ Eenault (95^) p. 17, fig. 9, (96') p. 460, fig. 102, and (96^) p. 292, fig. 10.

as a destructive agent in the decay of plant d�bris in water. He was able to follow the gradual disorganisation of the tissuesnbsp;and the various steps in the � butyric fermentation � effected bynbsp;this Bacterium. Similarly the same author� was able to detectnbsp;the action of an allied organism in some silicified tissues fromnbsp;the Carboniferous nodules of Grand-Croix, a well-known localitynbsp;for petrified plants near Saint-�tienne. He recognised also thenbsp;traces of the Bacillus itself in the partially destroyed plantnbsp;tissues. The Palaeozoic Bacteria made use of some cellulosedissolving ferment of which the action is clearly demonstratednbsp;in sections of silicified tissues. Many of the phenomenanbsp;described by Renault and Bertrand as due to similar Bacterialnbsp;action, afford additional evidence that the gradual disorganisationnbsp;of vegetable tissues was effected in precisely the same mannernbsp;as at the present day.

In some cases we have I believe trustworthy examples of the Bacteria themselves, both in coprolites and plant-tissues,nbsp;but it is more than probable that some of the recorded examplesnbsp;are not of any scientific value. The examination of petrifiednbsp;tissues under the higher powers of a microscope often reveals the existence of numerous spherical particles and rodlike bodies which agree in shape with Micrococci or Bacilli.nbsp;Minute crystals of mineral substances may occur in the siliceousnbsp;or calcareous matrix of a petrified plant which simulate minutenbsp;organic forms. Vogelsang^ in his important work die Krystal-liten has thrown considerable light on the ontogeny of crystals,nbsp;and the minute globulites and other forms of incipient crystallisation might well be mistaken for Bacterial cells. Granting,nbsp;however, that we have satisfactory evidence, both direct andnbsp;indirect, that some forms of Bacteria lived in the decayingnbsp;tissues of Palaeozoic plants, and in the intestines of reptilesnbsp;and other animals, we cannot safely proceed to specific diagnosesnbsp;and determinations ^

� I am indebted to Prof. Kantbaek for calling my attention to an interesting account of Bacilli in small stones found in gall-bladders; a manner of occurrencenbsp;comparable to that of the fossil forms in petrified tissues. Vide Naunyn (96)nbsp;p. 51.

Renault has pointed out that fossil Bacteria may often be more readily detected than living forms owing to the presencenbsp;of a brown ulmic substance which results from the carbonisationnbsp;of the protoplasm. He is forced to admit, however, that suchnbsp;diagnostic characters as are obtained by Bacteriologists by meansnbsp;of cultures cannot be utilised when we are dealing with fossilnbsp;examples! We are told that �Partout oil nous avons cherch�nbsp;des Bacteriace�s, nous en avons rencontr�.� ^ This indeed isnbsp;the danger; an extended examination of fossil sections undernbsp;an immersion-lens must almost inevitably lead to the discoverynbsp;of minute bodies of a more or less spherical form which mightnbsp;be Micrococci. To measure, and name such bodies as definitenbsp;species of Micrococci is, I believe, but wasted energy and annbsp;attempt to compass the impossible.'

Specialists tell us that the accurate determination of species of recent Bacteria is practically hopeless: may we not reasonablynbsp;conclude that the attempt to specifically diagnose fossil formsnbsp;is absolutely hopeless ?nbsp;nbsp;nbsp;nbsp;� The imagination of man is naturally

sublime, delighted with whatever is remote and extraordinary��, but it is to he deplored if the fascination of fossil bacteriology is allowed to warp sound scientific sense.

The presence of chlorophyll is one common characteristic of the numerous plants included in the Algae. The generallynbsp;adopted classification rests in pai't on an artificial distinction,nbsp;namely the prevailing colour of the plant.

It must be definitely admitted, at the outset, that palaeo-botany has so far afforded extremely little trustworthy information as to the past history of algae. Were we to measure

the importance of the geological history of these plants by the number of recorded fossil species, we should arrive at a totallynbsp;wrong and misleading estimate. By far the greater numbernbsp;of the supposed fossil algae have no claim to be regarded asnbsp;authentic records of this class of Thallophytes. It has beennbsp;justly said that palaeontologists have been in the habit ofnbsp;referring to algae such impressions or markings on rocks asnbsp;cannot well be included in any other group. � A fossil alga,�nbsp;has often been the dernier ressort of the doubtful student.

Before discussing our knowledge, or rather lack of knowledge, of fossil algae at greater length, it will be well to briefly consider the manner of occurrence and botanical nature of existing forms. In the sea and in fresh water, as well as in dampnbsp;places and even in situations subject to periods of drought,nbsp;algae occur in abundance in all parts of the world. We findnbsp;them attaining full development and reproducing themselves atnbsp;a temperature of � 1� C. in the Arctic Seas, and again living innbsp;enormous numbers in the waters of thermal springs. Aroundnbsp;the coast-line of land areas, and on the floor of shallow seasnbsp;algae exhibit a remarkable wealth of form and luxuriance ofnbsp;growth. As regards habit and structure, there is every gradation from alsfae in which the whole individual consists of anbsp;thin-walled unseptate vesicle, to those in which the thallusnbsp;attains a length unsurpassed by any other plant, and of whichnbsp;the anatomical features clearly express a well-marked physiological division of labour such as occurs in the highest plants.

The large and leathery seaweeds which flourish in the extreme northern and southern seas are plants which it isnbsp;reasonable to suppose might well have left traces of theirnbsp;existence in ancient sediments. Sir Joseph Hooker, in hisnbsp;account of the Antarctic florah investigated during Sir Jamesnbsp;Ross�s voyage in H.M. ships Erebus and Terror, has givennbsp;an exceedingly interesting description of the gigantic brownnbsp;seaweeds of southern latitudes. The trunks are described asnbsp;usually 5�10 feet long, and as thick as a human thigh, dividingnbsp;towards the summit into numerous pendulous branches whichnbsp;are again broken upjnto sprays with linear �leaves.� Hookernbsp;� Hooker, J. D. (44) p. 457. Pis. OLxvii. clxviii. and clxxi. D.

records how a captain of a brig employed his crew for two bitterly cold days in collecting Lessonia stems which had beennbsp;washed up on the beach, thinking they were trunks of trees fitnbsp;for burning. On our own coasts we are familiar with thenbsp;common Laminaria, the large brown seaweed with long andnbsp;strap-shaped or digitate fronds which grows on the rocks belownbsp;low-tide level. The frond passes downwards into a thick andnbsp;tough stipe firmly 'attached to the ground by special holdfasts.nbsp;A transverse section of the stalk of a fairly old plant presentsnbsp;an appearance not unlike that of a section of a woody plant.nbsp;In the centre there is a well-defined axial region or pithnbsp;consisting of thick walled, long and narrow tubes pursuing anbsp;generally vertical though irregular course, and embedded in anbsp;matrix of gelatinous substance derived from the mucilaginousnbsp;degeneration of the outer portions of the cell-walls. The greaternbsp;part of such a section consists, however, of regularly disposed

activity of a zone of dividing or meristematic elements. The occurrence of distinct concentric rings in this secondary tissuenbsp;clearly points to some periodicity of growth which is expressednbsp;by the alternation of narrow and broader cells. In the Antarctic genus Lessonia, the stem reaches a girth equal to that ofnbsp;a man�s thigh, and in structure it agrees closely with the smallernbsp;stem of Laminaria. In these large algal stems, the cells arenbsp;not lignified as in woody plants, and in longitudinal sectionnbsp;they have for the most part the form of somewhat elongatednbsp;parenchyma, differing widely in appearance from the tracheidsnbsp;or vessels of woody plants. At the periphery of the Laminarianbsp;stem, represented in fig. 29, there occur numerous and comparatively large mucilage ducts.

In certain algae of different families the thallus is encrusted with carbonate of lime, and is thus rendered much morenbsp;resistant. The Diatoms, on the other hand, possess still morenbsp;durable siliceous tests which are particularly well adapted tonbsp;resist the solvent action of water and other agents of destruction.nbsp;It is these calcareous and siliceous forms which supply thenbsp;greater part of the trustworthy data furnished by fossil algae.

It remains to consider some of the causes to which we may attribute the scarcity of fossil algae, and the possible sourcesnbsp;of error which beset any attempt to describe or assign namesnbsp;to impressions and casts simulating algal forms.

In the first place, the delicate nature of algal cells is a serious obstacle to fossilisation. Even in plants in which thenbsp;woody stems have been preserved by a siliceous or calcareousnbsp;solution, we frequently find the more delicate cells represented by a mass of crystalline matter without any trace of thenbsp;cell-walls being preserved. In such plants as algae, wherenbsp;the cell-walls are not lignified, but consist of cellulose or somenbsp;special form of cellulose, which readily breaks down into anbsp;mucilaginous product, the tissues have but a small chance ofnbsp;withstanding the wear and tear of fossilisation.

The danger of relying on external form as a means of recognition is especially patent in the case of those numerousnbsp;markings or impressions frequently met with on rocks, andnbsp;which resemble in outline the thallus of recent algae. Among

animals, such as certain Polyzoa, the flat branching body of various algae is closely simulated, and in other plants, such asnbsp;the frondose liverworts, the same thalloid and branched formnbsp;of body is again met with. Some of the much dissectednbsp;Aphlebia leaves of ferns (e.g. Rhacophyllum species) bear anbsp;striking resemblance to fossil algae; and numerous othernbsp;examples might be quoted. In palaeobotanical literature wenbsp;find a host of names, such as Chondrites, Fucoides^, Caulerpitesnbsp;and others applied to indefinite and indistinct surface markingsnbsp;which happen to resemble in shape certain of the betternbsp;known genera of recent seaweeds.

The close parallelism in outward form displayed by different genera and families of algae is in itself sufficient argumentnbsp;against the use of recent generic names for fossils of whichnbsp;the algal nature is often more than doubtful. Were externalnbsp;form to be accepted as a trustworthy guide, in the absencenbsp;of internal structure and reproductive organs, such a genusnbsp;as Caulerpa^ would afford material for numerous genericnbsp;designations. A comparison of the different species of thisnbsp;Siphoneous green alga brings out very clearly the exceedinglynbsp;protean nature of this interesting genus, and serves as onenbsp;�instance among many of the small taxonomic value whichnbsp;can be attached to external configuration. Caulerpa pusillanbsp;Mart, and Her., G. taxifolia (VahL), G. pluriiaris Forsk.,nbsp;C. abies-marina J. Ag., C. ericifolia (Turn.), C. hypnoidesnbsp;(R. Br.), C. cactoides (Turn.), G. scalpelli formis (R. Br.), andnbsp;others clearly illustrate the almost endless variety of form exhibited by the species of a single genus of algae. We constantlynbsp;find in the several classes of plants a repetition of the samenbsp;form either in the whole or in the separate members of thenbsp;vegetative body, and but a slight acquaintance with plantnbsp;types should lead us to use the test of external resemblancenbsp;with the greatest possible caution. To emphasize this dangernbsp;may seem merely the needless reiteration of a self-evident fact,

^ An American writer has recently discussed the literature and history of Fucoides; he gives a list of 85 species. It is very doubtful if such work as thisnbsp;is worth the labour. (James [93].)

but there is, perhaps, no source of error which has been more responsible for the creation of numerous worthless species amongnbsp;fossil plants.

There is, however, another category of impressions and casts of common occurrence in sedimentary rocks which requires anbsp;brief notice. Very many of the fossil algae described in textbooks and palaeobotanical memoirs have been shown to be ofnbsp;animal origin, and to be merely the casts of tracks and burrows.nbsp;A few examples will best serve to illustrate the identity of manynbsp;of the fossils referred to algae with animal trails and withnbsp;impressions produced by inorganic agency.

Dr Nathorst of Stockholm has done more than any other worker to demonstrate the true nature of many of the species ofnbsp;Chondrites, Gruziana, Spirophyton, Eophyton, and numerousnbsp;other genera. In 1867 there were discovered in certainnbsp;Cambrian beds of Vestrogothia, long convex and furrowednbsp;structures in sandstone rocks which were described as thenbsp;remains of some comparatively highly organised plant, andnbsp;described under the generic name Eophyton^. By manynbsp;authors these fossils have been referred to algae, but Nathorstnbsp;has shown that the frond of an alga trailed along the surfacenbsp;of soft plaster of Paris produces a finely furrowed groovenbsp;(fig. 30,2) which would afford a cast similar to that of Eophyton.nbsp;The same author has also adduced good reasons for believingnbsp;that the Eophytons of Cambrian rocks may represent the trailsnbsp;made by the tentacles of a Medusa having a habit similar to thatnbsp;of Polydonia frondosa Ag. Impressions of Medusae have beennbsp;described by Nathorst from the beds in which Eophyton occurs;nbsp;and the specimens in the Stockholm Museum afford a remarkable instance of the rare preservation of a soft-bodied organism^nbsp;By allowing various animals to crawl over a soft-prepared surfacenbsp;it is possible to obtain moulds and casts which suggest in anbsp;striking manner the branched thallus of an alga. The tracks ofnbsp;the Polychaet, Goniada maculata Orstd.�, one of the Glyceridae,nbsp;are always branched and very algal-like in form (fig. 30, 3).

1 Linnarsson (69) PI. xi. fig. 3. There are many good specimens of this fossil in the Geological Survey Museum, Stockholm.

Many of the so-called fossil algae are undoubtedly mere tracks or trails of this type. In the fossil-plant gallery of the Britishnbsp;Museum there are several specimens of small branched casts,nbsp;clearly marked as whitish fossils on a dark grey rock of Uppernbsp;Greensand age from Bognor; these were described by Mantellnbsp;and Brongniart^ as an alga, but there is little doubt of theirnbsp;being of the same category as the track shown in fig. 30, 3.

The well-known half-relief casts met with in Cambrian, Silurian and Carboniferous rocks, and known as Gruziana or Bilobites, are probably casts of the tracks of Crustaceans. The impressionnbsp;left by a King-Crab (Limulus) as it walks over a soft surfacenbsp;affords an example of this form of cast. It has been suggestednbsp;that some of the Bilobites may be the casts of an organism likenbsp;Balanoglossus'^, a worm-like animal supposed by some to havenbsp;vertebrate affinities. The resemblance between some of thenbsp;loM^er Palaeozoic Bilobites and the external features of a Balano-glossus is very striking, and such a comparison is worth considering in view of the fact that soft-bodied animals have occasionallynbsp;left distinct impressions on ancient sediments.

The literature on the subject of fossil algae versus inorganic and animal markings is too extensive and too wearisome tonbsp;consider in a short summary; the student will find a sufficientnbsp;amount of such controversial writing�with references tonbsp;more�in the works quoted belowh

In the Stockholm Museum of Palaeobotany there is an exceedingly interesting collection of plaster casts obtained bynbsp;Dr Nathorst in his experiments on the manufacture of fossilnbsp;� algae,� which afford convincing proof of the value andnbsp;correctness of his general conclusions.

The pressure of the hand on a soft moist surface produces a raised pattern like a branched and delicate thallus. The well-known Oldhamia antiqua Forbes and Oldhaniia radiata Forbes^,nbsp;from the Cambrian rocks of Irelailtl may, in part at least, owenbsp;their origin to mechanical causes, and we have no sufficient

' Mantell (33) p. 166. Vide also Morris (54) p. 6. nbsp;nbsp;nbsp;^ Bateson (88).

� Nathorst (81), (86) amp;o. Dawson (88) p. 26 et seq. Dawson (90) Delgado (86) �WUliamson (85) Hughes (84) Zeiller (84) Saporta (81) (82) (84) (86) Fuchs (95)nbsp;Sothpletz (96).nbsp;nbsp;nbsp;nbsp;4 Kinahan (58).

evidence for including them among the select class of true fossil algae. Sollas^ has shown that the structure known asnbsp;Oldhamia radiata is not merely superficial but that it extendsnbsp;across the cleavage-planes. Oldhamia is recorded from Lowernbsp;Palaeozoic rocks in the Pyrenees^ by Barrois, who agrees withnbsp;Salter, Goppert and others in classing the fossil among thenbsp;algae. The photograph accompanying Barrois� description doesnbsp;not, however, add further evidence in favour of accepting Oldhamia as a genus of fossil algae.

The burrows made by Gryllotalpa vidgaris Latr., the Mole-cricket, have been shown by Zeiller to bear a close resemblance to a branch of a conifer in half-relief (fig. 30, 4), or to such anbsp;supposed algal genus as Phymatoderma^.

In fig. 30,1, we have what might well be described as a fossil alga. This is merely a cast of a miniature river-system such asnbsp;one frequently sees cut out by the small rills of water flowingnbsp;over a gently-sloping sandy beach. A cast figured and described by Newberry as an alga, Dendrophycus triassicus*, fromnbsp;the Trias of the Connecticut Valley, is practically identical withnbsp;the rill-marks shown in fig. 30,1. The cracks produced in drying

Fia. 31. Chondrites verisiviilis Salt. Wenlook limestone, Dudley. From a specimen in the British Museum (V. 2350). Slightly reduced.

and contracting sediment may form moulds in which casts are subsequently produced by the deposition of an overlying layernbsp;of sand, and such casts have been erroneously referred to algalnbsp;1 Sollas (86).

� Barrois (88). Eeferences to other records of this genus may be found in Barrois� paper.

** Newberry (88) p. 82, PI. xxi. There are some large specimens of this supposed alga in the National Museum, Washington; they are undoubtedly ofnbsp;the nature of rill-marks.

impressions \ Dawson^ has figured two good examples of Carboniferous rill-marks from Nova Scotia in his paper onnbsp;Palaeozoic burrows and tracks of invertebrate animals.

The specimen represented in fig. 31 affords an example of a fairly well-known fossil from the Wenlock limestone, originallynbsp;described by Salter as Chondrites verisimilis Salt, from Dudley�.nbsp;He regarded it as an alga, and the graphitic impression agreesnbsp;closely in form with the thallus of some small seaweeds. Anbsp;closer examination of the fossil reveals a curious and characteristic irregular wrinkling on the graphite surface, which suggestsnbsp;an organism of more chitinous and firmer material than that ofnbsp;an alga.

A similar and probably an identical fossil is described and figured by Lapworth^ in an appendix to a paper by Walternbsp;Keeping on the geology of Central Wales, under the namenbsp;of Odontocaulis Keepingi Lap. and regarded as a dendroidnbsp;graptolite. In any case we have no satisfactory grounds fornbsp;including these fossils in the plant-kingdom.

How then are we to recognise the traces ot ancient algae? There is no golden rule, and we must admit thenbsp;difficulty of separating real fossil algae from markings made bynbsp;animal or mechanical agency. The presence of a carbonaceousnbsp;film is occasionally a help, but its occurrence is no sure test ofnbsp;plant origin, nor is its absence a fatal objection to an organicnbsp;origin. While being fully alive to the small value of externalnbsp;resemblance, and to the numerous agents which have beennbsp;shown to be capable of producing appearances indistinguishablenbsp;from plant impressions, we must not go too far in a purelynbsp;negative direction.

An important contribution to the subject of fossil algae has lately appeared by Prof. Rothpletz�. He deals more particularlynbsp;with the much discussed Flysch� Fucoids of Tertiary age, andnbsp;while refusing to accept certain examples as fossil algae, henbsp;brings forward weighty arguments in favour of including severalnbsp;other forms among the algae. He is of opinion that most of the

1 Vide �Williamson (85). nbsp;nbsp;nbsp;^ Dawson (90) p. 615.nbsp;nbsp;nbsp;nbsp;� Salter (73) p. 99.

� A term applied to a certain facies of Eocene and Oligocene rocks in Central Europe.

main divisions of the algae are represented among the Flysch Fucoids, but considers that the Phaeophyceae are the mostnbsp;numerous.

Rothpletz�s work is chiefly interesting as illustrating the application of microscopic examination and chemical analysis tonbsp;the determination of fossil algae. Although he makes out anbsp;good case in favour of restoring many of the Tertiary fossils tonbsp;the plant kingdom, the material at his disposal does not admitnbsp;of satisfactory botanical diagnosis.

No doubt some of the fossils from the Silurian and Cambrian rocks are true algae, and Nathorst has pointed out that such anbsp;species as Hall�s Sphenothallus angustifolius^ may well be an alga.nbsp;Additional examples might be quoted from Bornemann andnbsp;other writers, but in view of the attempts which are sometimesnbsp;made to trace the development of more recent plants to morenbsp;than doubtful Lower Palaeozoic Algae, one must agree withnbsp;Nathorst�s opinion,��Je crois que Ton rend un bien mauvaisnbsp;service a la th�orie de l��volution, en essayant de baser l�arbrenbsp;g�n�alogique des algues fossiles sur des corps aussi douteuxnbsp;que les Bilobites, Crossochorda, Eophyton, etc.^�

There are many carbonaceous impressions on rocks of different ages which it is reasonable to refer to algal origin,nbsp;and although such are of little or no botanical value, it may benbsp;a convenience to refer to them under a definite term. Thenbsp;comprehensive generic name Algites^ has been suggested asnbsp;a convenient designation for impressions or casts which arenbsp;probably those of algae.

Some of the fossils described by Mr Kidston from British Carboniferous rocks as probably algae present an undoubtednbsp;algal appearance, and might be placed in the genus Algites;nbsp;but in some cases�e.g. Chondrites plumosa^ Kidst. from thenbsp;Calciferous Sandstone of Eskdale, one feels much more doubtful;nbsp;in this particular instance the impressions suggest the finenbsp;roots of a water-plant.

^ Kidston (83) PI. xxxii. fig, 2. Specimens of this form may be seen in the British Museum collection.

The statement is occasionally made that the numerous fossil algae and the absence of higher plants in the older stratanbsp;justify the description of the oldest rocks as belonging to thenbsp;� age of algae.� Such an assertion rests on an unsound basis, andnbsp;is rather the expression of what might be expected than whatnbsp;has been proved to be the case. The oldest plants with whichnbsp;we are at all closely acquainted are of such a type as to forciblynbsp;suggest that in the lowest fossiliferous rocks we are still verynbsp;far from the sediments of that age which witnessed the dawnnbsp;of plant life.

Many of the obscure markings on rock surfaces which have been referred to existing genera of algae or described as newnbsp;genera, are much too doubtful to be included even under such anbsp;comprehensive name as Algites. Space does not admit ofnbsp;further reference to determinations of this type which aboundnbsp;in palaeontological literature.

It would be very difficult to produce satisfactory evidence for the algal nature of many of the supposed fossil algae fromnbsp;Cambrian rocks'; there has been a special tendency to recognise'nbsp;algal remains in the oldest fossiliferous strata, due in part nonbsp;doubt to the fallacy that in that period nothing higher thannbsp;Thalloph3des is likely to have existed. The go-called Phycodesnbsp;referred to by Credner^ as characteristic of the Cambrian rocksnbsp;of the Fichtelgebirge (� Phycoden-Schiefer �) is probably ofnbsp;inorganic origin, and comparable to the genus Vexillum ofnbsp;Saporta� and other writers, which Solms-Laubach has describednbsp;as being formed every day in the soft mud of our ponds wherenbsp;local currents are checked bj' branches and other obstaclesquot;.nbsp;There are several good specimens of Phycodes in the Berg-akademie of Berlin and in the Leipzig Museum which, I believe,nbsp;clearly demonstrate the absence of all satisfactory evidence ofnbsp;an algal origin.

We may next pass to a short description of a few representative types of algae, which may reasonably be classed under

Cf. Matthew, G. F. (89). Hall called attention in 1852 to the prevalent habit of describing �algae� from the older strata, without any evidence for anbsp;vegetable origin. (Hall [52] p. 18.)

This family occupies a somewhat isolated position among the algae, and is best considered as a distinct subdivision rathernbsp;than as a family of the Phaeophyceae or Brown algae, withnbsp;which it possesses as a common characteristic a brown-colouringnbsp;matter.

Single-celled plants consisting of a simple protoplasmic body containing a nucleus and brown colouring matter (diatomin)nbsp;associated with the chlorophyll. The cell-wall is in the form ofnbsp;two halves, known as valves, which fit into one another like thenbsp;two portions of a pill-box. The cell-wall contains a largenbsp;amount of silica, and the siliceous cases of the diatoms arenbsp;commonly spoken of as the valves of the individual, or thenbsp;frustules. Diatoms exhibit a characteristic creeping movement,nbsp;and are reproduced by division, also by the development ofnbsp;spores in various formsh

The recent members of the family have an exceedingly wide distribution, occurring both in freshwater and in the sea.nbsp;Owing to the lightness of the frustules, they are frequentlynbsp;carried along in the air, and atmospheric dust falling on shipsnbsp;at sea has been found to contain large numbers of diatoms^nbsp;The siliceous valves are abundant in guano deposits, and theynbsp;have been found also in association with volcanic material.nbsp;Diatomaceous deposits are now being formed in the Yellowstonenbsp;Park district; � they cover many square miles in the vicinity ofnbsp;active or extinct hot spring vents of the park, and are oftennbsp;three feet, four feet, and sometimes five to six feet thick�.��nbsp;The gradual accumulation of the siliceous tests on the floor of anbsp;fresh-water lake results in the formation of a sediment consistingnbsp;in part of pure silica. Such deposits, often spoken of as kieselguhr

' A monograph on the Diatomaoeae has recently been written by Schiitt for Engler and Prantl�s systematic work. See also Murray, G. (97) and Pfitzer (71).

or diatomite, and used as a polishing material, occur in many parts of Britain, marking the sites of dried-up pools or lakes.nbsp;At the northern end of the island of Skye there occurs annbsp;unusually pure deposit of diatomite overlain by peat and turf,nbsp;and extending over an area of fifty-eight square miles. Manynbsp;of the individuals in this deposit were in all probability carriednbsp;into the lake by running water, while others lived in the lakenbsp;and after death their tests contributed to the siliceous deposit!nbsp;The late Dr Ehrenberg published numerous papers on dia-tomaceous deposits in different parts of the world, and in hisnbsp;great work, Zur Mikrogeologie^, he gave numerous and beautifully executed illustrations of such siliceous accumulations. Innbsp;many of the samples he figures one sees fragments of plantnbsp;tissues, spores of conifers and ferns, associated with thenbsp;diatom tests. The occurrence of the pollen grains of coniferous trees in lacustrine and marine deposits is not surprisingnbsp;in view of their abundance in Lake Constance and other lakes.nbsp;It is stated that the pollen of conifers in the Norwegian fiordsnbsp;plays an important part in the nourishment of the Rhizopod^nbsp;Saccamina^.

In the waters of the ocean diatoms are of frequent occurrence, and very widely distributed. Sir Joseph Hooker records thenbsp;existence of masses of diatomaceous ooze over a wide area innbsp;Antarctic regions^. Along the shores of the Victoria Barrier, anbsp;perpendicular wall of ice, between one and two hundred feetnbsp;above sea-level, the soundings were found to be invariablynbsp;charged with diatom remains, and from the base of the ice-wallnbsp;there appeared to be in process of formation a bank of thesenbsp;tests stretching north for a distance of 200 miles. The morenbsp;extended researches conducted during the cruise of thenbsp;Challenger have clearly proved the enormous accumulationsnbsp;of diatoms now being formed on the ocean-bed�. South ofnbsp;latitude 45� S. there is now being built up a vast depositnbsp;which may be eventually upraised as a fairly pure siliceousnbsp;rock. From extreme northern latitudes Nansen has recently

recorded the occurrence of these lowly organised plants. He writes,�� I found a whole world of diatoms and other microscopical organisms, both vegetable and animal, living in thenbsp;fresh-water pools on the Polar drift-ice, and constantly travellingnbsp;from Siberia to the east coast of Greenland'.� In warmernbsp;latitudes diatoms abound in the surface waters, but therenbsp;they are associated with numerous other forms of the Planktonnbsp;vegetation. The waters of the Amazon carry with them intonbsp;the sea large numbers of fresh-water forms, which are floatednbsp;out to sea and finally added to the rock-building material whichnbsp;is constantly accumulating on the ocean floorl No definitenbsp;results have so far been obtained as to the geographical andnbsp;bathymetrical distribution of marine diatoms.

The enormous number of recent species precludes any attempt to give a description of the better-known forms. Itnbsp;is more important for us to realize how common and widelynbsp;distributed are the living genera. The hard and almostnbsp;indestructible valves have been frequently found in a fossilnbsp;condition, often forming thick and extensive masses of siliceousnbsp;rock. From diatom-beds now forming in lakes and on thenbsp;ocean-bed we pass to deposits such as those in Skye andnbsp;elsewhere, which mark the site of recently dried-up sheets ofnbsp;water, and so to older rocks of Tertiary age formed undernbsp;similar conditions. Among the many examples of diatomaceousnbsp;deposits of Tertiary and Cretaceous age mention should benbsp;made of those of Berlin, K�nigsberg, Bilin in Bohemia, andnbsp;Richmond in Virginia. The diatoms in the beds of Berlin arenbsp;regarded as fresh-water, and those of Richmond as marine. Itnbsp;has been pointed out by Pfitzer that it is a comparatively easynbsp;matter to distinguish between fresh-water and marine formsnbsp;of diatoms. The diatomaceous rocks of Bilin are known asnbsp;polishing slates; they attain a thickness of 50 feet. In these,nbsp;as in many other cases, the deposit has become cementednbsp;together as a hard flinty or glassy rock, in which the cementingnbsp;material was formed by the solution of some of the diatomnbsp;tests^. In many cases in which calcareous and siliceous rocks

reveal no direct evidence of organic origin it is probable that they were originally formed by the accumulation of plants ofnbsp;which the structure has been completely obliterated by secondarynbsp;causes. The genus Gallionella plays an important part in thenbsp;composition of the Bilin beds. Occasionally impressions ofnbsp;leaves and other organic remains are found associated withnbsp;the diatoms in the siliceous rocks. In the British Museumnbsp;(Botanical department) a large block of white powdery rock isnbsp;exhibited as an example of a diatomaceous deposit of Tertiarynbsp;age from Australia. It is described as being largely madenbsp;up of the tests of fresh-water diatoms, such as Navicula,nbsp;Qomphonema, Cymhella, Synedra, and others.

The abundance of Diatoms in Cretaceous rocks of the Paris basin has recently been recorded by Cayeux'^; it would seemnbsp;that these algae had already assumed an important role asnbsp;rock-builders in pre-Tertiary times. Cayeux points out thatnbsp;the silica of these Cretaceous diatomaceous frustules has oftennbsp;been replaced by carbonate of calcium.

In addition to the occurrence of Diatoms in the various diatomaceous deposits, their siliceous tests may occasionally benbsp;recognised in argillaceous or other sediments. Shrubsole andnbsp;Kitton^ have described several species of Diatoms from thenbsp;London Clay of Lower Eocene age. In many localities in thenbsp;London basin the clay obtained from well-sinkings presentednbsp;the appearance of being dusted with sulphur-like particles of anbsp;dark bronze or golden colour which glistened in the sunlight.nbsp;These yellow bodies have been found to be diatomaceousnbsp;frustules in which the silica has been replaced by iron pyrites.nbsp;The genus Coscinodiscus is one of the commonest forms recordednbsp;from the London Clay*.

Without further considering individual examples of diatomaceous rocks we may briefly notice the general facts of the geological history of the family. As Ehrenberg pointednbsp;out several years ago, the Tertiary and Cretaceous species ofnbsp;diatoms show a very marked resemblance to living forms. In

many cases the species are identical, and the fossil deposits as a whole seem to differ in no special respect from those nownbsp;being built up.

With the exception of two species of Liassic Diatoms, no trustworthy examples of the Diatomaceae have been foundnbsp;below the Cretaceous series. The oldest known Diatoms werenbsp;discovered by Rothpletz^ among the fibres of an Upper Liasnbsp;sponge from Boll in Wtirtemberg. They occur as smallnbsp;thimble-shaped siliceous tests with coccoliths and foraminiferanbsp;in the horny skeleton of Phymatoderma, a genus formerlynbsp;regarded as an alga. Rothpletz describes two species whichnbsp;he includes in the genus Pyxidicula, P. hollensis and P. liasica.nbsp;This generic name of Ehrenberg is used by Schiitt^ as a subgenus of Stephanopyxis.

Seeing how great a resemblance there is between the recent and Cretaceous species, and how many examples there are ofnbsp;Tertiary diatom deposits, it is not a little surprising that the pastnbsp;history of these plants has not been traced to earlier periods.nbsp;In 1876 Castracane��, an Italian diatomist, gave an account ofnbsp;certain species of diatoms said to have been found in a block ofnbsp;coal from Liverpool obtained from the English Coal-Measures.nbsp;The species were found to be identical with recent forms. Itnbsp;is generally agreed that these specimens cannot have beennbsp;from the coal itself, but that they must have been living formsnbsp;which had come to be associated with the coal. The late Prof.nbsp;Williamson spent many years examining thin sections andnbsp;other preparations of coal from various parts of the world, butnbsp;he never found a trace of any fossil diatom. There is nonbsp;apparent reason why diatoms should not be found in Pre-Cretaceous rocks, and the microscopic investigation of oldnbsp;sediments may well lead to their discovery. Prof. Bertrandnbsp;of Lille, who has devoted himself for some time past to a detailednbsp;microscopical examination of coal, informs me that he has sonbsp;far failed to discover any trace of Palaeozoic diatomaceous tests.

The genus Bactryllium is often quoted in text-books as a probable example of a Triassic diatom. It was first described

by Heer* from the Trias of Switzerland and North Italy, also from the neighbourhood of Heidelberg, and regarded as annbsp;extinct member of the Diatomaceae. Heer defined the genusnbsp;as follows:

�Small bodies, with parallel sides, rounded at either end, the surface traversed by one or two longitudinal grooves.�

(fig. 32, C.) Several species have been figured by Heer from beds of Muschelkalk, Keuper and Rhaetic age. He describesnbsp;the wall as thick and firm (fig. 32, C. ii.) and probably com-

1^10.32. A, Lithothamnion mamillosum Gixmh. (i) In section, (ii) surface view [after Giimbel. (i) x 320, (ii) nat. size]. B, Sycidium melo Sandb.nbsp;(i) Surface view, (ii) transverse section (after Deecke). C, Bactrylliumnbsp;deplanatum Heer. (i) Surface view, (ii) section, showing the thick wallnbsp;and hollow interior (after Heer). D, Calcareous pebble from a lake innbsp;Michigan. Kather less than nat. size (after Murray).

posed of silica, with a hollow interior. The specimen shown in fig. 32, C. was found in the Rhaetic beds, and named by Heernbsp;Bactryllium deplanatum] it has a length of 4'5 mm.; thenbsp;surface is transversely striated and traversed by a single longitudinal groove. Stefani^ has given reasons in favour of removing

Bactryllium from the plant to the animal kingdom; he points out that the specimens are too large for diatoms, and moreovernbsp;that they are asymmetrical in form and possessed a calcareousnbsp;and not a siliceous shell. He would place the fossil amongnbsp;the Pteropods, comparing it with such genera as Guvierinanbsp;and Hyalaea. In view of Stefani�s opinion we cannot attachnbsp;any importance to this supposed diatom, especially as it hasnbsp;generally been regarded as at best but an unsatisfactory genus.

Thallus unseptate, having the form of a vesicle or a variously branched coenocyte, which may or may not be encrusted withnbsp;carbonate of lime, or of filaments composed of cells containing anbsp;single nucleus, or of cells in which more than one nucleusnbsp;occurs; in other instances consisting of a plate of cells ornbsp;a cell-mass. Asexual reproduction by zoospores and othernbsp;reproductive cells; sexual reproduction by means of the conjugation of similar gametes or by the fertilisation of a typicalnbsp;egg-cell by a motile spermatozoid.

This family of algae is represented at the present day by numerous and widely distributed marine and fresh-waternbsp;genera, as well as by genera growing in moist air or asnbsp;endophytes in the tissues of higher plantsh

Seeing how very few fossil forms have been described which have any claim to inclusion in this subdivision of the Algae,nbsp;it is unnecessary to enumerate or define the various familiesnbsp;of the Chlorophyceae. It is true that many species have beennbsp;figured as examples of different genera of green algae, but fewnbsp;of these possess any scientific value. There is, however, onenbsp;division of the Chlorophyceae, the Siphoneae, which must benbsp;treated at some length on account of its importance from anbsp;palaeobotanical and geological point of view.

� The Chlorophyceae have recently been exhaustively dealt with by Wille (97) in Engler and Prantl�s Pflanzenfamilien.

Thallus consisting of simple or branched cells very rarely divided by septa, and containing many nuclei. In certainnbsp;genera the branches form a pseudoparenchymatous tissue bynbsp;their repeated branching, and as a result of the intimate feltingnbsp;together of the branched cells. Reproduction is effected eithernbsp;by the conjugation of similar gametes or by the fertilisationnbsp;of an egg-cell.

Vaucheria and Botrydium are two well-known British genera of this order, but most of the recent representatives livenbsp;in tropical and sub-tropical seas. The most striking characteristic feature of this division of the Ghlorophyceae is the factnbsp;that the thallus of a siphoneous alga consists of an unseptatenbsp;coenocyte; the plant may be extremely small and simple, or itnbsp;may reach a length of several inches, but in all cases the bodynbsp;does not consist of more than one cell or coenocyte.

From a palaeontological standpoint the Siphoneae are of exceptional interest. It is impossible to do more than refernbsp;to a few of the living and fossil genera. There are numerousnbsp;fossil representatives already known, and there can be littlenbsp;doubt that further research would be productive of valuablenbsp;results.

As examples of the order, a few genera may be described belonging to the three families Caulerpaceae, Codiaceae, andnbsp;Dasycladaceae.

Thallus unseptate, showing an extraordinary variation in the external differentiation of the plant-body. Reproduction isnbsp;effected by means of detached portions of the parent plant.

The genus Caulerpa, represented by a few species in the Mediterranean and by many tropical forms, has already beennbsp;alluded to as a striking example of a plant which appearsnbsp;under a great many different forms*. As a recent writernbsp;has said, �Nature seems to have shown in this genus thenbsp;utmost possibilities of the siphoneous thallusl� Fragments ofnbsp;^ Vide p. 142.nbsp;nbsp;nbsp;nbsp;^ Murray G. (95) p. 123.

coniferous twigs, the tracks and burrows of various animals and other objects have been described by several authors as fossilnbsp;species of Caitlerpa. As an illustration of the identification of anbsp;very doubtful fossil as a species of Caulerpites, reference may benbsp;made to such a form as 0. cactoides G�ppd from Silurian andnbsp;Cambrian rocks. There are several examples of this fossilnbsp;in the Brussels Museum which probably owe their origin tonbsp;some burrowing animal, and may be compared with Zeiller�snbsp;figures of the tunnels made by the mole-cricket (fig. 30, 4)^.

Mr Murray, of the British Museum, has recently described what he regards as a trustworthy example of a fossil Gaulerpanbsp;from the Kimeridge Clay near Weymouthl Specimens of thenbsp;fossil were first figured in a book on the geology of the Dorsetnbsp;coast as casts of an equisetaceous plant

To this fossil Murray has assigned the name Gaulerpa Garruthersi, and given to it a scientific diagnosis. The bestnbsp;specimens have the form of a slender central axis, giving offnbsp;at fairly regular intervals whorls of short and somewhat clavatenbsp;branches; they bear a superficial resemblance to such anbsp;recent species as Gaulerpa cactoides Ag. An examination ofnbsp;several examples of this fossil leads me to express the opinionnbsp;that there is not sufficient reason for assigning to them thenbsp;name of a recent genus of algae ^ To use the generic name ofnbsp;a recent plant without following the common custom of addingnbsp;on the termination � ites � (i.e. Gaiderpites) is as a general rulenbsp;to be avoided in dealing with fossil forms; and there are,nbsp;I believe, no satisfactory grounds for referring to these fossilsnbsp;as trustworthy examples of a Mesozoic alga.

In the present case I am disposed to regard the Gaulerpa-like casts as of animal rather than plant origin. The clavate branches have the form of very deep moulds in the hard brownnbsp;rock which have been filled in with blue mud. It is hardlynbsp;conceivable that the branches of a soft watery plant such asnbsp;Gaulerpa could leave more than a faint impression on an old seafloor. The specimens occur in different positions in the matrix

3 Murray G. (92) p. 11; also (95) p. 127. �* Damon (88) PI. xix. fig. 12.nbsp;nbsp;nbsp;nbsp;� Vide also Bothpletz (96) p. 894.

of the rock and they are not confined to the lines of bedding; in none of the examples is there any trace of carbonaceous matternbsp;in association with the deep moulds. On the whole, then, thisnbsp;Kimeridge fossil cannot, I believe, be accepted as an authenticnbsp;example of a Mesozoic Caulerpa.

It is not improbable that some of the supposed fossil algae may be casts of egg-cases or spawn-clusters of animals. Innbsp;Ellis� Natural History of the Corallines' there is a drawingnbsp;representing a number of disc-like ovaries attached to a toughnbsp;ligament, and referred to the mollusc Bvccinum, which bears anbsp;certain resemblance to the Weymouth fossil. A similar bodynbsp;is figured by Fuchs^ in an important memoir on supposed fossilnbsp;algae.

It is not suggested that the Caulerpa Carruthersi of Murray should be regarded as the cast of some molluscannbsp;egg-case attached to a slender axis, but it is important to bearnbsp;in mind the possibility of matching such extremely doubtfulnbsp;fossils with other organic bodies than the thallus of a Caulerpa.nbsp;In an example of an egg-case in the Cambridge Zoologicalnbsp;Museum, referred to a species of Pyrula, there is a hard, longnbsp;and slender axis, bearing a series of semicircular chambers dividednbsp;into radial compartments. The whole is hard and horny andnbsp;might well be preserved as a fossil.

The members of this Order present a considerable diversity of form as regards the shape of the plant-body; the thallus ofnbsp;some species is encrusted with carbonate of lime. The ordernbsp;is widely distributed in tropical and temperate seas.

Among the recent genera Penicillus and Codiurn may be chosen as important types from the point of view of fossilnbsp;representatives. ,

The thallus of Codiurn consists of a spongy mass of tubular cell-branches which are differentiated into two fairly distinctnbsp;regions, an outer peripheral layer in which the branches havenbsp;' Ellis (1755) PI. XXXIII. a p. 86.nbsp;nbsp;nbsp;nbsp;^ Fuchs (95) PI. viii. fig. 3.

long club-shaped terminations, and an inner region consisting of loosely interwoven filaments.

Codium Bursa L. and G. tomentosum Huds. are two well-known British species, the former presents the appearance of a spongynbsp;ball of cells, and in the latter the thallus is divided up intonbsp;dichotomously forked branches^ In this genus the thallusnbsp;is not encrusted with carbonate of lime, at least in recentnbsp;species.

Bothpletz^ instituted this genus for certain small spherical or oval bodies varying from 1 mm. to 2 cm. in diameter, whichnbsp;have been found on crinoid stems or shell fragments of Triassicnbsp;age. Each spherical body consists of dichotomously branchednbsp;single-celled filaments, between 50 and 100/a in breadth, andnbsp;from 300�500/u, in height. The tubular cavities occasionallynbsp;swell out into spherical spaces which are regarded by Eothpletznbsp;as sporangia.

There is not sufficient evidence that Sphaerocodium Bor-nemanni Roth, has been correctly referred to the Codiaceae. The sporangia-like swellings described by the author of thenbsp;species are not by any means conclusive as characters ofnbsp;important taxonomic value. Figure 37, D, illustrates thenbsp;general stnicture of the fossil as seen in a transverse sectionnbsp;of one of the calcareous grains.

Like Girvanella, which has been referred by some writers to the Siphoneae, Sphaerocodium occurs in the form of ooliticnbsp;grains. In the Triassic Eaibler and St Cassian beds of thenbsp;Tyrol, as well as in rocks of Rhaetic age in the Eastern Alps, itnbsp;makes up large masses of limestone. Eothpletz compares thenbsp;structure of this genus with that of the recent alga Codiumnbsp;adhaere7is Ag., but it is wiser to regard such tubular structuresnbsp;as Girvanella, Siphonema^ and Sphaerocodium as closely alliednbsp;organisms, which are probably algae, but too imperfectly knownnbsp;to be referred to any particular family.

The recent genus Penicillus is one of those algae formerly included among animals. Fig. 33, O, has been copied from anbsp;drawing of a species of Penicillus given by Lamouroux^ undernbsp;the generic name of Nesea in his treatise on the genera ofnbsp;Polyps published in 1821. He describes the genus as a brushlike Polyp with a simple stem.

The thallus consists of a stout stem terminating in a brush-like tuft of fine dichotomously-branched filaments. Thenbsp;apical branches are divided by regular constrictions into shortnbsp;oval or rod-like segments which may be encrusted with carbonate of lime. A few of the segments from the terminal tuftnbsp;of a recent Penicillus are showm in fig. 35, E. Each of thesenbsp;calcareous segments has the form of an oval shell perforated atnbsp;each end, and the wall is pierced by numerous fine canals.nbsp;Penicillus is represented by about 10 recent species, which withnbsp;one exception live in tropical seas.

The recognition of Penicillus, or a very similar type, in a fossil condition is due to Munier-Chalmasl This keen observernbsp;has rendered great service to palaeobotany by directing attentionnbsp;to the calcareous algae in the Paris basin beds, and by provingnbsp;that many of the fossils from these Tertiary deposits havenbsp;been erroneously included by previous writers among thenbsp;Foraminiferah It is greatly to be desired that Prof Munier-Chalmas may soon publish a monograph on the fossil Siphoneousnbsp;forms of which he possesses a unique collection.

In his Natural History of Invertebrate Animals, Lamarck described some small oval bodies from the Calcaire Grossiernbsp;(Eocene) of the Paris basin under the name of Ovulites. He

� For references to genera of calcareous algae previously referred to Foraminifera, vide Sherborn (93).

Fig. 33. A and B, Cymopolia harhata (L.); A, transverse section of the calcareous cylinder. B, verticillate branches and sporangium after removal of the calcareous matrix (Anbsp;and B after Munier-Ohalmas). C and D, Acicularia Andrussowi Solms (C, after Andrus-sowi; B, after Solms). E, Acicularia Mioceuica Beuss; section of a spicula (after Beuss).nbsp;F and G, Acicularia sp. (after Carpenter), Fx40; Gx20. H, Acicularia Schencki (Mob.)nbsp;(after Solms). I, Acetdbularia Mediterranea Lamx.; section of the cap (after Falkenberg).nbsp;K and L, Ovulites margariiula (Lam.) (after Munier-Chalmas); K slightly enlarged; L, anbsp;piece of the thallus more highly magnified. M, Corallina harhata (L.) (after Ellis, nat. size).nbsp;N, C. harhata (L.); the surface of the thallus; magnified. 0,Penicillu$ pyramidalis (Lamx.)nbsp;(after Lamouroux, nat. size).

defined them as follows :�� Polypier pierreux, libre, ovuliforme ou cylindrac�, crenx int�rieurement, souvent perc� aux deuxnbsp;bouts. Pores tres petits, r�guli�rement dispos�s a la surface*.�

The specimens are referred to two species, Ovulites mar-garitula and 0. elongata.

By some subsequent writers'* these calcareous fossils, like miniature birds� eggs with a hole at either end, were includednbsp;among the Zoophytes. Carpenter and others afterwards referrednbsp;Ovulites to the Foraminifera, and compared the genus withnbsp;Lagena^. The single specimens of Ovulites have a length ofnbsp;2�6 mm. At each end there is usually a fairly large andnbsp;somewhat irregular hole (fig. 35, F), and in some rarer casesnbsp;there may he two apertures at the broader end of an Ovulite.nbsp;A good example of Ovulites margaritula with two pores at thenbsp;broader end is figured by Michelinf The surface of the shellnbsp;when seen under a low magnifying power appears to be coverednbsp;over with regularly arranged circular pores, which are thenbsp;external openings of fine canals (fig. 33, L).

In 1878 Munier-Chalmas expressed the opinion, which was supported by strong evidence, that Ovulites should he referrednbsp;to the siphoneous algae�. He regarded it as genericallynbsp;identical with Penicillus {Coralliodendron, Kiitzing). It hasnbsp;already been pointed out that in Penicillus the apical tuft ofnbsp;filaments is partially calcareous (fig. 33, 0)�. The individualnbsp;calcareous segments agree almost exactly with the fossil Ovulites.nbsp;Asa rule the Ovulites occur as separate egg- or rod-like bodies,nbsp;but Munier-Chalmas informs me that occasionally two or threenbsp;have been found joined end to end in their natural position.nbsp;The terminal holes in the fossil specimens represent thenbsp;apertures left after the detachment of the calcareous segmentsnbsp;from the uncalcified filaments 'of the alga. The segmentsnbsp;with two holes at the broader end were no doubt situated atnbsp;the base of dichotomising branches as shown in fig. 33, K.

The restoration of Ovulites, shown in fig. 33, K, bears a striking resemblance to the figure of an Australian Penicillus given bynbsp;Harvey in his Phycologia Aiistralica'^.

It is probable that these Eocene forms agreed closely in habit with the recent species of Penicillus. The portionsnbsp;preserved as fossils are segments of the filaments whichnbsp;probably formed a terminal brush of fine branches supportednbsp;on a stem. The retention of the original generic name Ovulitesnbsp;is on the whole better than the inclusion of the fossil species innbsp;the recent genus. The Tertiary species lived in warm seas ofnbsp;the Lower and Middle Eocene of England, Belgium, France andnbsp;Italy.

An example of an Eocene species of Halimeda has been recorded by Fuchs from Greifenstein under the name ofnbsp;Halimeda Saportae^. The impression has the form of anbsp;branched plant consisting of wedge-shaped or oval segments,nbsp;and there is a close resemblance to the thallus of a recentnbsp;Halimeda, e.g. H. gracilis Harv. It is not improbable thatnbsp;Fuchs� determination is correct, but without more definitenbsp;evidence than is afforded by a mere impression it is a littlenbsp;rash to make use of the recent generic name.

In this family of Siphoneae are included a number of genera represented by species living in tropical and subtropicalnbsp;seas.

The thallus consists of an elongated axial cell fixed to the substratum by basal rhizoids, and bearing whorls of lateralnbsp;appendages of limited growth which may be either simple ornbsp;branched. Many of the lateral branches bear sporangia ornbsp;spores. The thallus is in many species encrusted with carbonate of lime.

The two genera Acetahularia and Gymopolia may be briefly described as recent types which are represented by trustworthynbsp;fossil forms.

With the exception of A. mediterranea Lamx. (fig. 34) the few living species of this genus are confined to tropical seas.

The habit of Acetahularia is well illustrated by the photograph of a cluster of plants of A. mediterranea Lamx.^ reproduced

* Lamouroux gives a figure of Acetahularia, and includes this genus with several other algae in the animal kingdom (Lamouroux [21] p. 19, PI. nxix.).

in fig. 34. Th� thallus consists of a delicate stalk attached to the substratum by a tuft of basal holdfasts, and expanded distally intonbsp;a small circular disc 10�12 mm. in diameter and more or lessnbsp;concave above. This terminal cap is made up of a number ofnbsp;laterally fused appendages given off from the upper part of thenbsp;stalk in the form of a crowded whorl. The whole thallus resembles a small and long-stalked calcareous fungus. In each radiallynbsp;elongated compartment of the fertile cap (fig. 33,1) there arenbsp;several sporangia (gametangia) developed; these eventuallynbsp;open and produce numerous ciliated gametes which give rise tonbsp;zygospores by conjugation. Fig. 33, I, represents the cap of annbsp;Acetabularia in radial section and surface-view; the two radialnbsp;compartments seen in section contain the elliptical gametangia;nbsp;the circular markings at the base of the figure are scars ofnbsp;sterile deciduous branches.

The whole plant is unicellular, each chamber in the disc being in open communication with the stem of the plant.

In a recent monograph on the Acetabularieae, Solms-Laubach* has described a new type of these algae which is of specialnbsp;importance from the point of view of the past history of thenbsp;family. Mobius described an example of Acetabularia in 1889nbsp;under the name A. Schencki; this species has since beennbsp;placed in D�Archiac�s genus Acicularia'^ Acicularia Schencki^nbsp;bears a close resemblance as regards external form to Acetabularia mediterranea. In the latter species the walls of thenbsp;terminal disc compartments are calcified, and the cavity of eachnbsp;of the laterally fused members contains numerous free spores;nbsp;in Acicularia, the cavity of each disc-ray is occupied by a calcareous substance in the form of a spicule containing numerousnbsp;cavities in each of which is a single sporangium. A singlenbsp;spicule is seen in fig. 33, H, showing the sphei�ical pockets innbsp;which the sporangia were originally situated. This species.

1 Solms-Laubach (95'9. nbsp;nbsp;nbsp;^ D�Archiae (43) p. 386, PI. xxv. fig. 8.

Acicularia Schencki, has been recorded from Martinique, Guadeloupe, Brazil, and a few other places.

The genus Acicularia was founded by D�Archiac for certain minute calcareous spicules found in the Eocene sands (Calcairenbsp;Grossier) of the Paris basin. D�Archiac describes one species,nbsp;Acicularia, pavantina, which he defines as follows :�� Polypiernbsp;aciculaire, �largi, et l�g�rement comprim� a sa partie sup�rieure,nbsp;qui est �chancr�e au milieu. Surface couverte de petits poresnbsp;simples, nomhreux, dispos�s irr�guli�rementh� The same speciesnbsp;is figured also in Michelin�s Iconographie Zoophytologique, andnbsp;described as an organism of which the exact zoological positionnbsp;is uncertain^. After these fossils had been placed in variousnbsp;divisions of the animal kingdom, Carpenter� described severalnbsp;specimens as portions of foraminifera. Finally, Munier-Chalmasnbsp;removed Acicularia to the plant kingdom, and �with rarenbsp;divination � placed the genus among the Acetahularieae. Thenbsp;history of our knowledge of the true nature of Acicularianbsp;is of unusual interest. Some of the specimens of this genusnbsp;figured in Carpenter�s monograph have the form of imperfectnbsp;long and narrow bodies tapering to a point at one end and broadnbsp;at the other (fig. 33, F and G); they are joined together laterallynbsp;and pitted with numerous small cavities. From the resemblancenbsp;of such specimens to a fragment of the terminal fertile disc of thenbsp;recent Acetabularias, Munier-Chalmas referred the fossils to thisnbsp;type of algae. In the living species which were then knownnbsp;the radiating chambers of the disc contained loose sporangia,nbsp;without any calcareous matrix filling the cavity of the chambers.nbsp;In the fossil Acicularias, on the other hand, the manner ofnbsp;preservation of the pitted calcareous spicules pointed to thenbsp;occurrence of sporangia embedded in cavities in a calcareousnbsp;matrix. Subsequent to Munier-Chalmas� somewhat daringnbsp;conclusions as to the relation of Acicularia to Acetahularia,nbsp;Solms-Laubach found that the species originally described bynbsp;M�bius as Acetahularia Schencki from Guadeloupe pre.sentednbsp;exactly those characters in which the fossil specimens differ

from Acetabularia. The genus Acicularia formerly restricted to fossil species is now applied also to this single living speciesnbsp;Acicularia Schencki.

� Discus fertilis terminalis e radiis inter se conjunctis formatus, coronis et inferiore et superiors praeditis, sporae massa mucosa calce incrustatanbsp;coalitae, pro radio spiculam solidam cuneatam formantes^.�

As Solms-Laubach points out in his recent monograph, Munier-Chalmas� conjecture, �which had little to support itnbsp;in the fossil material, has been more recently proved true innbsp;the most brilliant fashion by the discovery of a living speciesnbsp;of this genus.�

species was first described by Andrussow� as Acetabularia miocenica from the Crimea. It occurs in Miocene rocks southnbsp;of Sevastopol, and, with Ostrea and Pecten, forms masses ofnbsp;white limestone.

In each sporangial ray of the disc the cavity contains a calcareous spicula bearing spore cavities in four rows. �Roundnbsp;each spore-cavity there is a circular zone which stands out,nbsp;when viewed in reflected light, through its white colour againstnbsp;the central mass of the spicule, though a sharp contour is notnbsp;visible^.� Fig. 33, C, is taken from a somewhat diagrammaticnbsp;sketch by Andrussow; it shows ten of the fertile rays ofnbsp;the disc. The thick walls of the chambers are seen in the twonbsp;lowest rays, and in the next two rays the spore-cavities arenbsp;represented. A more accurate drawing, from Solms-Laubach�snbsp;memoir, is reproduced in fig. 33, D. The calcareous spiculenbsp;wdth numerous spore-cavities shown in fig. 33, H, is from anbsp;fertile ray of the recent species Acicularia Schencki. Thisnbsp;corresponds to the spore-containing calcareous matrix in eachnbsp;ray of the disc of Acicidaria Andrussowi Solms. The spiculenbsp;copied in fig. 33, F from one of Carpenter�s drawings� of an

Eocene specimen bears the closest resemblance to the recent spicule of fig. 33, H, and emphasizes the very close relationshipnbsp;between the fossil forms and the single rare tropical species.

2. Acicularia miocenica Keuss. Another Tertiary species has been described under this name by Reuss^ from the Miocenenbsp;of the Vienna di.strict, from the Leithakalk of Moravia andnbsp;elsewhere. It agrees very closely with the recent species A.nbsp;Schenckii. A section of one of the spicules of this species isnbsp;shown in fig. 33, E; the dark patches represent the pocketsnbsp;in the calcareous spicule which were originally occupied bynbsp;sporangia and spores.

The genus Cymopolia is at present represented by two species, C. barbata (L.) and C. viexicana, Ag., living in thenbsp;Gulf of Mexico and off the Canary Islands.

Cymopolia and Acetabularia, with several other calcareous algae, are figured by Ellis and other writers as members of thenbsp;animal kingdom. Ellis speaks of the species of Cymopolianbsp;which he figures as the Rosary Bead-Coralline of Jamaica.

Fig. 33, M, has been drawn from a figure published by Ellis in his Natural History of the Corallines published in llSfi'quot;. Thenbsp;thallus has the form of a repeatedly forked body, of which thenbsp;branches are divided into cylindrical joints thickly encrustednbsp;with carbonate of lime, but constricted and uncalcified at thenbsp;limits of each segment. A tuft of hairs is given off from thenbsp;terminal segment of each branch. The axis of each branch ofnbsp;the thallus is occupied by a cylindrical and unseptate cell whichnbsp;gives off crowded whorls of lateral branches. In the lower partnbsp;of fig. 33, M, the calcareous investment has been removed, andnbsp;the branches are seen as fine hair-like appendages of the centralnbsp;cell. The branches given off from the constricted portions ofnbsp;the axis are unbranched simple appendages, but the othersnbsp;terminate in bladder-like swellings, each of which bears an apicalnbsp;Sporangium. The sporangia are surrounded and enclosed bynbsp;the swollen tips of four to six branches which spring from thenbsp;summit of the sporangial branch. Fig. 33, A, represents partnbsp;1 Eeuss (61) p. 8, figs. 5-8.nbsp;nbsp;nbsp;nbsp;^ Ellis (1755) PI. xxv. C.

of a transverse section through the calcareous outer portion of a branch of Cymopolia-, the darker portions or cavities innbsp;the calcareous matrix were originally occupied by the lateralnbsp;branches and sporangia*.

In Fig. 33, B, the sporangial branch with the terminal sporangium and three of the investing branches are morenbsp;clearly shown, the surrounding calcareous investment and thenbsp;thallus having been removed by the action of an acid.

In a transverse section of a branch from which the organic matter had been removed, and only the calcareous matrix left,nbsp;one would see a central circular cavity surrounded by a thicknbsp;calcareous wall perforated by radially disposed canals and containing globular cavities; the canals and cavities being occupiednbsp;in the living plant by branches and sporangia respectively.

The two circular cavities shown in the figure mark the position of the sporangia which are borne on branches withnbsp;somewhat swollen tips. From the summit the left-handnbsp;sporangial branch shown in fig. S3, A, three of the secondarynbsp;branches are represented by channels in the calcareous matrix ;nbsp;the two black dots on the face of the sporangiaphore being thenbsp;scars of the remaining two secondary branches.

By the lateral contact of the swollenquot; ends of the ultimate branches enclosing the sporangia the whole surface of thenbsp;thallus, when examined with a lens, presents a pitted appearance.nbsp;Each pit or circular depression (fig. 33, N) marks the positionnbsp;of the swollen tip of a branch.

This form of thallus represents a type which is met with in several members of the Dasycladaceae. It would carry usnbsp;beyond the limits of a short account to describe additionalnbsp;recent genera which throw light on the numerous fossil species.nbsp;For further information as to the recent members of the family,nbsp;the student should refer to Murray�s Seaweeds^, and for a morenbsp;detailed memoir on the group to Wille�s recent contribution tonbsp;the Pflanzenfamilien^ of Engler and Prantl. Among the variousnbsp;special contributions to our knowledge of the Dasycladaceae,

^ Solms-Laubaoh (91) p. 38 gives a detailed description with two figures of a recent species of Cymopolia.

those by Munier-Chalmash Cramer'�j Solms-Laubach�, and Church^, may be mentioned.

The publication of a short preliminary note by Prof. Munier-Chalmas in the Comptes Rendiis for 1877 was the means of calling attention to the exceptional importance of the calcareousnbsp;Siphoneae as algae possessing an interesting past history, ofnbsp;which satisfactory records had been preserved in rocks of variousnbsp;ages. Decaisne had pointed out in 1842 that certain marinenbsp;organisms previously regarded as animals should be transferrednbsp;to the plant kingdom. Such seaweeds as Halimeda, Udotea,nbsp;Penicillus and others were thus assigned to their correctnbsp;position. Many fossil algae belonging to this group continuednbsp;to be dealt w'ith as Foraminifera until Munier-Chalmas demonstrated their true affinities. In Gtimbel�s monograph on thenbsp;so-called Nullipores found in limestone rocks, published in 1871�,nbsp;several examples of siphoneous algae are included among thenbsp;fossil Protozoa.

In recent years there have been several additions to an already long list of fossil Siphoneae. In addition to thenbsp;niimerous and well-preserved specimens, representing a largenbsp;number of generic and specific forms, which have been collectednbsp;from the Eocene of the Paris basin, there is plenty of evidencenbsp;of the abundance of the members of the Dasycladaceae in thenbsp;Triassic seas. In the Triassic limestones of the Tyrol, as wellnbsp;as in other regions, the calcareous bodies of siphoneous algaenbsp;have played no inconsiderable part as agents of rock-building�.nbsp;Genera have been recorded from Silurian and other Palaeozoic horizons, and there is no doubt that the Verticillatenbsp;Siphoneae of to-day are the remnants of an extremely ancientnbsp;family, which in former periods was represented by a much morenbsp;widely distributed and more varied assemblage of species.nbsp;There is probably no more promising field of work in thenbsp;domain of fossil algae than the further investigation of thenbsp;numerous forms included in Munier-Chalmas� class of Siphoneae

Verticillatae. A brief description of a few genera from different geological horizons must suffice to draw attention to thenbsp;character of the data for a phylogenetic history of this group.

The fossil examples of the genus Gymopolia {Polytrypa) were originally described by Defrance* in the Dictionnaire desnbsp;Sciences Naturelles as small polyps under the generic namenbsp;Polytrypa.

In the Eocene sands of the Paris basin there have been found numerous specimens of short, calcareous tubes whichnbsp;Munier-Chalmas has shewn are no doubt the isolated segmentsnbsp;of an alga practically identical with the recent Gymopolia. Anbsp;section^ through one of the fossil segments presents preciselynbsp;the same features as those which are represented in fig. 33, A.nbsp;The habit of the Eocene alga and its minute structure werenbsp;apparently almost identical with those of the recent species,nbsp;Gymopolia barbata. The two drawings of Gymopolia reproducednbsp;in fig. 33, A and B, have been copied from Munier-Chalmas�nbsp;note in the Gomptes Pendus^; the corresponding figures givennbsp;by this author of the Eocene species {Gymopolia elmigata Deb.)nbsp;are practically identical with figs. A and B, and show nonbsp;points of real difference. The segments of the thallus of thenbsp;fossil species, as figured by Defrance**, appear to be rathernbsp;longer than those of the recent species. The calcareousnbsp;investment of the axial cell of the thallus was traversed bynbsp;regular verticils of branches or �leaves�; the central branchnbsp;of each whorl terminates in an oval sporangial cavity, exactlynbsp;as in fig. 33, A and B; and from the top of this branch therenbsp;is given off a ring of slender prolongations which terminatenbsp;on the surface of the calcareous tube as regularly disposednbsp;depressions, which were no doubt originally occupied by theirnbsp;swollen distal ends as in the recent species.

This generic name was proposed by Stolley for certain branched and curved tubes found in Silurian boulders from the

North German drift'. The tubes have a diameter of '�1 mm., and are perforated by radial canals which probably mark thenbsp;position of verticils of branches given off at right angles to thenbsp;central axis. The surface of the tubes is divided into regularnbsp;hexagonal areas.

The resemblance of these Silurian fossils to Diplopora and other genera favours their inclusion in the Verticillatenbsp;Siphoneae.

The fossils included in this genus were first described by Sandberger from the middle Devonian rocks of the Eifel, andnbsp;referred by him to the animal kingdom. More recently Deeckenbsp;has suggested the removal of the genus to the calcareousnbsp;Siphoneae, and such a view appears perfectly reasonable,nbsp;although without more data it is not possible to speak withnbsp;absolute certainty.

Sycidium melo. (Sandb.) Fig. 32, B. The specimen represented in fig. 32, B (i), (ii), drawn from Deecke�s figures^ has the form of a small oval calcareous body, 1 mm. in transversenbsp;diameter and 1�1'3 mm. in longitudinal diameter. It is pointednbsp;at one end and flattened at the other. At the flatter end therenbsp;is a circular depression, continued into a funnel-shaped cavity,nbsp;and on the walls of this cavity there are 18�20 radially disposednbsp;ribs, which extend over the surface of the whole body. A seriesnbsp;of ti'ansverse ribs intersects the vertical ribs at right angles.nbsp;The calcareous wall is perforated by numerous whorls of circularnbsp;pores, and the internal cavity is a simple undivided space. Eachnbsp;of these oval bodies (fig. 33, B) is probably the segment of anbsp;thallus, and the perforations in the wall may have been originallynbsp;occupied by lateral prolongations from the unseptate axial cellnbsp;of the thallus. Sycidium bears a fairly close resemblance to thenbsp;Tertiary Ovulites.

This genus of algae is characteristic of Triassic rocks, and is especially abundant in Muschelkalk and Lower Keuper limestones of the Alps, Silesia, and elsewhere. The thallus, ornbsp;rather the calcareous portion of the thallus, has the form of anbsp;thick-walled tube, with a diameter of about 4 mm., andnbsp;occasionally reaching a length of 50 mm. At one end thenbsp;tube has a rounded and closed termination, and the wall isnbsp;pierced throughout its whole length by regular whorls of finenbsp;canals. Diplopora agrees with Cymopolia in its main features.

Fig. 35, A. affords a diagrammatic view of a Diplopora tube, and shews the arrangement of the numerous whorls of canals.nbsp;In fig. 35, B, a piece of limestone is represented containingnbsp;several Diplopora.s cut across transversely and more or less

Fig. 35. A, B, Diplopora. x 2. C, D, G�/roporeHa (after Benecke. x4). E, Calcareous segments of Fenicillus, from a specimen in the British Museum. X 5. F, a single segment of Oculites margaritiila Lam. x 4. G, Confervitesnbsp;chantransioides Born, (after Bornemann. x 160).

obliquely. In an obliquely transverse section of a tube perforated by horizontal canals the cavities of the canals necessarily appear as holes or discontinuous canals in the substance of thenbsp;calcareous wall. The manner of occurrence of the specimensnbsp;points to the abundance of this genus in the Triassic seas, andnbsp;suggests that the calcareous tubes of Diplopora may have beennbsp;important factors in the building up of limestone sedimentshnbsp;In many instances no doubt the carbonate of lime of the thallusnbsp;has been dissolved and recrystallised, and the original formnbsp;completely obliterated. As in the rocks built up largely ofnbsp;calcareous Florideae (p. 185) which have lost their structure,nbsp;it is a legitimate inference that some of the limestone rocksnbsp;which shew no trace of organic structure may have been innbsp;part derived from the calcareous incrustation of various algalnbsp;genera.

In this genus from the Alpine Trias the structure of the calcareous tube is very similar to that in Diplopora, but innbsp;Gyroporella the canals form less distinct whorls and are closednbsp;externally by a small plate, as seen in figs. 35, C and D.

As Solms-Laubach has pointed out, the branch-systems of Diplopora, Gyroporella and other older genera are muchnbsp;simpler than in the Tertiary genera Dactylopora and others^

A species of �yroporella, G. hellerophontis, has recently been described by Rothpletz'� from Permian rocks in thenbsp;Southern Tyrol. The thallus is tubular in form and has anbsp;diameter of �5�1 mm.

The genus Dactylopora was founded by Lamarck^ on some fossil specimens from the Calcaire Grossier and included amongnbsp;the Zoophytes. D�Orbigny afterwards included it among thenbsp;Foraminifera, and the structure of the calcareous body has beennbsp;described by Carpenter^ and other writers on the Foraminifera.

In a specimen of Dactylopora cylindracea Lam. from the Paris basin, for which I am indebted to Munier-Chalmas, the tubularnbsp;thallus measures 4 mm. in diameter; at the complete end it isnbsp;closed and bluntly rounded. The wall of the tube is perforated bynbsp;numerous canals, and contains oval cavities which were no doubtnbsp;originally occupied by sporangia. The shape of the specimensnbsp;is similar to that of Diplopora, but the canals and cavitiesnbsp;present a characteristic and more complex appearance, whennbsp;seen in a transverse section of the wall, than in the older genusnbsp;Diplopora. G�mbel has given a detailed account of thisnbsp;Tertiary genus in his memoir on Die sogenannten Nulliporerd ]nbsp;he distinguishes between Dactyloporella and Gyroporella bynbsp;the existence of cavities in the calcareous wall of the tube innbsp;the former genus, and by their absence in the latter. The ovalnbsp;cavities in a Dactyloporella were originally occupied bynbsp;sporangia; in Diplopora and Gyroporella the sporangia werenbsp;probably borne externally and on an uncalcified portion of thenbsp;thallus.

In addition to the few examples of fossil species described above there are numerous others of considerable interest, whichnbsp;illustrate the great wealth of form among the Tertiary andnbsp;other representatives of the Verticillate Siphoneae.

Reference has already been made to Vermiporella as an example of a Silurian genus. Other genera have been describednbsp;by Stolley from Silurian boulders in the North-German driftnbsp;under the names Palaeoporella, Dasyporella and Rhabdoporella^;nbsp;the latter genus is compared with the Triassic Diplopora, andnbsp;the two preceding with the recent Bornetella.

Schl�ter has transferred a supposed Devonian Foraminiferal genus, Coelotrochium^, to the list of Palaeozoic Siphoneae.nbsp;Munier-Chalmas regards some of the fossils described ' bynbsp;Saporta under the name of Goniolina*, and classed among thenbsp;inflorescences of pro-angiospermous plants, as examples of Jurassicnbsp;Siphoneae. The shape and surface-features of some of the

� Stolley (93). nbsp;nbsp;nbsp;^ Schl�ter (79).nbsp;nbsp;nbsp;nbsp;^ Saporta (91) PI. xxxii. amp;o.

examples of Goniolina suggest a comparison with Echinoid spines, but the resemblance which many of the forms in thenbsp;Sorbonne collection present to large calcareous Siphoneae isnbsp;still more striking. A comparison of Saporta�s fig. 5, PL xxxiii.nbsp;and fig. 4, PI. xxxii. in volume iv. of the Floi'e Jurassique, withnbsp;the figures given by Solms-Laubach' and Cramerof speciesnbsp;of Bornetella brings out a close similarity between Goniolinanbsp;and recent algae; the chief difference being the greater size ofnbsp;the fossil forms. The possibility of confounding Echinoidnbsp;spines with calcareous Siphoneae is illustrated by Rothpletz*,nbsp;who has expressed the opinion that Glimbel�s Haploporellanbsp;fasciculata is not an alga but the spine of a sea-urchin.

Among Cretaceous forms, in addition to Goniolina, which passes upwards from Jurassic rocks, Triploporella^ and othernbsp;genera have been recorded.

Uteria^ is an interesting type of Tertiary genera; it occurs in the form of barrel-shaped rings, which are probably thenbsp;detached segments of a form in which the central axial cellnbsp;was encrusted with carbonate of lime, but the sporangia andnbsp;the whorls of branches differed from those of Gymopolia innbsp;being without a calcareous investment.

Without attempting to describe at length the fossil forms referred to this division of the Chlorophyceae, there is one fossilnbsp;which deserves a passing notice. Brongniart in 1828� institutednbsp;the generic term Confervites for filamentous fossils resemblingnbsp;recent species of confervoid algae. Numerous fossils havenbsp;been referred to this genus by different authors, but theynbsp;are for the most part valueless and need not be furthernbsp;considered. In 1887 Bornemann described some new formsnbsp;which he referred to this genus from the Cambrian rocks ofnbsp;Sardinia. He describes the red marble of San Pietra, near

2 Solms-Laubach (91), p. 40. fig. 3. Vide also Deecke (83) PL i. fig. 12. * Brongniart (28) p. 211.

Masne, as being in places full of the delicate remains of algae having the form of branched filaments, and appearing in sectionsnbsp;of the rock as white lines on a dark crystalline matrix. Innbsp;fig. 35, G, one of these Sardinian specimens is represented. Thisnbsp;form is named Cmfervites Chantransioides^; the thallus consistsnbsp;of branched cell-filaments, having a breadth of 6�T/x, andnbsp;composed of ovate cells. It is possible that this is a fragmentnbsp;of a Cambrian alga, but the figures and descriptions do notnbsp;afford by any means convincing evidence. From post-Tertiarynbsp;beds various genera, such as Vaucheria and others, have beennbsp;recorded, but they possess but little botanical value.

During the last few years much has been written by two-French authors. Dr Renault and Prof. Bertrand, on the subject of the so-called Boghead of France, Scotland, and othernbsp;countries. They hold the view that the formation of thenbsp;extensive beds of this carbonaceous material was due to thenbsp;accumulation and preservation of enormous numbers of minutenbsp;algae which lived in Permo-Carboniferous lakes.

In an article contributed to Science-Progress in 1895 I ventured to express doubts as to the correctness of the conclusions of MM. Renault and Bertrand^. Since then Prof.nbsp;Bertrand has very kindly demonstrated to me many of hisnbsp;microscopic preparations of various Bogheads, and I am indebted to Prof. Bayley Balfour of Edinburgh for an opportunitynbsp;of examining a series of sections of the Scotch Boghead. Thenbsp;examination of these specimens has convinced me of thenbsp;difficulties of the problems which many investigators have triednbsp;to solve, but it has by no means led me to entirely adopt thenbsp;views expressed by MM. Bertrand and Renault.

The Boghead or Torbanite of Scotland was rendered famous by a protracted lawsuit tried in Edinburgh from July 29th to-

August 4th, 1853. A lease had been granted by Mr and Mrs Gillespie, of Torbanehill, in Fifeshire, to Messrs Jamesnbsp;Russell and Son, coal-masters of Falkirk, of �the whole coal,nbsp;ironstone, iron-ore, limestone and fire-clay (but not to comprehend copper, or any other minerals whatsoever, except thosenbsp;specified) with lands of Torbanehill*.� After the Boghead hadnbsp;been worked for two years the Gillespies challenged the right ofnbsp;Messrs Russell, and argued that the valuable mineral Torhanitenbsp;was not included among the substances named in the agreement.nbsp;The defendants maintained that it was a coal, known asnbsp;gas-, cannel- or pari�ot-coal. A verdict was given for the defendants. Some of the scientific experts who gave evidencenbsp;at the trial considered that the Boghead afforded indications ofnbsp;organic structure, while others regarded it as essentially mineralnbsp;in origin.

The Torhanite or Boghead is a close-grained brown rock, of peculiar toughness and having a subconchoidal fracture. Itnbsp;contains about 6�7o carbon, with some hydrogen, oxygen,nbsp;sulphur, and mineral substances. A thin section examinednbsp;under the microscope presents the appearance of a dark andnbsp;amorphous matrix, containing numerous oval, spherical andnbsp;irregularly shaped bright orange-yellow patches. Fig. 36, 1nbsp;shows the manner of occurrence of the yellow bodies in a piecenbsp;of Scotch Boghead, as seen in a slightly magnified horizontalnbsp;section. Under a higher power the light patches in the figurenbsp;reveal traces of a faint radial striation, which in some casesnbsp;suggests the occurrence of a number of oval or polygonal cells.

TheAutun Boghead possesses practically the same structure. The yellow bodies are often sufficiently abundant to impart anbsp;bright yellow colour to a thin section. If the section isnbsp;vertical the coloured bodies are seen to be arranged in more ornbsp;less regular layers parallel to the plane of bedding.

The Kerosene shale of New South Wales agrees closely with the Scotch and French Boghead; it is approximately ofnbsp;the same geological age, and is largely made up of orange ornbsp;yellow bodies similar to those of the European Boghead, butnbsp;much more clearly preserved.

The nature and manner of formation of the various forms of coal should be dealt with in a later chapter devoted to thenbsp;subject of plants as rock-builders, but in view of the recentnbsp;statements as to the algal nature of these bituminous depositsnbsp;it may not be out of place to state briefly the main conclusionsnbsp;of the French authors.

MM. Renault and Bertrand regard each of the yellow bodies in the European and Australian Boghead as the thallus of annbsp;alga. To the form which is most abundant in the Kerosenenbsp;shale they have given the generic name of Reinschia, whilenbsp;that in the Scotch and French Boghead is named Pila.

A section of a piece of Kerosene shale at right angles to the bedding appears to be made up of fairly regular layers ofnbsp;flattened elliptical sacs of an orange or yellow colour. Each sacnbsp;or thallus is about 300/x in length and 1.50/u. broad (fig. 36, 3).nbsp;A single row of cells constitutes the wall surrounding thenbsp;central globular cavity. The cells are more or less pyriform innbsp;shape, and the cell-cavities are filled with a dark substance,nbsp;described by Renault and Bertrand as protoplasm, and the cell-

2. nbsp;nbsp;nbsp;Pila Mbractensis from the Autun Boghead, x 282 (after Bertrand).

3. nbsp;nbsp;nbsp;Reinschia Australis, from the Kerosene shale of New South Wales, x 592nbsp;(after Bertrand).

walls are fairly thick. lu some of the larger specimens there are often found a few smaller sacs enclosed in the cavity of thenbsp;partially disorganised mother-thallus. In the larger specimensnbsp;the wall is usually invaginated in several places, giving thenbsp;whole thallus a lobed or brain-like appearance. The supposednbsp;alga, which makes up ^ths of the contents of a block ofnbsp;Kerosene shale, is named Reinschia Australis; it is regardednbsp;by the authors of the species as nearly related to the Hydro-dictyaceae or Volvocineae.

In the Kerosene shale from certain localities in New South Wales Bertrand recognises a second form of thallus, which henbsp;refers to the genus Pila, characteristic of the European Bogheads.

The �thallus� characteristic of the Scotch Boghead has been named Pila scotica, and that of the Autun Boghead, Pilanbsp;bibractensis.

In the latter form, which has been studied in more detail by MM. Renault and Bertrand, the thallus consists of aboutnbsp;6�700 cells, and is irregularly ellipsoidal in form, from T89�nbsp;�225mm. in length, and 'ISG��lOOmm. broad. The surface-cells are radially disposed and pyramidal in shape, the internalnbsp;cells are polygonal in outline and less regularly arrangednbsp;(fig. 36, 2). The Pila thalli make up fths of the mass in annbsp;average sample of the Autun Boghead. The Autun Bogheadnbsp;often contains siliceous nodules, and sections of these occasionallynbsp;include cells of a Pila in which the protoplasmic content.s andnbsp;nuclei have been described by the French authors. The evidencenbsp;for the existence of these supposed nuclei is, however, not entirelynbsp;satisfactory; sections of silicified thalli which were shown tonbsp;me by Prof. Bertrand did not satisfy me as to the minutenbsp;histological details recognised by Bertrand and Renault.

The species of Pila are compared with the recent genus Gelastrum, and regarded as most nearly allied to the Chroococ-caceae or Pleurococcaceae among recent algae. Prof. Bornet'nbsp;has suggested Gomphosphaeria as a genus which presents anbsp;resemblance to the Autun Pila.

In addition to the Bogheads of Autim, Torbanehill, and New South Wales, there are similar Palaeozoic deposits innbsp;Russia, America, and various other parts of the world. Fullnbsp;details of the structure of Boghead and the supposed algaenbsp;referred to Reinschia, Pila, and other genera will be found innbsp;the writings of Bertrand and Renault*.

The Kero.sene shale of New South Wales affords the most striking and well-preserved examples of the cellular orange andnbsp;yellow bodies referred to as the globular thalli of algae. It isnbsp;almost impossible to conceive a purely inorgardc materialnbsp;assuming such forms as those which occur in the Australiannbsp;Boghead. On the other hand, it is hardly less easy tonbsp;understand the possibility of such explanations as have beennbsp;suggested of the organic origin of these characteristic bodies.

The ground-mass or matrix of the Boghead is referred to a brown ulmic precipitate thrown down on the floor of a Permiannbsp;or Carboniferous lake, probably under the action of calcareousnbsp;water. In this material there accumulated countless thalli ofnbsp;minute gelatinous algae, which probably at certain seasonsnbsp;completely covered the surface of the waters, as thenbsp;nbsp;nbsp;nbsp;d�eau

in many of our fresh-water lakes. In addition to the thalli of Reinschia and Pila the Bogheads contain a few remains ofnbsp;various plant fragments, pollen-grains, and pieces of wood.nbsp;Fish-scales and the coprolites of reptiles and fishes occur in somenbsp;of the beds. On a piece of Kerosene shale in the Woodwardiannbsp;Museum, Cambridge, there are two well-preserved graphiticnbsp;impressions of the tongue-shaped fronds of Glossopteris Browni-ana, Brongn. There can be little doubt that the beds ofnbsp;Boghead were deposited under water as members of a regularnbsp;sequence of sedimentary strata. The yellow bodies which formnbsp;so great a part of the beds are practically all of the same type.nbsp;Reinschia and Pila cannot always be distinguished, and itnbsp;would seem that there are no adequate grounds for institutingnbsp;two distinct genera and referring them to different families ofnbsp;recent algae.

1 Bertrand (93), Bertrand and Benault (92) (94), Bertrand (96), Renault (96). Additional references may be found in these memoirs.

French authors may be deiinite organic bodies, but it is unwise to attempt to determine their affinities within suchnbsp;narrow limits as have been referred to in the above r�sum�.nbsp;The structure of the bituminous deposits is worthy of carefulnbsp;study, and it is by no means impossible that further researchnbsp;might lead us to accept the view of the earlier investigators,nbsp;that the brightly coloured organic-like bodies may be inorganicnbsp;in origin.

The thallus of the members of this group assumes various forms, and consists of branched cell-filaments of a more or lessnbsp;complex structure. Cells of the thallus contain a red colouringnbsp;matter in addition to the green chlorophyll. The reproductionnbsp;is asexual and sexual; the formation of asexual reproductivenbsp;cells (tetraspores) in groups of four in sporangia is a characteristic method of reproduction. Sexual reproduction is effectednbsp;by means of distinct male and female cells.

With the exception of a few fresh-water genera all the red algae are marine. The Rhodophyceae, like the Cyanophyceaenbsp;and Chlorophyceae, include a shell-boring form which has beennbsp;found in the common razor-shellk Several genera live asnbsp;endophytes in the tissues of other algae. The recent speciesnbsp;of this section of algae are characteristic of temperate andnbsp;tropical seas. One subdivision of the red algae, the Coral-linaceae, is extremely important from a geological point of viewnbsp;and mu.st be dealt with in some detail.

The thallus is usually encrusted with carbonate of lime; it is of a branched cylindrical form in the well-known Corallinanbsp;officinalis, Linn, of the British coasts, of an encrusting andnbsp;foliaceous type, in the genus Lithophyllum, and of a more corallike form in the genus Lithothamnion. The reproductive organsnbsp;occur in conceptacles, having the form of small depressed

cavities in the thalliis, or projecting as warty swellings above the surface of the plant. Asexual reproduction is by meansnbsp;of tetraspores formed in conceptacles resembling those containing the sexual cells. The Corallinaceae may be subdividednbsp;into the two families Melobesieae and Corallineae^.

The genus Corallina is the best known British representative of the Corallinaceae. With other members of the group it wasnbsp;long regarded as a coralline animal, and it is only comparativelynbsp;recently that the plant-nature of these forms has been generallynbsp;admitted. Lithophyllum, Lithothamnion, Melohesia, and othernbsp;genera of the Corallinaceae and some of the Siphoneae f^laj' anbsp;very important part in the building and cementing of coral-reefs. The pink or rose-coloured calcareous thallus of some ofnbsp;these calcareous algae or Nullipores imparts to coi-al-reefs anbsp;characteristic appearance. In some cases, indeed, the coral-reefs are very largely composed of algae. Saville Kent^nbsp;describes the Corallines or Nullipores of the Australian Barrier-reef as furnishing a considerable quota towards the compositionnbsp;of the coral rock. Mr Stanley Gardiner, who accompanied thenbsp;coral-boring expedition to the island of Funafuti, has kindlynbsp;allowed me to quote the following extract from his notes, whichnbsp;affords an interesting example of the importance of calcareousnbsp;algae as reef-building organisms. �It is quite a misnomer to speaknbsp;of the outer edge of a reef like this (Rotuma Island) as beingnbsp;formed of coral. It would be far better to call it a Nulliporenbsp;reef, as it is completely encrusted by these algae, while outsidenbsp;in the perfectly clear water, 10 to 15 fathoms in depth, thenbsp;bottom has a most brilliant appearance from masses of red,nbsp;white and pink Nullipores, with only a stray coral here andnbsp;there.�

Agassiz^ has given an account of the occurrence of immense masses of Nullipores {Udotea, Halimeda etc.) in the Floridanbsp;reefs; his description is illustrated by good figures of thesenbsp;algae.

In the Mediterranean there are true Nullipore reefs, which are interesting geologically as well as botanically. Walther^nbsp;has described one of these limestone-banks in the Gulf ofnbsp;Naples which occurs about 1 kilometre from the coast aird 30nbsp;metres below the surface of the water. Every dredging, henbsp;say.s, brings up numberless masses of Lithothamnion fascicidatumnbsp;(Lamarck), and L. crassum (Phil.). Between the branches of thenbsp;algae, gasteropods and other animals become completely enclosednbsp;by the growing plants, while diatoms, foraminifera, and othernbsp;forms of life are abundant. Water percolating through thenbsp;mass gradually destroys the structure of the algal thalli, andnbsp;in places reduces the whole bank to a compact structurelessnbsp;limestone.

The same author� has also called attention to the importance of Lithophyllum as a constructive element in the coral-reefs offnbsp;the Sinai peninsula.

Philippi'* was the first writer to describe this and other genera as plants. He gave the following definition of Lithothamnion :

�Stirps calcarea rigida, e ramis oylindricis vel compressiiisculi.s dichotoma ramosis constans.quot;

The thallus of Lithothamnion grows attacljed to the face of a rock or other foundation, and forms a hard, stony mass, assumingnbsp;various coralline shapes. The exposed face may have the formnbsp;of numerous short branches or of an irregular warty surface.

In section (fig. 37, A.) the lower part of the thallus is seen to be made up of rows of cells radiating out from a central point,

B. nbsp;nbsp;nbsp;Section of Lithothamnion sugammi, Both (after Eothpletz-, x 100).

C. nbsp;nbsp;nbsp;A conoeptacle with tetraspores from a Tertiary Lithothamnion (after

and the, upper portion consists of vertical and horizontal rows of cells. The whole body is divided up into a large number ofnbsp;small cells by anticlinal and periclinal walls, and possesses annbsp;evident cellular as distinct from a tubular structure. Con-ceptacles containing reproductive organs are either sunk in thenbsp;thallus or project above the surface. The two types of structurenbsp;in a single thallus are shown in fig. 37, A, also a conceptaclenbsp;containing tetraspores.

In the closely allied Lithophyllum the thallus is encrusting, and in section it presents the same appearance as the lowernbsp;part of a Lithothamnion thallus.

Species of Lithothamnion occur in the 'Mediterranean Sea, and are abundant in the arctic regions^ while on the Britishnbsp;coasts the genus is represented by four species�. Some large

specimens of Lithothamnion and Lithophyllum are exhibited in one of the show-cases in the botanical department of the Britishnbsp;Museum. For the best figures and descriptions of recent speciesnbsp;reference should be made to the works of Hauck, Rosanoff,nbsp;Rosenvinge, Kjellman and Solms-Laubach'.

It is to be expected that such calcareous algae as Lithothamnion should be widely represented by fossil forms. In addition to the botanical importance of the data furnished bynbsp;the fossil species as to the past history of the Corallinaceae,nbsp;there is much of geological interest to be learnt from a study ofnbsp;the manner of occurrence of both the fossil and recent representatives. As agents of rock-building the coralline algae arenbsp;especially important. The late Prof linger^ in 18.58 gave annbsp;account of the so-called Leithakalk of the Tertiary Viennanbsp;basin, and recognised the importance of fossil algae as rockforming organisms. The Miocene Leithakalk, which is widelynbsp;used in Vienna as a building stone�, consists in part of limestonenbsp;rocks consisting to a large extent of Lithothamnion.

Since the publication of Unger�s work several writers have described numerous fossil species of lAthotkamnion from variousnbsp;geological horizons. A few examples will suffice to illustratenbsp;the range and structure of this and other genera of thenbsp;Corallinaceae. In dealing with the fossil species it is oftennbsp;impossible to make use of those characters which are of primarynbsp;importance in the recognition of recent species. The fossilnbsp;thallus is usually too intimately associated with the surroundingnbsp;rock to admit of any use being made of external form as-anbsp;diagnostic feature. The size and form of the cells must benbsp;taken as the chief basis on which to determine specific differences. In the absence of conceptacles or reproductive organs itnbsp;is not always easy to distinguish calcareous algae from fossilnbsp;Hydrozoa or Bryozoa. In many instances, however, apart fromnbsp;the nature and size of the elements composing the thallus, thenbsp;conceptacles afford a valuable aid to identification. An example

1 Hauck (85). Eosanoff (66). Eosenvinge (93) p. 779. Kjellman (83) p. 88. Solms-Laubach (81).nbsp;nbsp;nbsp;nbsp;^ Unger (58).

^ A microscopic section of the Vienna Leithakalk is figured in Nicholson and Lydekker�s Manual of Paleontology (89) vol. ii. p. 1497.

of a fossil conceptacle containing tetraspores is shown in fig. 37, C; it is from a Tertiary species of Lithothamnioa, describednbsp;by Friih from Mont�vraz in Switzerland.

1. nbsp;nbsp;nbsp;Lithotliamnion maniillosum G�inb. Fig. 32, A (i) and (ii).nbsp;(p. 155.) This species was first recorded by GlimbeF from thenbsp;Upper Cretaceous (Danian) rocks of Petersbergs, near Ma�stricht,nbsp;on the Belgian frontier. It was originally described as a Bryozoan.nbsp;The thallus has the form of an encrusting calcareous structurenbsp;bearing on its upper surface thick nodular branches, as shownnbsp;in fig. 32, A (ii); in section, A (i), the thallus consists of anbsp;regular series of rectangular cells.

The specific name maniillosum has also been given to a recent species by Hauck^, but probably in ignorance of thenbsp;existence of Giimbel�s Cretaceous species.

2. nbsp;nbsp;nbsp;Lithothamnion suganuni Roth. Fig. 37, B. The sectionnbsp;of this form given in fig. 37, B shows three oval conceptaclesnbsp;filled with crystalline material. The two lower conceptaclesnbsp;originally communicated with the surface of the thallus, butnbsp;as in recent species the deeper portions of the algal bodynbsp;became covered over by additions to the surface, formingnbsp;merel}� dead foundations for new and overlying living tissues.

The specimen wms obtained from a Lithothamnion bank, probably of Upper Oligocene age, in Val Sugana^, in thenbsp;Austrian Tyrol.

Numerous other species of Jurassic, Cretaceous and Tertiary age might be quoted, but the above may suffice to illustrate thenbsp;general characters and mode of occurrence of the genus. It isnbsp;important that the student should become familiar with thenbsp;Lithothamnion and Lithophyllum types of thallus, in view of theirnbsp;frequent occurrence in crystalline limestone rocks and in suchnbsp;comparatively recent deposits as those of upraised coral-reefs.nbsp;The coral-rock of Barbadoes and other West-Indian islands

affords a good illustration of the manner of occun�ence of fossil coralline algae in association with corals and other organisms^

In the fossil species of Lithothamnion hitherto recorded there do not appear to be any important features in which they differnbsp;from recent forms ; the geological history of the genus so far asnbsp;it is known, favours the view that the generic characters are ofnbsp;considerable antiquity.

Mr A. Brown'-', of Aberdeen, has recently brought forward good evidence for including various calcareous fossils, describednbsp;by several authors under different names and referred to variousnbsp;genera of fossil animals, in the genus Solenopora, which henbsp;places among the coralline algae.

Species of this genus have been described from England, Scotland, Esthonia, Russia, and other countries. The geologicalnbsp;range of Solenopora appears to be from Ordovician to Jurassicnbsp;rocks; in some cases it is an important constituent of beds ofnbsp;limestone.

Solenopora compacta (Billings). Fig. 38. This species was originally described by Billings as Stroniatopora compacta,

� Vide Walther (88) p. 499; also Jukes-Browne and Harrison (91) passim. I am indebted to Mr G. F. Pranks, -who has studied the Barbadian reefs, fornbsp;the opportunity of examining sections of quot;West-Indian coral-rock.

and afterwards defined by Nicholson and Etheridge. The thallus forms sub-spheroidal masses, from the size of a hemp-seed to that of an orange. The external surface is lobulate ;nbsp;the fractured surface has a poroellanous and sometimes anbsp;fibrous appearance, and is usually white or light brown innbsp;colour. In vertical section (fig. 38, B) the cells are elongatednbsp;and arranged in a radiating and parallel fashion; they oftennbsp;occur in concentric layers. The cells have a diameter of about

tangential section (fig. 38, A). Brown describes certain larger cells in the thallus (fig. 38, A) as sporangia^ but it is difficultnbsp;to recognise any distinct sporangial cavities in the drawing.nbsp;The example figured is from the Trenton limestone of Canada;nbsp;a variety of the same species has been recorded from the Ordovician rocks of Girvan in Ayrshire. There appear to be goodnbsp;reasons for accepting Brown�s conclusion that Solenopora belongsnbsp;to the Corallinaceae rather than to the Hydrozoa, among whichnbsp;it was originally included. After comparing Solenopora withnbsp;recent genera of Florideae, Brown concludes that �the formsnbsp;of the cells and cell-walls, the method of increase, and thenbsp;arrangement of the tissue cells in the various species ofnbsp;Solenopora bear strong evidence of relationship between thatnbsp;genus and the calcareous algae^.�

The importance of the calcareous Rhodophyceae has been frequently emphasised by recent researches, and our knowledgenbsp;of the rock-building forms is already fairly extensive. Wenbsp;possess evidence of the existence of species of different generanbsp;in Ordovician seas, as well as in those of the Silurian, Triassic, gt;nbsp;Jurassic, and more recent periods. It is reasonable to prophesynbsp;that further researches into the structure of ancient limestonesnbsp;will considerably extend our knowledge of the geological andnbsp;botanical history of the Corallinaceae.

Numerous fossils have been described as examples of other genera� of Rhodophyceae than those included in the Corallinaceae, but these possess little or no scientific value and neednbsp;not be considered.

Olive-brown algae, thallus often leathery in texture, composed of cell-filaments or parenchymatous tissue, in some cases exhibiting a considerable degree of internal differentiation. Thenbsp;sexual reproductive organs may be either in the form of passivenbsp;egg-cells and motile antherozoids or of motile cells showing nonbsp;external sexual difference.

With one or two exceptions all the genera are marine. They have a wide distribution at the present day, and arenbsp;especially characteristic of far northern and extreme southernnbsp;latitudes. The gigantic forms Lessonia, Macrocystis and othersnbsp;already alluded to, belong to this group; also the genus 8ar-gassum, of which the numberless floating plants constitute thenbsp;characteristic vegetation of the Sargasso Sea.

Palaeobotanical literature is full of descriptions of supposed fossil representatives of the brown algae, but only a few of thenbsp;recorded species possess more than a very doubtful value; mostnbsp;of them are worthless as trustworthy botanical records. Manynbsp;of the numerous impressions referred to as species of Fucoidesnbsp;and other genera present a superficial resemblance to the thallusnbsp;of the common Bladder-wrack and other brown seaweeds.nbsp;Such similarity of form, however, in the case of flat andnbsp;branched algal-like fossils is of no scientific value. In manynbsp;instances the impressions are probabl}quot; those of an alga, butnbsp;they are of no botanical interest. The flat and forked type ofnbsp;thallus of Focus, Chondrus crispus (L.) and other members ofnbsp;the Phaeophyceae is met with also among the red and greennbsp;algae, to say nothing of its occurrence in the group of thalloidnbsp;Liverworts, or of the almost identical form of various membersnbsp;of the animal kingdom. The variety of form of the thallus innbsp;one species is well illustrated by the common Chondrus crispusnbsp;(L.). This alga was described by Turner^ in his classic work onnbsp;the Fuci under the name of Focus crispus as � a marinenbsp;Proteus.� It affords an interesting example of the differentnbsp;appearance presented by the same species under different conditions, and at the same time it furnishes another proof of thenbsp;1 Turner (11) vol. ii. p. 51.

futility of relying on imperfectly preserved external features as taxonomic characters of primary importance.

An example of a supposed Jurassic Fucus is shown in fig. 49, and briefly described in the Chapter dealing with fossil Bryo-phytes.

Several species of Flysch Algae have recently been referred by Rothpletz^ to the Phaeophyceae under the provisionalnbsp;generic name Phycopsis, but they are of no special botanicalnbsp;interest.

The extremely interesting genus Nematophycus has lately been assigned by a Canadian author^ to a position in thenbsp;Phheophyceae. Although the particular points on which henbsp;chiefly relies are not perhaps thoroughly established, therenbsp;are certain considerations which lead us to include Nematophycus as a doubtful member of the present group of algae.

The stem attains a diameter of between 2 and 3 feet in the largest specimens; it is made up either of comparatively widenbsp;and loosely arranged tubes pursuing a slightly irregular verticalnbsp;course accompanied by a plexus of much narrower tubes, or ofnbsp;tubes varying in diameter but not divisible into two distinctnbsp;types. Rings of growth occur in some forms but not in others.nbsp;Radially elongated or isodiametric spaces occur in the stemnbsp;tissues in which the tubes are less abundant.

Reproductive organs unknown, with the possible exception of some very doubtful bodies described as spores.

In 1856 Sir William Dawson proposed the generic name Prototaadtes for some large silicified trunks discovered in thenbsp;Lower and Middle Devonian rocks of Canada. A few yearsnbsp;later the same writer� published a detailed account of the newnbsp;fossils and arrived at the conclusion that the Devonian stemnbsp;showed definite points of affinity with the recent genus Taxus,nbsp;and the generic name suggests that he regarded it as the typenbsp;of Coniferous trees belonging to the sub-family Taxineae. The

Hothpletz (96). nbsp;nbsp;nbsp;� Penhallow (96) p. 45.nbsp;nbsp;nbsp;nbsp;� Dawson (59).

reasons for this determination were afterwards shown by Car-ruthers to be erroneous. Dawson thought he recognised pits and spiral thickenings in the walls of the tubular elements,nbsp;as well as pointed ends in some of the latter. The spiralnbsp;markings were in reality small hyphal tubes passing obliquelynbsp;across the face of the wider tubes, and the apparent ends of thenbsp;supposed tracheids were deceptive appearances due to the factnbsp;that the tubes had in some cases been cut through in an obliquenbsp;direction. In 1870 Carruthers^ expressed the opinion thatnbsp;Dawson�s Prototaxites was a � colossal fossil seaweed � and not anbsp;coniferous plant. The same author^ in 1872 published a fullnbsp;and able account of the genus, and conclusively proved thatnbsp;Prototaxites could not be accepted as a Phanerogam; henbsp;brought forward almost convincing evidence in favour ofnbsp;including the genus among the algae. The name Prototaxitesnbsp;was now changed for that of Nematophycus. Carruthers compares the rings of growth in the fossil stems with those in thenbsp;large Antarctic Lessonia stems, but he regards the histologicalnbsp;characters as pointing to the Siphoneae as the most likelynbsp;group of recent algae in which to include the Palaeozoic genus.

We may pass over various notes and additional contributions by Dawson, who did not admit the corrections to his originalnbsp;descriptions which Carruthers� work supplied. In 1889 annbsp;important memoir appeared by Penhallow� of Montreal innbsp;which he confirmed Carruthers� decision as to the algal naturenbsp;of Prototaxites ; he contributed some new facts to the previousnbsp;account by Carruthers, and expressed himself in favour ofnbsp;regarding the fossil plant as a near ally of the recent Lamin-ariae. The next addition to our botanical knowledge of thisnbsp;genus was made by Barber^ who described a new specific type ofnbsp;Nematophycus�N.Storriei�found by Storrie in beds of Wenlocknbsp;limestone age near Cardiff. Solms-Lauhach�, in a recent memoirnbsp;on Devonian plants, recorded the occurrence of another speciesnbsp;of this genus in Middle Devonian rocks near Grafrath on thenbsp;Lower Rhine. Lastly Penhallow�, in describing a new^ species,

lays stress on the resemblance of some of the tubular elements in the stem to the sieve-hyphae of the recent seaweeds Macro-cystis and Laminaria. He concludes that the new facts henbsp;records make it clear that Nematophycus � is an alga, and ofnbsp;an alliance with the Laminarias.� The recent evidence broughtnbsp;forward by Penhallow is not entirely satisfactory; the drawingsnbsp;and descriptions of the supposed trumpet-shaped sieve-hyphaenbsp;are not conclusive. On the whole it is probably the betternbsp;course to speak of Nematophycus as a possible ally of thenbsp;brown algae rather than as an extinct type of the Siphoneae,nbsp;but until our knowledge is more complete it is practicallynbsp;impossible to decide the exact position of this Siluro-Devoniannbsp;genus.

Solms-Laubach�^ has suggested that the generic name Nema-tophyton, used by Penhallow in preference to Carruthers� term Nematophycus, is the more suitable as being a neutral designation and not one which assumes a definite botanical position.nbsp;In view of the nature of the evidence in favour of the algalnbsp;affinities of the fossil, the reasons for discarding Carruthers�nbsp;original name are hardly sufficient.

Before discussing more fully the distribution and botanical position of Nematophycus we may describe at length one of thenbsp;best known species, and give a short account of some other forms.

1. Nematophycus Logani (Daws.). Fig. 39, A�E. The stem possesses well marked concentric rings of growth due tonbsp;a periodic difference in size of the large tubular elements.nbsp;The tissues consist of two distinct kinds of tubular elements,nbsp;the larger tubes loosely arranged and pursuing a fairly regularnbsp;longitudinal course, and having a diameter of 13-35 p,; thenbsp;smaller tubes, with a diameter of 5-6 g, ramify in differentnbsp;directions and form a loose plexus among the larger and morenbsp;regularly disposed elements. Branching occurs in both kindsnbsp;of tubes; septa have been recognised only in the smaller tubes.nbsp;Irregular and discontinuous radial spaces traverse the stemnbsp;tissues, having a superficial resemblajnce in their manner ofnbsp;occurrence to the medullary rays of the higher plants.

The best specimens of this species were obtained by Sir William Dawson from the Devonian Sandstones of Gaspe innbsp;New Brunswick. The largest stems had a diameter of 3 feetnbsp;and reached a length of several feet^; in some examplesnbsp;Dawson found lateral appendages attached to the stem whichnbsp;he described as � spreading roots.� Externally the specimensnbsp;were occasionally covered with a layer of friable coal, andnbsp;internally the tissues were found to be more or less perfectlynbsp;preserved by the infiltration of a siliceous solution. Most ofnbsp;the examples of Nematophycus from Britain and Germany arenbsp;much smaller and less perfectly preserved than those fromnbsp;Canada. The Peter Redpath Museum, Montreal, containsnbsp;several very large blocks of Nematophycus, in many of whichnbsp;one sees the concentric rings of growth clearly etched out bynbsp;weathering agents in a cross section of a large stem.

In fig. 39, A, a sketch is given of a thin transverse section of a stem, drawn natural size. The lines of growth are clearlynbsp;seen, and as in coniferous stems the breadth of the concentricnbsp;zones varies considerably. The short lines traversing thenbsp;tissues in a radial direction represent the medullary-ray-likenbsp;spaces referred to in the specific diagnosis. A transverse sectionnbsp;examined under a low-power objective presents the appearancenbsp;of a number of thick-walled and comparatively wide tubesnbsp;loosely arranged; they may be in contact or separated fromnbsp;one another. If the microscope be carefully focussed through thenbsp;thickness of the section the transversely-cut tubes appear to movenbsp;laterally, producing a curiously dazzling effect if the objectivenbsp;is raised or lowered rapidly. This lateral movement is duenbsp;to the undulating vertical course of the tubes. Under anbsp;higher power the lighter-coloured matrix in which the tubesnbsp;are embedded shows a number of very much smaller andnbsp;thinner-walled hyphal elements; some of these are cut acrossnbsp;transversely, others more or less obliquely and others againnbsp;longitudinally. These smaller tubes constitute an irregularnbsp;plexus surrounding and ramifying between the larger elements.nbsp;The diameter of the larger tubes decreases for a certainnbsp;distance in a radial direction as seen in a transverse section,

Fig. 39. Nematophycus Logani {Davis.). A. Part of a transverse section from a specimen in the British Museum. (Nat. size.) B. Transverse section fromnbsp;specimens in Mr Barber�s possession. C. Longitudinal section. (B andnbsp;C X 160.) D. Transverse section showing a radial space. E. Transversenbsp;section; a few �cells� more highly magnified. D and E from a specimennbsp;in the British Museum.

and this change in size gives rise to the appearance of concentric lines indicating periodic changes in growth.

The radial spaces are characterised by the partial absence of the larger tubes, and as seen in longitudinal sections these spacesnbsp;constitute regions in which the smaller tubes branch very freely.nbsp;Fig. 39, B, represents a small piece of a transverse section seennbsp;under a fairly high power. In fig. 39, C, the tubes are seen innbsp;longitudinal section. The larger elements are unseptate andnbsp;not very regular in their vertical course through the stem; thenbsp;smaller elements are seen as fine tubes lying between and acrossnbsp;the larger tubes. In the sections I have examined no undoubted transverse septa were detected in any of the tubularnbsp;elements.

The question as to the possible connection between the larger and smaller elements is one which is not as yet satisfactorily disposed of. Penhallow^ regards the finer hyphal elementsnbsp;as branches of the larger tubes, but Barber�, who has carefullynbsp;examined good material of Nematophycus Logani, was unable tonbsp;detect any organic connection between the two. My ownnbsp;observations are in accord with those of Barber. Furthernbsp;details and numerous figures of this species of Nematophycusnbsp;will be found in the memoirs of Carruthers, Penhallow andnbsp;Barber,

Some specimens of silicified Nematophycus stems afford particularly instructive examples of the state of preservation or method of mineralisation as a source of error in histologicalnbsp;work. The sketches reproduced in fig. 39, D and E, were madenbsp;from a section of a large specimen of Nematophycus in thenbsp;British Museum. In fig. D we have one of the radial spacesnbsp;containing some indistinct small elements, the tissue sur-rounding the space appears to consist of poly^gonal cellsnbsp;suggesting ordinary parenchymatous tissue. In fig. E a few ofnbsp;these �cells� are seen more clearly, they have black and raggednbsp;walls, and often contain very small and faint circles of whichnbsp;the precise nature is uncertain. The true interpretation of

this form of structure was first supplied by Penhallowb The black network simulating parenchymatous tissue consists ofnbsp;the substance of Nematophycus txibes which has been completely redistributed during fossilisation and collected alongnbsp;fairly regular lines, as seen in figs. D and E. The originalnbsp;structure has been almost completely destroyed, and thenbsp;material composing the walls of the large tubes has finally beennbsp;rearranged as a network, interrupted here and there by thenbsp;characteri.stic radial spaces which remain as evidence of thenbsp;original Nematophycus characters. It is possible in some casesnbsp;to trace every gradation from sections exhibiting the normalnbsp;structure through those having the appearance shown innbsp;figs. D and E to others in which the structure is completelynbsp;lost. Penhallow describes this method of fossilisation in N.nbsp;crassus (Daws.); an examination of several specimens in thenbsp;National Collection leads me to entirely confirm bis generalnbsp;conclusions, and also to the opinion that N. Logani showsnbsp;exactly the same manner of mineralisation as N. crassus. Thenbsp;chief point of interest as regards this method of preservationnbsp;lies in the fact that a fossil described by Dawson^ as Cellulo-xylon primaevum, and referred to as a probable conifer, isnbsp;undoubtedly a badly preserved Nematophycus. Penhallownbsp;examined Dawson�s specimens and obtained convincing evidence of their identity with certain forms of highly alterednbsp;Nematophycus stems.

2. Nematophycus Storriei Barber. Fig. 40. The specimens on which Barber^ founded this species were obtained bynbsp;Mr Storrie from the Tymawr' quarry near Cardiff, in beds ofnbsp;Wenlock age. The fragmentary nature of the material isnbsp;largely compensated for by the excellence of the preservation.nbsp;We may briefly define the species as follows:

The stem consists of separate interlacing undivided and usually unbranched tubes of varying diameter. Spaces morenbsp;or less isodiametric in dimensions are scattered through thenbsp;tissue. The spaces constitute regions in which the tubularnbsp;elements branch freely.

1 Penhallow (89) and (93). nbsp;nbsp;nbsp;^ Dawson (81) p. 302.nbsp;nbsp;nbsp;nbsp;^ Barber (92).

The main distinguishing features of this British species are (i) the absence of two distinct and well-defined forms of tubularnbsp;elements. The main part of the stem consists of thick walled

Pfb'..

Fig. 40. Nematophycus Storriei Barb. Longitudinal section, from a photograph by Mr C. A. Barber, x 45.

tubes similar to those of iV. Logani, but the spaces between them are occupied by thinner-walled and smaller tubes varyingnbsp;considerably in diameter; (ii) the form of the spaces which arenbsp;not radially elongated as in N. Logani.

Fig. 40 shows the undulating course of the tubes as seen in a longitudinal section; the black colour of some of the elementsnbsp;is due to the fact that the surface of the wall is seen, while innbsp;the lighter-coloured portions of the tubes the wall has been cutnbsp;through. The lighter patch about the middle of the figurenbsp;shows the form of one of the spaces in which the tubes arenbsp;freely branched.

In addition to the two species already described six others have been recorded, but with these we need not concernnbsp;ourselves in detail. One of these species, W. Hicksi, was foundnbsp;by Dr Hicks' in the Denbighshire grits quarry of Pen-y-Glognbsp;near Corwen in North Wales. The position of these beds has

recently been determined by Mr Lake^ as corresponding to that of the Wen lock limestone. This species and N. Storriei arenbsp;both Silurian examples of the genus. It is possible, as Barbernbsp;has suggested, that the specimens described under these twonbsp;names should be referred to one species. The specimens foundnbsp;by Hicks were small and imperfectly preserved fragments;nbsp;Etheridge has given a full description of their structure, andnbsp;Barber has subsequently examined the material. The preservation is not such as will admit of any very precise specificnbsp;diagnosis; the fragments are correctly referred to Nematophycus,nbsp;but their specific characters cannot be clearly determined.

Solms-Laubach^ has described some fragments of another species of Nematophycus from the Devonian rocks of the Lowernbsp;Rhine. His specimens are chiefly interesting as extending thenbsp;geographical range of the genus, and as affording examples of anbsp;curious method of preservation. The specimens obtained werenbsp;small fragments, flattened and very dark brown in colour. Thenbsp;tubular elements consisted of an external membrane of blacknbsp;coal, enclosing a central core of dark red iron-oxide. Onnbsp;burning the fragment on a piece of platinum foil the coalnbsp;composing the wall of the tubes was removed and the deep-rednbsp;casts of the tube-cavities remained�. The investigation of thenbsp;structural characters of this imperfect material was conductednbsp;by reflected light. Under certain conditions, when it is impossible to obtain thin sections for examination by transmittednbsp;light, it is possible to accomplish much, as shown by Solms-Laubach�s work, by means of observation with direct light.

The last species to be noticed is Nematophycus Ortoni recently described by Penhallow. There are no concentricnbsp;rings of growth, no radial spaces and no smaller hyphae in thenbsp;tissues of this type of stem. In longitudinal section, the tubesnbsp;show occasional local expansions of the lumen which Penhallownbsp;compares with the ' trumpet-hyphae � of some recent brownnbsp;algae. No actual sieve-plates or transverse walls have beennbsp;detected, but the general appearance of the tubes is considered

* A similar method of fossilisation has been noted by Eothpletz in the ease of the Lower Devonian alga Hostinella. [Eothpletz (96) p. 896.]

to afford distinct evidence of the original existeiice of such walls. The figures accompanying the description do not carrynbsp;conviction as to the correctness of the reference of the tubes tonbsp;imperfectly preserved sieve-hyphae.

The following list, taken, with a few alterations, from Penhallow�s memoir^ shows the geographical and geologicalnbsp;range of the species of Neniatophycus hitherto recorded.

In summing up our information as to the structure of Nemateyphycus we find there are certain points not definitelynbsp;settled, and which are of considerable importance. The few recorded instances of spore-like bodies by Penhallow and Barbernbsp;are not satisfactory; we are still ignorant of the nature of thenbsp;reproductive organs. Such instances of lateral appendages asnbsp;have been referred to do not throw much light on the habit ofnbsp;the plant. So far as we know at present the stem of Neniatophycus was not differentiated internally into a cortical andnbsp;central region. It may be that the � specimens have been onlynbsp;partially preserved, and the coaly layer which occasionallynbsp;surrounds a stem may represent a carbonised cortex which hasnbsp;never been petrified. The large and loosely arranged tubesnbsp;constitute the chief characteristic feature of the genus ; innbsp;some cases {N. Logani) there is an accompanying plexus ofnbsp;smaller hyphae, in others {N. Storriei) there is no definitenbsp;division of the tissue into two sets of tubes of uniform size, andnbsp;in N. Ortoni the tubular elements are all of the large type.

2 nbsp;nbsp;nbsp;Carruthers (72) p. 162 regards this species as identical with N. Logani.

Penhallow has recognised the branching of large tubes in N. Logani and N. crassus giving rise to the small hyphalnbsp;elements. In most specimens, however, no such mode of originnbsp;of the smaller tubes can be detected. The spaces whichnbsp;interrupt the homogeneity of the tissues in some forms havenbsp;been described as branching depots, on account of the frequentnbsp;occurrence in these areas of much branched hyphae. Thenbsp;function of these spaces (fig. 39, D, and fig. 40) may he connectednbsp;with aeration of the stem-tissues.

As Carruthers first pointed out the unseptate nature of the elements and the occurrence of large and small tubes formingnbsp;a comparatively lax tissue suggested affinities with such recentnbsp;genera as Penicillus, Halmeda, Udotea and other members ofnbsp;the Siphoneae. In those fos.sil stems which possess tubes ofnbsp;two distinct sizes, we cannot as a rule trace any organicnbsp;connection between the two sets of tubular elements. Transverse septa have been detected in the tubes of some specimensnbsp;of N. Logani. These considerations and the large size and habitnbsp;of growth of the stem leave one sceptical as to the wisdomnbsp;of assigning the fossil genus to the Siphoneae. On the othernbsp;hand, apart from the doubtful sieve-hyphae of Penhallow, thenbsp;manner of growth of the plant, the concentric rings, marked by anbsp;decrease in the diameter of the tubes, the lax arrangement andnbsp;irregular course of the elements, afford points of agreement withnbsp;some recent Phaeophyceae. The stem of a Laminaria (fig. 29)nbsp;or of a Lessonia are the most obvious structures with whichnbsp;to compare Nematophycus. The medullary region of a Laminaria or Fucus and of other genera presents a certain resemblancenbsp;to the tissues of the fossil stems. On the whole we may benbsp;content to leave Nematophycus for the present as probably annbsp;extinct type of alga, more closely allied to the large membersnbsp;of the Phaeophyceae than to any other recent seaweeds.

There is another fossil occasionally associated with Nematophycus and referred by many writers to the Algae, which calls

for a brief notice, Pachytheca is too doubtful a genus to justify a detailed treatment in the present work. Although, asnbsp;I have elsewhere suggestedh we are hardly in a position tonbsp;speak with any degree of certainty as to its affinity, it is notnbsp;improbable that it may eventually he shown to be an alga.

Without attempting a full diagnosis of the genus, we may briefly refer to its most striking characters.

Pachytheca usually occurs in the form of small spherical bodies, about 5 cm. in diameter, in Old Red Sandstone ornbsp;Silurian rocks. In section a single sphere is found to consistnbsp;of two well marked regions; in the centre, of a number ofnbsp;ramifying and irregularly placed narrow tubes, and in thenbsp;peripheral or cortical region, of numerous regular and radiallynbsp;disposed simple or forked septate tubes. The tubular elementsnbsp;of the two regions are in organic connection.

The name was proposed by Sir Joseph Hooker for some specimens found by Dr Strickland'^ in the Ludlow bone-bednbsp;(Silurian) of Woolhope and May-Hill. Examples were subsequently recorded from the Wenlock limestone of Malvern andnbsp;from Silurian and Old Red Sandstone rocks of other districts.nbsp;Hicks� found Pachytheca in the Pen-3r-Glog grits of Corwen innbsp;association with Nernatophyciis, and the two fossils have beennbsp;found together elsewhere. This association led to the suggestion that Pachytheca might be the sporangium of Nemato-phyc'us, and Dawson^, in conformity with his belief in tbenbsp;coniferous character of the latter plant, referred to Pachythecanbsp;as a true seed.

The best sections of this fossil have been prepared with remarkable skill by Mr Storrie of Cardiff; they were carefullynbsp;examined and described by Barber in two memoirs� publishednbsp;in the Annals of Botany, the account being illustrated by severalnbsp;well executed drawings and microphotographs.

Among other difficulties to contend against in the interpretation of Pachytheca there is that of mineralisation. The preservation is such as to render the discrimination of originalnbsp;.structure as distinct from structural features of secondary origin,

^ Seward (95^). nbsp;nbsp;nbsp;^ Strioklacd and Hooker (53).nbsp;nbsp;nbsp;nbsp;^ Hicks (81) p. 484.

consequent on a particular manner of crystallisation of the siliceous material, a matter of considerable difSculty.

Suggestions as to the nature of Pachyiheca have been' particularly numerous; it has been referred to most classes ofnbsp;plants and relegated by some writers to the animal kingdom.nbsp;The most recent addition to our knowledge of this problematicnbsp;fossil was the discovery of a specimen by Mr Storrie in whichnbsp;the Pachytheca sphere rested in a small cup, like an acorn fruitnbsp;in its cupule. This specimen was figured and described bynbsp;Mr George Murray^ in 1895; he expresses the opinion that thenbsp;discovery makes the taxonomic position of the genus still morenbsp;obscure. Solms-Laubach briefly refers to Pachytheca in connection with Nematophycus, and regards its precise naturenbsp;almost as much an unsolved riddle now as it was when firstnbsp;discovered. For a fuller account of this fossil reference mustnbsp;be made to the contributions of Hooker'^ Barber'� and others.nbsp;The literature is quoted by Barber and more recently bynbsp;Solms-Laubach^. There are several specimens and microscopicnbsp;sections of Pachytheca in the geological and botanical departments of the British Museum. The genus has been recordednbsp;from Shropshire, North Wales, Malvern, Herefordshire, Perthshire and other British localities, as well as from Canada; itnbsp;occurs in both Silurian and Old Red Sandstone rocks.

A generic name for those fossils which in all probability belong to the class Algae, but which, by reason of the absencenbsp;of reproductive organs, internal structure, or characters ofnbsp;a trustwortiiy nature in the determination of affinity, cannot benbsp;referred with any degree of certainty to a particular recentnbsp;genus or family.

This term was suggested in 1894� as a provisional and comprehensive designation under which might be included suchnbsp;impressions or casts as might reasonably be referred to Algae.nbsp;The practice of applying to alga-like fossils names suggestivenbsp;of a definite alliance with recent genera is as a rule unsound.

^ Murray G. (95-�). nbsp;nbsp;nbsp;� Hooker J. D. (89).nbsp;nbsp;nbsp;nbsp;^ loc. cit.

It would simplify nomenclature, and avoid the multiplication of generic names, if the term Algites were applied to such algalnbsp;fossils from rocks of various ages as afford no trustworthy datanbsp;by which their family or generic affinity can be established.

This class of organisms affords an interesting example of the impossibility of maintaining a hard and fast line between thenbsp;animal and plant kingdom. Zoologists and Botanists usuallynbsp;include the Myxomycetes� in the text-books of their respectivenbsp;subjects, and the name Animal-fungi which has been appliednbsp;to these organisms expresses their dual relationship. Theynbsp;constitute one of three groups which we may include in thatnbsp;intermediate zone or �' buffer-state � between the two kingdoms.nbsp;From a palaeobotanical point of view the Myxomycetes are ofnbsp;little interest, but a very brief reference may be made to themnbsp;rather for the sake of avoiding unnecessary incompleteness innbsp;our classification than from their importance as possible fossils.

They are organisms without chlorophyll, consisting of a naked mass of protoplasm, known as the plasmodium, whichnbsp;may attain a size of several inches. Such plasmodia creepnbsp;over the surface of decaying organic substrata, and in formingnbsp;their asexual reproductive cells they are converted into somewhat complex fruits containing spores. The spores producenbsp;motile swarm-cells, which eventually coalesce together to formnbsp;a new plasmodium.

A few examples of fossil Myxomycetes have been, recorded from the Palaeozoic and more recent formation.s, but none ofnbsp;them are entirely beyond suspicion. We may mention threenbsp;examples of fossils referred to this group, but only one of thesenbsp;is entitled to serious consideration.

1 nbsp;nbsp;nbsp;An excellent monograph on the Mycetozoa has lately been issued by thenbsp;Trustees of the British Museum under the authorship of Mr A. Lister (94). Videnbsp;also Sehr�ter (89) in Engler and Prantl�s Natiirlichen PJianzenfamilien.

distinct traces of original or secondary cell-contents in well preserved petrified plant-tissues. There is often a difficulty,nbsp;however, in distinguishing between the true cell-contents andnbsp;the cells of some parasitic or saprophytic intruder. In somenbsp;petrified corky tissue in a silicified nodule from the Permo-Carboniferous beds of Autun, Kenault has recently discoverednbsp;what he believes to be traces of a Myxomycetous plasmodium.nbsp;The cork-cells would be without protoplasmic contents of theirnbsp;own, and their cavities contain a number of fine strandsnbsp;stretching from the cell-walls in different directions and unitingnbsp;in places as irregular or more or less spherical masses. Thenbsp;drawings given by Renault of these irregular reticulated structures with scattered patches of what may possibly be petrifiednbsp;plasmodial protoplasm bear a striking resemblance to the plasmodium of a Myxomycete. A figure of the capillitium of a speciesnbsp;of Leocarpus figured by Schr�ter' in his account of the Myxo-mycetes in Engler and Prantl�s work is very similar to that ofnbsp;Renault�s � plasmodium.�

It is by no means inconceivable that the Myxomycetes Mangini may be correctly referred to this group, but the wisdomnbsp;of assigning a name to such structures may well be questioned.

The other two examples call for little notice. Messrs Cash and Hick� in a paper on fossil fungi from the Coal-Measuresnbsp;refer to some small spherical bodies as possibly the spores of anbsp;Myxomycete. They might be referred equally well to numerousnbsp;other organisms.

G�ppert and Menge� in their monograph on plants in the Baltic Tertiary Amber, express the opinion that an ill-definednbsp;tangle of threads which they figure may be a Myxomycete.

It would serve no useful purpose to quote other instances of possible representatives of fossil Mycetozoa; but the consideration of the above examples may serve to emphasize thenbsp;desirability of refraining from converting a possibility into annbsp;apparently recognised fact by the application of definite genericnbsp;and specific names.

The most striking difference between the fungi and algae is the absence of chlorophyll in the former, and the consequentnbsp;inability of fungi to manufacture their organic compounds fromnbsp;inorganic material. Fungi live therefore either as parasitesnbsp;or saprophytes, and as the same species may pass part of its lifenbsp;in a living host to occur at another stage of its development asnbsp;a saprophyte, it is impossible to distinguish definitely betweennbsp;parasitic and saprophytic forms. The vegetative body of anbsp;fungus, that is the portion which is concerned with providingnbsp;nourishment and preparing the plastic food-substance for thenbsp;reproductive organs, is known as the myceliuvi. It consistsnbsp;either of a single and branched tubular cell known as a hypha,nbsp;or of several hyphae or thread-like elements (filamentous fungi).nbsp;The hyphal filaments may be closely packed together and form anbsp;felted mass of compact tissue, which in cross section closelynbsp;simulates the parenchyma of the higher plants. This pseudo-parenchymatous form of thallus is particularly w^ell illustrated bynbsp;the so-called sclerotia; these are sharply defined and oftennbsp;tuberous masses of hyphal tissue covered by a firm rind andnbsp;containing supplies of food in the inner hyphae. They are ablenbsp;to remain in a quiescent state for some time, and to resistnbsp;unfavourable conditions until germination and the formationnbsp;of a new individual take place. The reproductive structuresnbsp;assume various forms; in some of the simpler fungi (Phy-comycetes) sexual organs occur, as in the parallel group ofnbsp;Siphoneae among the algae, but in the higher fungi thenbsp;reproduction is usually entirely asexual. An interesting casenbsp;has recently been recorded among the more highly�' differentiatednbsp;fungi in which distinct sexuality has been established'. Innbsp;addition to the reproductive organs, such as oogonia andnbsp;antheridia, the asexual cells or spores are borne either in specialnbsp;sporangia, or they occur as exposed conidia on supporting hyphaenbsp;or conidiophores. Thick-walled and resistant resting-spores ofnbsp;various forms are also met with.

Without going into further details we may very briefly refer to the larger subdivisions of this group of Thallophytes.

Chytridiaceae, amp;c. hyphae or by the fertilisation of an egg-cell contained in an oogonium.

Intermediate between the Phycomycetes and the higher fungi. Multicellular hyphae. Nonbsp;sexual organs.

Septate vegetative mycelium. No sexual reproduction�as a general rule. Asexual conidia and other forms of spores. In the Ascomycetes thenbsp;spores are foundin characteristicclub-shaped casesnbsp;or asci; in the Basidiomycetes the spores are bornenbsp;on special branches from swollen cells known asnbsp;basidia. The sporophore or spore-bearing bodynbsp;in this group may attain a considerable sizenbsp;(e.g. Agarious, Polyporus, amp;o.) and exhibit anbsp;distinct internal differentiation.

Before describing a few examples of fossil fungi, it is important to consider the general question of their manner ofnbsp;occurrence and determination. Considering the small size andnbsp;delicate nature of most fungi, it is not surprising that we havenbsp;but few satisfactory records of well-defined fossil forms. Thenbsp;large leathery sporophores of Polyporus and other genera ofnbsp;the Basidiomycetes, which are familiar objects as yellow or brownnbsp;brackets projecting from the trunks of diseased forest trees, havenbsp;been found in a fairly perfect condition in the Cambridgeshirenbsp;peat-beds, and examples have been described also by continentalnbsp;writers^ As a general rule, however, we have to depend onnbsp;the chance mineralisation or petrifaction of the hyphae of anbsp;fungus-mycelium which has invaded the living or dead tissuesnbsp;of some higher plant. In the literature on fossil plants therenbsp;are numerous recorded species of fungi founded on dark colourednbsp;spots and blotches on the impression of a leaf Most of suchnbsp;records are worthless; the external features being usually too

imperfect to allow of accurate identification. The occurrence of recent fungi as discolourations on leaves is exceedinglynbsp;common, and the characteristic perithecia or compact and morenbsp;or less spherical cases enclosing a group of sporangia in certainnbsp;Ascomycetous species, might be readily preserved in a fossilnbsp;condition.

Some examples of possible Ascomycetous fungi have been recently recorded by Potonie from leaves and other portions ofnbsp;plants of Permian age. There is a distinct superficial resemblance between the specimens he figures and the fructificationsnbsp;of recent Ascomycetes, but in the absence of internal structure,nbsp;it would be rash to do more than suggest the probable naturenbsp;of the markings he describes. For one of the fungus-likenbsp;impressions Potonie proposes the generic name Roselliniteshenbsp;compares certain irregularly shaped projections on a piece ofnbsp;Permian wood with the perithecia of Rosellinia, a member ofnbsp;the Sphaeriaceae, and describes them as Rosellinites Beyshlagiinbsp;Pot.^ Various other records of similar Ascomycetes-like fossilsnbsp;may be found in palaeobotanical literature ^ but it is unnecessary to examine these in detail. Unless we are able tonbsp;determine the nature of the supposed fungus by microscopicalnbsp;methods our identifications cannot in most cases be of any greatnbsp;value.

An example of the perithecia of a fungus {Rosellinia congregata [Beck])� has been recorded from the Oligocene ofnbsp;Saxony, which would appear to rest on a more satisfactory basisnbsp;than is often the case. In this particular instance the smallnbsp;projections on a piece of fossil coniferous stem present anbsp;form which naturally suggests a fungus perithecium. In casesnbsp;where the black spots on a fossil stem or leaf possess a definitenbsp;form and structure, it is perfectly legitimate to refer them to anbsp;group of fungi; but in very many instances the forms referrednbsp;to such genera as Sphaerites and others are of little or no value.

^ References are given by Potoni� to illustrations by Zeiller (92^) PI. xv. fig. 6, Grand� Eury (77) PI- xxxiii. fig. 7, and others in which possible fungi arenbsp;represented.

Many forms of scale-insects and galls on leaves present an obvious superficial resemblance to epiphyllous fungi, and might readilynbsp;be mistaken for the fructifications of certain Ascomycetousnbsp;species. As examples of scale-insects simulating fungi, referencenbsp;may be made to such genera of the Coccineae as As'pidiotus,nbsp;Diaspis, Lecanium, Coccus, and others. The female insects lyingnbsp;on the surface of a leaf, if preserved as a fossil impression, mightnbsp;easily be mistaken for perithecial

Another pitfall in fossil mycology may be illustrated by a description of a supposed fungus. Sclerotites Salishuriae^, Mass,nbsp;on a Tertiary Ginkgo leaf. The figure given by Massalongonbsp;represents a Ginkgo leaf with well marked veins, the laminanbsp;between the veins being traversed by short discontinuous andnbsp;longitudinally-running lines; the latter are referred to as thenbsp;fungus. In a recent Ginkgo leaf one may easily detect withnbsp;the naked eye a number of short lines between and parallelnbsp;to the veins, which if examined in section are found to benbsp;secretory canals. There can be little doubt that Sclerotitesnbsp;Salishuriae owes its existence to the preservation of thesenbsp;canals.

The list of fossil fungi given by Meschinelli in Saccardo�s Sylloge Fungorum^ includes certain species which are of nonbsp;botanical value, and should have no place in any list whichnbsp;claims to be authentic.

Among the numerous examples of fossil �fungi� which have no claim to be classed with plants, there are some whichnbsp;are in all probability the galleries of wood-eating animals.nbsp;The radiating grooves frequently found on the inner face ofnbsp;the bark of a pine tree made by species of the beetle Bostrychtisnbsp;might be mistaken for the impressions of the firm strands ofnbsp;mycelial tissue of some Basidiomycetous fungus.

In some notes on fossil fungi by J. F. James* contributed to the American Journal of Mycology in 1893, it is pointednbsp;out that a supposed fungus described by Lesquereux from the

1 For figures of the Coccineae, see Comstock (88), Maskell (87), Judeich and Nitsche (95) amp;c.

Lower Coal-Measures as Rhizomorpha Sigillariae^, bears a strong likeness to some insect-burrows, such as those of Bostrychus.

�A new fungus from the Coal-Measures� described by Herzer in 1893^ may probably be referred to animal agency.nbsp;In any case there is no evidence as to the fungoid nature ofnbsp;the object represented in the figure accompanying Herzer�snbsp;description.

More trustworthy evidence of fossil fungi is afforded by the marks of disease in petrified tissue and by thenbsp;presence of true mycelia. In examining closely the calcareousnbsp;and siliceous plant-tissues from the Coal-Measures andnbsp;other geological horizons, one occasionally sees fine threadlike hyphae ramifying through the cells or tracheal cavities ;nbsp;in many cases the hyphae bear no reproductive organs andnbsp;cannot as a rule be referred to a particular type of fungus.nbsp;If the hyphal filaments are unseptate, they most likelynbsp;belong to some Phycomycetous species; or if they are obviouslynbsp;septate the Mesomycetes or the Mycomycetes are the morenbsp;probable groups. Occasionally there may be found indicationsnbsp;of the characteristic clamp-connections in the septate filaments;nbsp;a small semicircular branch, which is given off from a myceliumnbsp;immediately above a transverse wall, bends round to fuse withnbsp;the filament just below the septum, thus serving as a smallnbsp;loop-line connecting the cell-cavity above and below a cross wall.nbsp;Such clamp-connections are usually confined to th� hyphaenbsp;of Basidiomycetes and thus serve as a useful aid in identification. A good example of a clamp-connection in a fossilnbsp;mycelium is figured by Conwentz� in his monograph on thenbsp;Baltic amber-trees of Oligocene age. The stout and thick typenbsp;of hypha found in some fossil woods agrees closely with thatnbsp;of Polyporus, Agaricus melleus and other well-known recentnbsp;Basidiomycetes.

In a section of a piece of lignified coniferous wood recently brought by Col. Feilden from Kolguev island ^ the brown and

1 Lesquereux (87). nbsp;nbsp;nbsp;^ Herzer (93).nbsp;nbsp;nbsp;nbsp;^ Conwentz (90) PL xii. fig. 5.

indebted to Dr Bonney for an opportunity of examining the plant remains from the Feilden collection.

stout hyphae of a fungus are clearly seen as distinct dark lines traversing the tracheal tissue. The occurrence of septa andnbsp;the large diameter of the mycelial branches at once suggestnbsp;a comparison with such recent forms as Agaricus melleus,nbsp;Polyporus and other Basidiomycetes. The age of the Kolguevnbsp;wood is not known with any certainty.

The vesicular swellings such as those represented in fig. 41, A, B, D and E, may easily be misinterpreted. Such sphericalnbsp;expansions in a mycelium, either terminal or intercalary, maynbsp;be sporangia, oogonia or large resting-spores, or non-fungal cell-contents, and it is usually impossible in the absence of thenbsp;contents to determine their precise nature. Hartig^ and othersnbsp;have drawn attention to the occurrence of such bladder-likenbsp;swellings in the mycelia of recent fungi, which have nothingnbsp;to do with reproductive purposes; under certain conditionsnbsp;the hyphae of a fungus growing in the cavity of a cell ornbsp;trachea may form such vesicles, and these, as in fig. 42, D,nbsp;m may completely fill up the cavity of a large tracheid.

Some good examples of bladder-like swellings, such as occur in the mycelium of Agaricus melleus and other recent fungi,nbsp;have been figured by Conwentz* in fossil wood of Tertiary agenbsp;from Karlsdorf. The swellings in this fossil fungus might easilynbsp;be mistaken for oogonia or sporangia; especially as they arenbsp;few in number and spherical in form.

A similar appearance is presented by a mass of tyloses in the cavity of an old vessel or tracheid; and vesicular cell-contents, as in the cells of fig. 41, A, 2-5, may closely simulatenbsp;a number of thin-walled fungal spores or sporangia.

A good example of such a vesicular tissue, in addition to that already quoted, is afforded by a specimen of an Eocenenbsp;fern, Osmundites Dovjkeri Carr.� described by Carruthers innbsp;1870. The ground-tissue cells contain traces of distinct fungalnbsp;hyphae (fig. 41, B), and in many of the parenchymatous elementsnbsp;the cavity is completely filled with spherical vesicles; in othernbsp;cases one finds hyphae in the centre of the cell while vesiclesnbsp;line the wall, as shewn in fig. 41, B. Carruthers refers to these

bladders as starch grains, and this may be their true nature; their appearance and abundant occurrence in the parenchymanbsp;certainly suggest vesicular cell-contents rather than fungalnbsp;cells. I could detect no proof of any connection between thenbsp;hyphae and bladders, and the absence of the latter in thenbsp;cavities of the tracheids, fig. 41, C, favoured the view of theirnbsp;being either starch-grains or other vacuolated contents similarnbsp;to that in the cells of the Portland Cycad (fig. 41, A) referrednbsp;to on p. 88.

The vacuolated cell-contents partially filling the cells in fig. 41, D, present a striking resemblance to the contents of thenbsp;cells 2-5 in fig. 41, A. In fig. D the frothy and contractednbsp;substance might be easily mistaken for a parasitic or saprophytic fungus, but this resemblance is entirely misleading. Itnbsp;is by no means uncommon to find the cells of recent plantsnbsp;occupied by such vacuolated contents, especially in diseasednbsp;tissues in which a pathological effect produces an appearancenbsp;which has more than once misled the most practised observers.

In the important work recently published by Renault on the Permo-Carboniferous flora of Autun, there is a small sporelike body described as a teleutospore, and classed with thenbsp;Puccineaeh We have as yet no satisfactory evidence of thenbsp;existence of this section of Fungi in Palaeozoic times, andnbsp;Renault�s description of Teleiitospora Milloti from Autun mightnbsp;be seriously misleading if accepted without reference to hisnbsp;figure. The fragment he describes cannot be accepted asnbsp;sufficient evidence for the existence of a Palaeozoic Puccinia.

The same author refers another Palaeozoic fungus to the Mucorineae under the name of Mucor Combrensis^; this identification is based on a mycelium having a resemblance tonbsp;the branched thallus of Mucor, but in the absence of reproductive organs such resemblance is hardl}^ adequate as a meansnbsp;of recognition.

The occurrence of hyphal cells in calcareous shells and corals has already been alluded to.� In addition to thenbsp;examples referred to above, there is one which has been

Fig. 41. A. Cells of Cycadeoidea gigantea Sew. x 355. B and C. Parenchymatous cells and scalariform tracheids of Osmundites VotcTteri Carr, x 230.

D. nbsp;nbsp;nbsp;Epidermal cells of Memecylon (Me.lastomaceae) with vacuolated contents.

E. nbsp;nbsp;nbsp;Peronosporites antiquarius Smith, (No. 1923 in the Williamson collection).

X 230. P. Zygosporites. x 230. nbsp;nbsp;nbsp;(A, B, C and E drawn from specimens

in the British Museum; D from a drawing by Prof. Marshall Ward; E from a specimen in the Botanical Laboratory Collection, Cambridge.)

described by Etheridge� from a Permo-Carboniferous coral. This observer records the occurrence of tubular cavities in thenbsp;calices of Stenopora crinita Lonsd., and attributes their originnbsp;to a fungus which he names Palaeoperone endophytica; henbsp;mentions one case in which a tube contains fine sphericalnbsp;spore-like bodies which he compares with the spores of anbsp;Saprolegnia. As pointed out above (p. 128), it is almostnbsp;impossible to decide how far these tubes in shells and coralsnbsp;should be attributed to fungi, and how far to algae.

A nbsp;nbsp;nbsp;E

Fig. 42. A, B, C. Tracheids of coniferous wood attacked by Trametes radiciperda Hart. {Polyporus aniiosus Fr.) D and E. Tracheids attacked by Agaricusnbsp;melleus Vahl. A, x650, B�E, x 360. (After Hartig.)

Passing from the direct evidence obtained from the presence of fungal hyphae in petrified tissues, we must draw attentionnbsp;to the indirect evidence of fungal action afforded by manynbsp;fossil plants. It is important to be familiar with at least thenbsp;more striking effects of fungal ravages in recent wood in ordernbsp;that we may escape some of the mistakes to which pathologicalnbsp;phenomena may lead us in the case of fossils�.

fossil wood owing to the destruction of the middle lamellae, the occurrence of various forms of slit-like apertures in thenbsp;walls of tracheids (fig. 42, E) and the production of a system ofnbsp;fine parallel striation on the walls of a vessel are among thenbsp;results produced by parasitic and saprophytic fungi. Withnbsp;the help of a ferment secreted by its hyphae, a fungus is ablenbsp;to eat away either the thickening cell layers or the middlenbsp;lamellae or both, and if, as in fig. 42, A, only the middlenbsp;lamellae are left one might easily regard such tissue in anbsp;fossil condition as consisting of delicate thin-walled elements.nbsp;The oblique striae on the walls of a tracheid may often be duenbsp;to the action of a ferment which has dissolved the membranenbsp;in such a manner as to etch out a system of spiral lines, probablynbsp;as a consequence of the original structure of the tracheids. Innbsp;distinguishing between the woods of Conifers the presence ofnbsp;spiral thickening layers in the wood element is an importantnbsp;diagnostic character, and it is necessary to guard against thenbsp;confusion of purely secondary structures, due to fungal action,nbsp;with original features which may be of value in determiningnbsp;the generic affinity of a piece of fossil wood.

Oochytrium Lepidodendri, Ren. Fig. 43, 1. Under this name Renault has recently described a filamentous fungus endophyticnbsp;in the cavities of the scalariform tracheids of a Lepidodendron^.nbsp;The mycelium has the form of slender branched hyphae withnbsp;transverse septa. Numerous ovoid and more or less sphericalnbsp;sporangia occur as terminal swellings of the mycelial threads.nbsp;The long axis of the ovoid forms measures 12�15 p,, and thenbsp;shorter axis 9�10 /r; the contents may be seen as a slightlynbsp;contracted mass in the sporangial cavity. In some of thenbsp;sporangia one sees a short apical prolongation in the form ofnbsp;a small elongated papilla, as shown in fig. 43, 1. Renaultnbsp;refers this fungus to the Chytridineae, and compares it withnbsp;Cladochytrivm, Woronina, Olpidium, and other recent genera.

In the immediate neighbourhood of two of the sporangia shown in the uppermost tracheid of fig. 43, 1, there are seen anbsp;few minute dark dots which are described as spores petrified

in the act of escaping from a lateral pore. This interpretation strikes one as lacking in scientific caution.

The sporangia of Hyphochytrium infestans^, as figured by Fischer in Rabenhorst�s work bear a close resemblance to thosenbsp;of the fossil. It would seem very probable that Renault�snbsp;species may be reasonably referred to the Chytridineae, asnbsp;he proposes.

lt;P

F10. 43. nbsp;nbsp;nbsp;1. Oochytrium Lepidodendri, Een. (After Eenault.) 2. Polyporus

vaporarius Fr. var. succinea. (After Conwentz.) 3. Cladosporites bipar-titus Fel. (After Felix.) 4. Haplographites cateniger Fel. (After Felix.)

In an address to the Geologists� Association delivered by Mr Carruthers in 1876 a brief reference, accompanied by anbsp;small-scale drawing, is made to the discovery of a fungus in thenbsp;scalariform tracheids of a Lepidodendron from the Englishnbsp;Coal-Measures^. In the following year Worthington Smithnbsp;published a fuller account of the fungus, and proposed fornbsp;it the above name�, which he chose on the ground of anbsp;close similarity between the mycelium and reproductivenbsp;organs of the fossil form and recent members of the

2 nbsp;nbsp;nbsp;Carruthers (76) p. 22, fig. 1.nbsp;nbsp;nbsp;nbsp;� Smith, W. G. (77) p. 499.

Peronosporeae. In Smith�s description the m3fcelium is described as bearing spherical swellings containing zoospores. These spherical organs are fairly abundant and not infrequentlynbsp;met with in sections of petrified plant-tissues from the Englishnbsp;Coal-Measures; they may be oogonia or sporangia, or innbsp;some cases mere vesicular expansions of a purely vegetativenbsp;hypha. No confirmation has been given to the supposed sporesnbsp;referred to by Smith. Prof. Williamson and others have carefully examined the specimens, but they have failed to detectnbsp;any trace of reproductive cells enclosed in the spherical sacsbnbsp;The mycelium does not appear to show any satisfact02�ynbsp;evidence of its being septate as figured by Smith.

The example shown in fig. 41 E has been drawn from one of the Williamson specimens: it illustrates the form andnbsp;manner of occurrence of the characteristic swellings. It isnbsp;probable that some at least of the vesicles are either sporangianbsp;or oogonia, but we cannot speak with absolute confidence as tonbsp;their precise nature. The general habit and structure of thenbsp;fungus favour its inclusion in the class of Phycomycetes. Thenbsp;occurrence of several of the vesicles close together on shortnbsp;hyphal branches, as shown in Williamson�s figures, suggests thenbsp;spherical swellings on vegetative hyphae, but it is impossible tonbsp;speak with absolute confidence. There is a close resemblancenbsp;between this English form and one recently described bynbsp;Renault as Palaeomyces gracilis Ren.^; the two fossils shouldnbsp;probably be placed in the same genus.

The examples referred to below and originally recorded by Cash and Hick no doubt belong to the same type as Smith�snbsp;Peronosporites.

The sketches reproduced in fig. 44 have been drawn from specimens originally described by Cash and Hick in 1878bnbsp;The sections were cut from a calcareous nodule from thenbsp;Halifax Coal-Measures containing fragments of various plantsnbsp;and among others a piece of cortical tissue, probably of anbsp;* Lepidodendron or Stigmaria. In a transverse section of this

destruction of the middle lamella (fig. 44 A). The cell-cavities and the spaces between the isolated cells contain numerous fine fungal hyphae, which here and there terminatenbsp;in spherical swellings. One such swelling is shown under a lownbsp;power in fig. 44 A, in the middle uppermost cell, and morenbsp;highly magnified in fig. 44 B. In fig. C there are two suchnbsp;swellings (the larger one having a diameter of '003 mm.) innbsp;contact, hut the connection does not appear to be organic.nbsp;The cell-walls of the infected tissue present a ragged andnbsp;untidy appearance, and in places {e.g. fig. 44 D) the membranenbsp;has been pierced by some of the mycelial branches.

This fungus bears a close resemblance to Peronosporites antiquarius, but it is impossible to determine its precisenbsp;botanical position without further data. In Cash and Hick�snbsp;paper in which the above fungus is briefly dealt with, some

small spore-like bodies are figured which the authors speak of as possibly a Myxoinycetous fungus^. There is however nonbsp;sound reason for such a supposition.

As examples of Ascomycetous fungi found in silicified wood of Tertiary age, two species may be quoted from Felix.

Cladosporites bipartitus Felix fig. 43, 3. The mycelium and conidia of this form were discovered in some Eocene silicified wood from Perekeschkul near Baku, on the shores of thenbsp;Caspian. The conidia are elliptical or pyriform in shape andnbsp;divided by a transverse septum into two cells. No traces werenbsp;found of any special conidiophores. The mycelium consists ofnbsp;septate branched hyphae, rendered conspicuous by a brownnbsp;colouration. Felix compares the fossil with the recent generanbsp;Cephalothecium and Gladosporium.

Haptographit�s canteniger Felix^, fig. 43, 4. The conidia of this form were found to be fairly abundant in the silicifiednbsp;tissue investigated by Felix; they occur usually in chains of 2nbsp;to 6 conidia having an ovoid or flask-shaped form, with a thicknbsp;membrane (fig. 43, 4). The mycelium consists of branchednbsp;hyphae divided into long cylindrical cells by transverse septa;nbsp;occasional instances were found of an H-shaped fusion betweennbsp;lateral branches of parallel hyphae.

Felix compares this species with examples of the genera Haptographium and Dematium of the family Sphaeriaceae;nbsp;it was found in the woody tissue of a dicotyledonous stem fromnbsp;Perekeschkul.

Zygosporites sp. The object represented in fig. 41 F consists of a stalked spherical sac bearing a number of radiatingnbsp;arms which are divided distally into delicate terminations.nbsp;We find similar bodies figured by Williamsonquot;* in his IXthnbsp;and Xth Memoirs on the Coal-Measure plants; he includesnbsp;some of them under the generic term Zygosporites, and

compares them with the zygospores of the freshwater algae Desmideae. Hitherto these spore-like fossils have only beennbsp;recorded as isolated spheres, but in the example shown innbsp;fig. 41 F there is a distinct tubular and thin-walled stalknbsp;attached to the Zygosporites. The specimen was found in thenbsp;partially disorganised cortical tissue of a Lyginodendron stemnbsp;from the English Coal-Measures. It is difficult to decide as tonbsp;the precise nature of the fossil, but the presence of the hyphalnbsp;stalk points to a fungus rather than an alga as the mostnbsp;probable type of plant with which to connect it. It maynbsp;possibly be a sporangium of a fungus comparable with thenbsp;common mould Mucor, or it may be a zygospore formed bynbsp;the conjugation of two hyphae of which only one has beennbsp;preserved.

For an example of a fossil representative of the Basidiomy-cetes we may turn to the excellent monograph by Conwentz on the Baltic amber trees, and quote one of the forms which henbsp;has described.

Polyporus vaporarius Fr. swccfnea*, fig. 43, 2. In several preparations of the wood preserved by petrifaction in amber ^nbsp;Conwentz found distinct indications of the ravages of a fungus,nbsp;which suggested the presence of the recent species Poly-porus vaporarius Fr. With the help of the indirect evidencenbsp;afforded by the pathological effects as seen in the tissues ofnbsp;the host-plant, and the direct evidence of the fungal myceliumnbsp;Conwentz was led to this identification.

The mycelium is brown in colour, in part thick-walled, and in part with thin walls, transversely septate and not muchnbsp;branched. In the portion of one of Conwentz� figures reproduced in fig. 43, 2, the rents and holes in the tracheid wallsnbsp;are clearly shown; they afford the indirect evidence of fungalnbsp;attacks, and are of the same nature as those shown in fig. 42,

Enough has been said to call attention to the paucity of exact data on which to generalise as to the geological history

of fungi. The types selected for description or passing allusion have not been chosen in each case because of their specialnbsp;intrinsic value, but rather as convenient examples by which tonbsp;illustrate authentic records or to serve as warnings againstnbsp;possible sources of error.

It would seem that we have fairly good and conclusive evidence of the existence in Permo-Carboniferous times ofnbsp;Phycomycetous fungi, but it is not until we pass to post-Palaeozoic or even Tertiary plants that we discover satisfactorynbsp;representatives of the higher fungi or Mycomycetes. If specialnbsp;attention were paid to the investigation of fossil fungi, it isnbsp;quite possible that our knowledge of the past history of thenbsp;group might be considerably extended. It is essential thatnbsp;the greatest caution should be exercised in the identificationnbsp;of forms and in their reference to definite families; otherwisenbsp;our lists of fossil species will serve to mislead, and to emphasizenbsp;the untrustworthy character of palaeobotanical data. Unlessnbsp;we feel satisfied as to the position of a fossil fungus it is unwisenbsp;to use a generic term suggestive of a definite family or recentnbsp;genus. Such a name as Renault has used in one instance,nbsp;Palaeomyces, might be employed as a useful and comprehensivenbsp;designation.

VII. CHAROPHYTA.

CHAEACE^. NITELLEtE.

It has been the general custom to include the Characeas or Stoneworts among the Chlorophycese (green algae), of whichnbsp;they form a distinctly isolated family. On the whole, it wouldnbsp;seem better to follow the course lately adopted by Migula^ andnbsp;allow the Characese to rank as a family of a distinct group,nbsp;Charophyta. While agreeing in many respects with plantsnbsp;higher in the scale than Thallophytes, the Stoneworts do notnbsp;sufficiently resemble the Bryophyta to be included in thatnbsp;group.

The Charophyta are plants containing chlorophyll, living in fresh and brackish water; the stem is jointed, and hears at thenbsp;nodes whorls of leaves, on which are borne the reproductivenbsp;organs. The antheridia are spherical in shape and of complexnbsp;structure, containing numerous biciliate antherozoids. Thenbsp;oogonia are oval in form and contain a single large egg-cell.nbsp;The Chara-plant is developed from a protonema formed fromnbsp;the germinating oospore. Vegetative reproduction is effectednbsp;by means of bulbils, accessory shoots, etc.

The Nitellese have not been recognised in a fossil condition. The absence or feeble development of a calcareous incrustationnbsp;renders the genera of this family less likely to be preservednbsp;than such a genus as Ghara.

Leaves and stems with or without a cortical investment. Fruit with a five-celled corona. The envelope of the � fruit �nbsp;and other parts of the plant are frequently encrusted withnbsp;carbonate of lime.

In the genus Ghara, the best known member of the family, the plant as a whole resembles in its general habit and externalnbsp;differentiation of parts the higher plants. The stem consistsnbsp;of long internodes separated by short nodes bearing whorls ofnbsp;leaves. Each internode consists of a long cylindrical cell, whichnbsp;becomes enclosed by a cortical sheath composed of rows of cellsnbsp;which have grown upwards and downwards from the peripheralnbsp;nodal cells. The cortical cells are usually spirally twisted andnbsp;impart to the stem a characteristic appearance ; they are dividednbsp;by transverse walls into numerous cells some of which occasionally grow out into short processes (fig. 45 c). The leaves repeatnbsp;on a smaller scale the structural features of the stem, butnbsp;possess a limited growth, whereas the stem has an unlimitednbsp;power of growth by means of a large hemispherical apical cell.nbsp;Branches arise in the axils of the leaves. The plants are eithernbsp;monoecious or dioecious. The oogonium is elliptical in shape,nbsp;and is borne on a short stalk-cell, it contains a single oosphere.nbsp;The wall of the oogonium is formed of five spirally twisted cellsnbsp;which have grown over it from the five peripheral cells of a

leaf-node. The tips of the investing cells project at the apex in the form of a terminal crown or corona (fig. 45, E, c). Thenbsp;antheridia have a complex structure, and produce a very largenbsp;number of motile antherozoids.

After fertilisation, the egg-cell becomes surrounded by a membrane, at first colourless, but afterwards yellow or brown.nbsp;The inner cell-walls of the cells surrounding the oospore becomenbsp;thicker and darker in colour; the outer walls remain thin andnbsp;eventually fall away. The lateral walls may or may notnbsp;become thickened. In most of the Chareae a calcareous depositnbsp;is formed between the hard shell and the outer walls of thenbsp;cells enveloping the oospore. This calcareous shell is developednbsp;subsequently to the thickening and hardening of the inner

walls of the fruit-case. The cells of the corona and stalk do not become calcareous. In the fossil Charas, it is this calcareousnbsp;shell that is preserved. In the members of the Chareae thenbsp;stems are usually encrusted with carbonate of lime, and thusnbsp;have a much better chance of preservation than the slightlynbsp;calcareous Nitelleae.

The generic characters have already been described in the brief account of the family Chareae.

The generic name was proposed by Vaillant in I7l9h and adopted by Linnaeus, who classed the Stoneworts with aquaticnbsp;phanerogams. As long ago as 1623^ a figure of Ghara wasnbsp;published by Caspar Bauhin as a form of Equisetum. Thenbsp;generic name Ghara has usually been applied to recent andnbsp;fossil species alike. The existing species have a wide distribution ; Chara foetida, A. Br., a common British form, occursnbsp;in practically all parts of the world. Stems and calcareousnbsp;'fruit-cases� occur fairly commonly in a fossil state, and differnbsp;but little from recent species, at least as regards essentialnbsp;features.

It is difficult to say at what geological horizon the Stone-worts are first represented. The first certain traces of Chara occur in Jurassic rocks, but certain spirally marked subsphericalnbsp;bodies have been recorded from Devonian and Carboniferousnbsp;strata, which closely resemble Chara oogonia, and may benbsp;Palaeozoic representatives of the genus.

In 1889 Mr Knowlton� of the American Geological Survey described some � problematic organisms � found in Devoniannbsp;rocks at the falls of the Ohio. Examples of these fossils arenbsp;shown in fig. 46 b and c; the spirally grooved body measui'esnbsp;from I'SO to 1�80 mm. in diameter, and about 1�70 mm. innbsp;length. The Chara-like character of the fossils had beennbsp;previously suggested by Meek^ in 1873. Without going intonbsp;the arguments for or against placing these fossils in the Chareae,

they may at least be mentioned as possible but not certain Palaeozoic forms of Ohara or an allied genus.

1. nbsp;nbsp;nbsp;Ohara Bleicheri, Saporta. Fig. 46, a. In this form thenbsp;�fruits� are minute and subspherical, '39��44mm. long, andnbsp;'35�'40 mm. broad, showing in side view 5�6 slightly obliquenbsp;spiral bands. Each spiral band bears a row of slightly projecting tubercles.

This species was first described by Saporta^ from the Oxfordian (Jurassic) rocks of the Department of Lot in France ;nbsp;it is compared by the author of the species with Ohara Jaccardinbsp;Heer, described by Heer from the Upper Jurassic rocks ofnbsp;Switzerland.

2. nbsp;nbsp;nbsp;0. Knowltoni, Seward. Fig. 45, a and b, and Fig. 47.nbsp;The Oogonia are broadly oval, about '5 mm. in length, and at thenbsp;broadest part of about the same breadth. The surface isnbsp;marked by eleven or twelve bands in the form of a flattenednbsp;spiral. The stems possess investing cortical cells.

This species was founded on specimens from the �Wealden beds of Sussex^, but numerous examples of Chara �fruits� andnbsp;stems have long been known from the uppermost Jurassicnbsp;rocks of the Dorset coast and the Isle of Wight, which maynbsp;probably be included in this species. These fossil Charas are

abundant^ in the Chert beds of Purbeck age seen in the cliffs near Swanage. Pieces of corticated stems from this locality arenbsp;represented in fig. 45 A and B.

The cortical cells surrounding a large internodal cell are very clearly seen in the section shown in fig. 45 B, and in thenbsp;longitudinal view in fig. 45 A. The resemblance of thesenbsp;specimens to the stems of recent Stoneworts is very striking.

3. Chara Wrighti, Forbes. Fig. 46, d and e. This species is characterised by globular or somewhat elliptical oogonia, withnbsp;six or seven spiral bands.nbsp;nbsp;nbsp;nbsp;lt;

It is very abundant in the Lower Headon beds of Hordwell Cliffs on the Hampshire coast^. Various species ofnbsp;Chara are commonly met with in the Oligocene beds of thenbsp;Isle of Wight and Hampshire, as well as in the Paris basinnbsp;beds, and elsewhere. Well preserved �fruits� and stem fragments are met with in a siliceous rock of Upper Oligocene agenbsp;imported from Montmorency in the Paris basin, and used as anbsp;stone for grinding phosphates at some chemical works nearnbsp;Upware, a few miles from Cambridge.

Many other species of fossil Charas are known from various horizons and localities, but the above examples suffice asnbsp;illustrative types. In Post-Tertiary deposits masses of Charanbsp;and plant fragments occasionally occur forming blocks ofnbsp;Travertine. Examples of such Chara beds have been recordednbsp;by Sharpe from Northampton�, by LyelP from Forfarshire, and

by other writers from several other districts. Beds of calcareous marl are occasionally seen as whitish streaks in the peatnbsp;of the Fenland'; these often consist in great part of Oharas.nbsp;A season�s growth of Chara in a shallow lake or mere in thenbsp;Fens may appear as a white line in a section of peaty and othernbsp;material which has been formed on the site of old pools ornbsp;lakes.

The recognition of specific characters in the isolated Chara �fruits� usually met with in a fossil state is exceedingly unsatisfactory ; the features usually relied on in the living speciesnbsp;are not preserved, and great care should be taken in the separation of the various forms.

CHAPTEK VIII.

The Bryophyta are small plants, varying in size from 1 mm. to about 30 cm., creeping or erect, having a thalloid, or morenbsp;usually a foliose body, consisting of a cell-mass exhibiting innbsp;most cases a distinct internal differentiation. They possess nonbsp;true roots and no true vascular tissue. The life-history of thenbsp;members of the group is characterised by a well-marked andnbsp;definite alternation of generations. The Moss or Liverwortnbsp;plant is the sexual generation (gametophyte), and as a resultnbsp;of the fertilisation of an egg-cell the asexual or spore-bearingnbsp;generation (sporophyte) is produced. The sporophyte nevernbsp;exhibits a differentiation into stem and leaves. Asexual andnbsp;vegetative reproduction are effected by means of spores, bulbils,nbsp;or detached portions of the plant-body. Sexual reproductionnbsp;is by means of biciliate antherozoids produced in antheridia andnbsp;egg-cells formed singly in archegonia.

In the Bryophytes the distinguishing characteristics are more constant and well-defined than in the Thallophytes, Innbsp;the former the plant never consists of a single cell or coenocyte,nbsp;out is always multicellular, and exhibits in most cases anbsp;definite physiological division of labour as expressed in thenbsp;histological differentiation of distinct tissue-systems. In thenbsp;Thallophytes there is no true alternation of generation innbsp;the same sense as in the Mosses and Liverworts and in thenbsp;higher plants. In the Bryophyt es the sexual reproduction hasnbsp;reached a higher stage of development and a much greaternbsp;constancy as regards the nature of the reproductive organs.

On the germination of the spore there is usually formed a fairly distinct structure known as the protonema, from which thenbsp;Moss or Liverwort developes as a hudh

The vegetative plant-body possesses a different organisation on the ventral and dorsal side ; it has the form of a thalloidnbsp;creeping plant (Thalloid Liverworts), or of a delicate stem withnbsp;thin appendages or leaves without a midrib (Foliose Liverworts). In most cases the body of the plant is made up ofnbsp;parenchymatous tissue, showing but little internal differentiation ; in one or two genera a few strengthening or mechanicalnbsp;fibres occur among the thinner walled ground-tissue. On thenbsp;germination of the spore, a feebly developed protonema isnbsp;produced, which gives rise to the Liverwort plant. Reproduction as in the group Bryophyta.

The Liverworts have a very wide geographical distribution, and are specially abundant in moist shady situations; theynbsp;grow on stones or damp soil, and occur as epiphytes on othernbsp;plants. Marchantia, Pellia, and Jungermannia are anjong thenbsp;better known British representatives of the class.

Considering the soft nature of the body of recent Liverworts, it is not surprising that they are poorly represented in a fossil state. In the absence of the sexual reproductive organs,nbsp;or of the sporophytes, which have scarcely ever been preserved,nbsp;exact identification is almost hopeless. The difficulties alreadynbsp;referred to in dealing with the algae, as regards the misleadingnbsp;similarity between the form of the thallus and the bodies ofnbsp;other plants, have to be faced in the case of the Liverworts.nbsp;Many of the thalloid Liverworts, if preserved in the form of anbsp;cast or impression without internal structure or reproductivenbsp;organs, could hardly be distinguished from various genera ofnbsp;algae in which the thallus has the form of a forked plate-like

1 Schiffner and Miiller in Bngler and Prantl (95), Campbell (95), Dixon and Jameson (96) are among the best of modern writers on the Bryophyta.

body. Such genera as Pellia, Marchantia, Lunularia, Reboulia, and others bear a striking resemblance to Fucus, Chondrus andnbsp;many other algae.

Imperfect specimens of certain Lichens, not to mention some of the Polyzoa, might easily be mistaken for Liverworts.nbsp;Among the higher plants, there are some forms of the Podo-stemaceae which simulate in habit both thalloid and foliosenbsp;Liverworts as well as Mosses k The members of this Dicotyledonous family are described as water-plants with a Moss- ornbsp;Liverwort-like form; they occur on rocks in quickly-flowingnbsp;water in the tropics. In one instance a recent Podostemaceousnbsp;genus has been described as a member of the Anthocerotales;nbsp;the genus Blandowia^, referred to by Willdenow as a Liverwort,nbsp;has since been recognised as one of the Podostemaceae. Thenbsp;resemblance between some of the foliose Hepaticae and generanbsp;of Mosses is often very close. In certain Mosses, such asnbsp;Hookeria pennata^, the large two-ranked leaves suggest thenbsp;branches of a Selaginella.

The plant reproduced in fig. 48 A (Tristichia), one of the Podostemaceae, might easily be mistaken for a foliose Liverwortnbsp;if found as a fragmentary fossil. Such species of Selaginellanbsp;as S. Oregana Eat. and 8. rupestris Spring (fig. 48 C) have anbsp;distinctly moss-like habit and do not present a very obviousnbsp;resemblance to the more typical and better known Selaginellas.nbsp;The twig of a Podocarpus (P. cupressinaY in fig. 48 B affordsnbsp;an instance of a conifer which simulates to some extent certainnbsp;of the larger-leaved Liverworts; it bears a resemblance also tonbsp;some fossil fragments referred to Selaginellites or Lycopodites.nbsp;A small fossil specimen figured by Nathorst*� from Japan asnbsp;possibly a Lycopodites may be compared with a coniferous twig,nbsp;and with some of the larger Liverworts, e.g. species of PlagiochiW.nbsp;Podocarpus cupressina is, however, chiefly instructive as annbsp;example of the striking differences which are met with amongnbsp;species of the same genus; it differs considerably from thenbsp;ordinary species of Podocarpus, and might well be identifiednbsp;as a member of some other group than that of the Coniferae.

We have no records of Palaeozoic Hepaticae. The fossils which Zeiller has figured in his Flore de Brive as Schizopterisnbsp;dichotoma Gumb.^ and 8. trichomanoides G�pp. bear a resemblance to some forms of hepatics, but there is no satisfactorynbsp;evidence for removing them from the position assigned to themnbsp;by the French writer. In Mesozoic rocks a few specimens arenbsp;known which bear a close resemblance as regards the form of thenbsp;thalloid body to recent Liverworts, but the identification of suchnbsp;fossils cannot be absolutely trusted. Two French authors,nbsp;MM. Fliche and Bleicher�, have described a plant from Lowernbsp;Oolite rocks near Nancy as a species of Marchantia, M. oolithius,nbsp;but they point out the close agreement of such forked laminarnbsp;structures to algae and lichens. From Tertiary and Post-Tertiary beds a certain number of fossil species have beennbsp;recorded, but they possess no special botanical interest.

The plant-body is always thalloid, hearing rhizoids on the* lower surface, and having an epidermis with pores limiting thenbsp;upper or dorsal surface.

This convenient generic name was proposed by Brongniart in 1849^; it may be briefly defined as follows:

Vegetative body of laminar form, with apparently dichotomous branches, and agreeing in habit with the recent thalloid Hepaticae, as represented by such a genus as Marchantia.

The name Marchantites is preferable to Marchantia, as the latter implies identity with the recent genus, whereas thenbsp;former is used in a wide sense and refers rather to a definitenbsp;form of vegetative body than to a particular generic type.

1. Marchantites erectus (Leckenby). Fig. 49. This species may be described as follows: The thalloid body is divided intonbsp;spreading dichotomously branched segments, obtusely pointednbsp;apically. The slightly wrinkled surface shows a distinct andnbsp;comparatively broad darker and shorter median band, withnbsp;lighter coloured and thinner margins.

In 1864 Leckenby described this plant from the Lower Oolite beds of the Yorkshire coast near Scarborough, as Fucoidesnbsp;erectus, regarding it as a fossil alga. I recently pointed out

that the general appearance and mode of occurrence of the specimens suggest a liverwort rather than an alga, and proposednbsp;^h e substitution of the genus Marchantites^. It would, however,nbsp;be unwise to speak with any great confidence as to the realnbsp;affinities of the fossil.

The example shown in the figure is the type-specimen of Leckenby^; the breadth of the branches is about 3 mm.nbsp;Under a low magnifying power the surface shows distinct andnbsp;somewhat oblique wrinklings, the general appearance being verynbsp;similar to that of some recent forms of the genus Marchantia.

A closely allied species has recently been described from the Wealden beds of Ecclesbourne, near Hastings, on thenbsp;Sussex coast, as Marchantites Zeilleri Sew.'�.

In a recent monograph on Jurassic plants from Poland, apparently containing much that is of the greatest value, butnbsp;which is unfortunately written in the Polish language, Raci-borski^ describes a new species of thalloid Liverwort under thenbsp;name of Paleohepatica Rostafinshi. The specimens are barrennbsp;plants larger than any Jurassic species hitherto described ; theynbsp;agree closely in habit with Saporta�s Tertiary species Marchantites Sezannensis.

2. Marchantites Sezannensis Saporta. Fig. 50. The body is broadly linear and dichotomously branched, with a somewhatnbsp;undulating margin. Midrib on the dorsal surface depressed, butnbsp;more prominent on the ventral surface. The upper surface isnbsp;divided into hexagonal areas, in each of which occurs a centralnbsp;pore. There are two rows of scales along the median line onnbsp;the lower surface. Stalked male receptacles.

Brongniart� first mentioned this fossil hepatic, which was found in the calcareous travertine of Sezanne of Oligocene agenbsp;in the Province of Marne. The specimens figured by Saporta'^nbsp;show very clearly the characters of one of the Marchantiaceae,

and in this case we have the additional evidence of the characteristic male receptacles which are given off from a point towards the apex of the lobes, and arise from a slight median

depression. Iti one of Saporta�s figures (reproduced in fig. 50 A) there are represented some median scars which may mark thenbsp;position of cups similar to those which occur on recent speciesnbsp;of Marchantia, and in which gemmae or bulbils are produced.

The collection of S�zanne fossils in the Sorbonne includes some very beautiful casts of Marchantites in which thenbsp;structural details are preserved much more perfectly than innbsp;the examples described by Saporta. In a few specimens whichnbsp;Prof Munier-Chalmas recently showed me the reproductivenbsp;branches were exceedingly well shown. The fossils occur asnbsp;moulds in the travertine, and the museum specimens are in thenbsp;form of plaster-casts taken from the natural moulds.

Several species of Liverworts belonging to the Marchantiales and Jungermanniales have been recorded from the amber ofnbsp;North Germany, of Oligocene age. These appear to be represented by small fragments, such as are figured by G�ppert and

Berendt^ in their monograph on the amber plants, published in 1845. The determinations have since been revised by Gottsche^,nbsp;who recognises species of Frullania, Jungermannia, and othernbsp;genera.

The plant-body (gametophyte) in the Musci consists of a stem bearing thin leaves, usually spirally disposed, rarely innbsp;two rows. The internal differentiation of the stem is generallynbsp;well marked, and in some cases is comparable in complexitynbsp;with the structure of the higher plants. A protonema arisesnbsp;from the spore, having the form of a branched filamentous,nbsp;or more rarely a thalloid structure. Reproduction as in thenbsp;group Bryophyta.

Mosses like Liverworts have an extremely wide distribution, and occur in various habitats. In many districts vast tractsnbsp;of country are practically monopolised by peat-forming genera,nbsp;such as Sphagnum and other Mosses. Some genera are foundnbsp;on rocks at high altitudes in dry regions, a few grow asnbsp;saprophytes, and many occur either as epiphytes on the leavesnbsp;and stems of other plants, of carpeting the ground under thenbsp;shade of forest trees.

In the simpler Mosses, the stem consists of a parenchymatous ground-tissue with a few outer layers of thicker-walled and smaller cells. In others there is a distinct central cylindernbsp;which occupies the axis of the stem, and consists of longnbsp;and narrow cells; in the more complex forms the structure ofnbsp;the axial tissues suggests the central cylinder or stele of highernbsp;plants. The genus Polytrichum, so abundant on English moors,nbsp;illustrates this higher type of stem differentiation. In anbsp;transverse section of the stem the peripheral tissue is seen to benbsp;composed of thick-walled cells, passing internally into largenbsp;parenchymatous tissue. The axial part is occupied by a

definite central cylinder consisting in the centre of elongated elements with dark-coloured and thick walls having thinnbsp;transverse septa; surrounding this central tissue there arenbsp;thinner walled elements, of which some closely agree in formnbsp;with the sieve-tubes of the higher plants. The central tissuenbsp;may be regarded as a rudimentary type of xylem, and thenbsp;surrounding tissue as a rudimentary phloem. Each leaf isnbsp;traversed by a median conducting strand which passes into thenbsp;stem and eventually becomes connected with the axial cylinder.

The fertilisation of the egg-cell gives rise to the development of a long slender stalk terminating distally in a large spore-capsule. In section the stalk or seta closely resembles thenbsp;leafy axis of the moss plant. Considering the fairly closenbsp;approach of some of the mosses to the higher plants as regardsnbsp;histological characters, it is conceivable that imperfectly petrified stems of fossil mosses might be mistaken for twigs ofnbsp;Vascular Cryptogams.

Like Liverworts, Mosses have left very few traces of their existence in plant-bearing rocks. Without the aid of_., thenbsp;characteristic moss-� fruit � or sporogonium it is almost impossible to recognise fossil moss-plant fragments. In species ofnbsp;the tropical genera Spiridens and Dawsonia, e.g. S. longi-foliiis^ Lind, or D. superha^ Grev. and D. polytrichoides^ R. Br.,nbsp;the plant reaches a considerable length, and resembles twigs ofnbsp;plants higher in the scale than the Bryophytes. The finernbsp;branches of species of the extinct genus Lepidodendron arenbsp;extremely moss-like in appearance. Again, Cyathophyllumnbsp;hulbosum MuelC, with its two kinds of leaves arranged in rows,nbsp;is not at all unlike species of Selaginella or the hepaticnbsp;genus Oottschea. It is by no means improbable that some ofnbsp;the Palaeozoic specimens described as twigs of Lycopodites,nbsp;Selaginites, or Lepidodendron, may be portions of mosses.nbsp;The fertile branches of Lycopodium phlegmaria in a fossilnbsp;condition might be easily mistaken for fragments of a moss.nbsp;In some conifers with small and crowded scale-leaves therenbsp;IS a certain resemblance to the stouter forms of moss stems.

Such possible sources of error should be prominently kept in view when we are considering the value of negative evidencenbsp;as regards the geological history of the Musci.

A recent writer ^ on mosses has expressed the opinion that no doubt the Musci played an exceedingly important r�le innbsp;past time. Although we have no proof that this was so, yetnbsp;it is far from improbable, and the absence of fossil mosses mustnbsp;no doubt be attributed in part to their failure to be preservednbsp;in a fossil state.

In the numerous samples of Coal-Measure vegetation preserved in extraordinary perfection in the calcareous nodules of England, no certain trace of a moss has so far beennbsp;discovered. The most delicate tissue in the larger Palaeozoicnbsp;plants has often been preserved, and in view of such possibilitiesnbsp;of petrifaction it might appear strange that if moss-like plantsnbsp;existed no fragments had been preserved. Their absence is,nbsp;however, no proof of the non-existence of Palaeozoic mosses,nbsp;but it is a fact which certainly tends towards the assumptionnbsp;that mosses were probably not very abundant in the Coalnbsp;Period forests. Epiphytic mosses frequently occur on thenbsp;stems and leaves of ferns and other plants in tropical forests.nbsp;Such small and comparatively delicate plants would, however,nbsp;be easily rubbed off or destroyed in the process of fossilisation,nbsp;and it is extremely rare to find among petrified Palaeozoicnbsp;plants the external features well preserved. It is probablenbsp;that the forests extended over low lying and swampy regions,nbsp;and that, in part, the trees were rooted in a submerged surface.nbsp;Under such conditions of growth there would not be the samenbsp;abundance of Bryophytes as in most of our modern forests.

To whatever cause the absence of mosses may be best attributed, it is a fact that should not be too strongly emphasised in discussions on plant-evolution.

leaves, with a delicate lamina, without veins or with a single median vein, arranged in a spiral manner on the stem.

Aluscites^ is one of those convenient generic designations which limited knowledge and incomplete data render necessary�nbsp;in palaeontology. Fossil plants which in their general habitnbsp;bear a sufficiently striking resemblance to recent mosses, maynbsp;be included under this generic name.

1. Muscites polytrichaceus Renault and Zeiller. In this species the stems are about 3�4 cm. long and 1'3 m. broad,nbsp;usually simple, but sometimes giving off a few branches, andnbsp;marked externally by very delicate longitudinal grooves. Thenbsp;leaves are alternate, closely arranged, lanceolate, with an acutenbsp;apex, gradually narrowed towards the base, 1�2 mm. long,nbsp;traversed by a single median vein.

One of the French specimens, on which the species was founded^, is shown in fig. 51, and the form of the leaves isnbsp;more clearly seen in the small enlarged piece of stem. Thenbsp;authors of the species point out that the tufted habit of thenbsp;specimens, their small size, and the membranous characternbsp;of the leaves, all point to the Musci as the Class to whichnbsp;the plant should be referred in spite of the absence of reproductive organs.

Among recent mosses, the genus Rhizogoniuni,�one of the Mniaceae,�and Polytrichum are spoken of as offering a close

resemblance to the fossil form. The type-specimen was found in the Coal-Measures of Commentry, and is now in the Museum ofnbsp;the �cole des Mines in Paris; the figure given by MM. Renaultnbsp;and Zeiller faithfully represents the appearance of the plant.

It has been suggested�- that some small twigs figured by Lesquereux� from the Coal-Measures of North America asnbsp;Lycopodites Meeki Lesq., may possibly be mosses. The specimens do not appear to be at all convincing, and cannot wellnbsp;be included as probable representatives of Palaeozoic Musci.nbsp;Lycopodites Meeki Lesq. bears a close resemblance to thenbsp;recent Selaginella Oregana shown in fig. 48, C.

From Mesozoic rocks we have no absolutely trustworthy fossil mosses. The late Prof Heer� has quoted the occurrencenbsp;of certain fossil Caterpillars in Liassic beds as indicative ofnbsp;the existence of mosses, but evidence of this kind cannot benbsp;accepted as scientifically sound. In 1850 Buckman^ describednbsp;and figured a few fragments of plants from a freshwater limestone at the base of the Lias series near Bristol. Amongnbsp;others he described certain specimens as examples of a fossilnbsp;Monocotyledon, under the generic name Najadita. Mr Starkienbsp;Gardner� subsequently examined the specimens, and suggestednbsp;that the Lias fragments referred to Najadita should be compared with the recent freshwater moss Fontinalis. In thisnbsp;opinion he was supported by Mr Carruthers and Mr Murray ofnbsp;the British Museum. In a footnote to the memoir in whichnbsp;this suggestion is made, Gardner refers to a moss-capsule fromnbsp;the same beds, which he had received from Mr Brodie. Throughnbsp;the kindness of the latter gentleman, I have had an opportunitynbsp;of examining the supposed capsule, and have no hesitation innbsp;describing it as absolutely indeterminable. It is in the form ofnbsp;an irregularly oval brown stain on the surface of the rock, withnbsp;the suggestion of a stalk at one end, but there are no groundsnbsp;for describing the specimen as a moss-capsule, or indeed anythingnbsp;else. The type-specimens figured by Brodie and subsequentlynbsp;referred to a moss are now in the British Museum; they are

� Solms-Laubach (91) p. 186. nbsp;nbsp;nbsp;^ Lesquereux (79) PI. lxii. fig. 1.

� Heer (65) p. 89. nbsp;nbsp;nbsp;^ Buckman (50) 1.nbsp;nbsp;nbsp;nbsp;� Gardner (86) p. 203.

small and imperfect fragments of slender stems bearing rather long oval leaves which might well have belonged to a moss.nbsp;The material is however too fragmentary to allow of accuratenbsp;diagnosis or determination.

2. Muscites ferrugineus (Ludg.). This species possesses a slender stem bearing crowded ovate-acuminate leaves. Thenbsp;capsules are cup-shaped, borne on a short stalk, with a circularnbsp;opening without marginal teeth. This fossil was first figurednbsp;and described by Ludwig^ from a brown ironstone of Miocenenbsp;age at Dernbach in Nassau. The author of the species placednbsp;it in the recent genus Gymnostomiim, and Schimper^ afterwardsnbsp;changed the generic name to Sphagnum, at the same timenbsp;altering the specific name to Ludivigi. The evidence is hardlynbsp;strong enough to justify a generic designation which impliesnbsp;identity with a particular recent genus, and it is a much safernbsp;plan to adopt the non-committal term Muscites, at the samenbsp;time retaining Ludwig�s original specific name. Without havingnbsp;examined the type-specimen it is impossible to express a definitenbsp;opinion as to the accuracy of the description given by Ludwig;nbsp;if the capsule is correctly identified it is the oldest examplenbsp;hitherto recorded of a fossil moss-sporogonium.

CHAPTEE IX.

The Pteridophytes include plants which vary in size from a few millimetres^ to several metres in height. The spore onnbsp;germination gives rise to a small thalloid structure, the pro-thallium, on which the sexual organs are developed; this is thenbsp;gametophyte or sexual generation. The sexual organs have thenbsp;form of typical archegonia and antheridia. From the fertilisednbsp;egg-cell there is developed the Pteridophyte plant or sporo-phyte, which bears the spores. This asexual generation showsnbsp;a well-marked external differentiation into stem and leaves, andnbsp;bears true roots. Internally the tissues exhibit a high degreenbsp;of differentiation into distinct tissue-systems. True vascularnbsp;bundles occur, which may or may not be capable of secondarynbsp;thickening by means of a cambium, i.e. a definitely localisednbsp;zone of meristematic tissue. The sporangia are borne either onnbsp;the ordinary foliage leaves or on special spore-bearing leavesnbsp;called sporophylls, which differ in a greater or less degree fromnbsp;the sterile leaves.

The majority of the best known and most important Palaeozoic genera are either true Vascular Cryptogams, ornbsp;possess certain of the pteridophytic characteristics combinednbsp;with those of higher plants. It is not merely the commonernbsp;and more familiar recent genera with which the student ofnbsp;extinct types must be acquainted, but it is extremely importantnbsp;^ e.g. the Fern Trichornanes Goehelianum Gies. Giesenhagen (92) p. 157-

that he should make himself familiar with the rarer, less known and more isolated recent forms, which often throw most light onnbsp;the affinities of the older representatives of the group. It isnbsp;often the case, the more isolated living plants are, the morenbsp;likely are they to afford valuable assistance in the interpretation of genera representing a class, which reached itsnbsp;maximum development in the earlier periods of the earth�snbsp;history. The importance of paying special attention to suchnbsp;recent plants as may be looked upon as survivals of a class nownbsp;tending towards extinction, will be more thoroughly realisednbsp;after the extinct vascular cryptogams have been dealt with.

A comparison of the Pteridophyta and Bryophyta brings out certain points of divergence. In the first place, the sporo-phyte assumes in the former class a much more prominentnbsp;role, and the gametophyte has suffered very considerable reduction. The gametophyte, i.e. the structure which is formednbsp;on the germination of the asexually-produced spore, is usuallynbsp;short-lived, small, and more or less dependent on the sporo-phyte for its nutrition. In a few cases only is it capable ofnbsp;providing itself with the essential elements of food. On'�thenbsp;other hand, the sporophyte, at a very earljr stage of its development becomes free from the gametophyte and is entirely self-supporting. Beproduction is effected as in the Bryophyta bynbsp;sexual reproductive organs and by asexual methods. Not onlynbsp;have we in the Pteridophytes a much more complete externalnbsp;division of the plant-body into definite members, which subservenbsp;distinct functions, and behave as well-defined physiologicalnbsp;organs adapted for taking a certain share in the life-functionsnbsp;of the individual, but the internal differentiation has reachednbsp;a much higher stage. True vascular tissue, consisting of xylemnbsp;and phloem, occurs for the first time in this class. The wholenbsp;plant is traversed by one or more vascular strands composednbsp;of xylem and phloem elements, which are respectively concerned with the distribution of inorganic and organic foodnbsp;substances.

The Pteridophyta include the most important fossil plants. It is from a study of the internal structure of various extinctnbsp;representatives of this class, that palaeobotanists have been

able to contribute facts of the greatest interest and importance towards the advancement of botanical science.

The botanist�s chief aim in the anatomical investigation of Palaeozoic genera is to discover data which point the way to anbsp;solution of the problems of plant-evolution. In the abundantnbsp;material afforded by the petrified remnants of ancient floras wenbsp;have the means of tracing the pa-st history of existing groups ornbsp;individual forms, and it is from the Palaeozoic Pteridophytesnbsp;that our most valuable results have been so far obtained.

In this and the following chapters of Volume I. two divisions of the Pteridophyta are dealt with in such detail asnbsp;the nature of the book allows. In the earlier chapters ofnbsp;Volume II. the remaining representatives of this class will benbsp;described. As in the preceding chapters such recent plantsnbsp;will be described as are most essential for the correct interpretation of the fossil forms.

It is impossible to do more than confine our attention to a few only of the genera of living plants which directly concernnbsp;us; some acquaintance with the general facts of plant morphology must be assumed. Among the most useful text-books ornbsp;books of reference on the Pteridophyta the student may consultnbsp;those mentioned in the footnote'.

Leaves usually small in proportion to the size of the whole plant, arranged in whorls at the nodes. Sporangia borne onnbsp;specially modified sporophylls or sporangiophores, which arenbsp;aggregated to form a definite strobilus or spore-bearing cone.

The leaves are in whorls, coherent in the form of a sheath, and traversed by longitudinal veins which do not fork or anasto-

1 Scott (96) a text-book for elementary students; a full account is given of liquisetum and other genera of primary importance. Vines (95) Part iii.nbsp;Campbell (95), Luerssen (89) in Eabenhorst�s Kryptogamen-Flora, vol. iii.. Vannbsp;�iegbem (91), de Bary (84), Baker (87).

mose. The stem is divided into comparatively long internodes separated by the leaf-bearing nodes, and the branches arise innbsp;the leaf-axils at the nodes. The fertile leaves or sporophyllsnbsp;differ from the sterile leaves, and usually occur in definitenbsp;aggregations or strobili containing spores of one kind {iso-sporous). In the single living genus Equisetum, the outernbsp;coat of the mature spore forms two hygroscopically sensitivenbsp;filamentous structures or elaters. On the germination of thenbsp;spore the gametophyte is developed in the form of a small lobednbsp;prothallium 1�2 cm. in length. In most cases there are distinctnbsp;male and female prothallia.

The genus Equisetum L., the common Horse-tail, is the sole living representative of this Family. It occurs as a commonnbsp;native plant in Britain, and has a wide geographical distribution.nbsp;Species of Equisetum are abundant in the temperate zonesnbsp;of both hemispheres, and occur in arctic as well as tropicalnbsp;latitudes. Wallace^ speaks of Horse-tails, � very like our ownnbsp;species,� growing at a height of 5000 feet on the Pangerangonbsp;mountain in Java. In favourable situations the large Brjtishnbsp;Horse-tail, Equisetum maximum Lam. (= E. Telmateia Erhb.),nbsp;occasionally reaches a height of about six feet, and growing innbsp;thick clusters forms miniature forests of trees with slendernbsp;erect stems and regular circles of long and thin branches.nbsp;A tropical species, Equisetum gigaiitemn Linn.''* living in thenbsp;marshes of Mexico and Cuba^, and extending southward tonbsp;Buenos Ayres and Chili, reaches a height of twenty to fortynbsp;feet, but the stem always remains slender, and does not exceednbsp;an inch in diameter. Groves of such tall slender plants onnbsp;the eastern slopes of the Andes** suggest to the palaeobotanistnbsp;an enfeebled forest-growth recalling the arborescent Calamitesnbsp;of a Palaeozoic vegetation. The twenty-five existing speciesnbsp;of Equisetum are remnants of various generic types of formernbsp;epochs, and possess a special interest from the point of viewnbsp;of the geological history of plants. A brief description of the

^ Baker (87) p. 4. Hooker, W. J. (61) PI. lxxiv. Vide also Milde (67) for figures of Equisetum.

main characters of the recent genus will enable the student to appreciate the points of difference and agreement between thenbsp;extinct and present representatives of the Equisetales.

Fig. 52. Equisetum maximum Lam. A. Fertile shoot with strobilus and sterile leaf-sheaths [after Luerssen (89); slightly less than nat. size].

B. nbsp;nbsp;nbsp;Sporophyll bearing open sporangia (after Luerssen; slightly enlarged).

C. nbsp;nbsp;nbsp;Part of a transverse section (diagrammatic); v, vallecular canals, e, en-dodermis, c, carinal canals (after Luerssen; x 20). D. Equisetum arvensenbsp;L. Part of a transverse section of an internode of a sterile shoot.

D. nbsp;nbsp;nbsp;cortex, e, endodermis, x, xylem traoheids, a remains of annular traoheidsnbsp;of the protoxylem, c, carinal canal (after Strasburger; x 90).

Equisetum.

The plant consists of a perennial underground creeping rhizome, branching into secondary rhizomes, divided into well-marked nodes and internodes. From the nodes are given off

two sets of buds, which may develope into ascending aerial shoots or descending roots. At each node is a leaf-sheath morenbsp;or less deeply divided along the upper margin into teethnbsp;representing the tips of coherent leaves (fig. 52, A).

In some species one or more internodes of underground branches become considerably swollen and assume the form ofnbsp;ovate or elliptical starch-storing tubers, which are capable ofnbsp;giving rise to new plants by vegetative reproduction. Tubers,nbsp;either singly or in chains, occur in E. arvense Linn., E. silvaticumnbsp;Linn., E. maximum Lam., among British species.

Fig. 53. Ehizome (E) of Equisetum palustre h. with a thin shoot giving off roots and tuberous branches from a node [after Duval-Jouve (64)].

In the example shown in fig. 53 (Equisetum palustre L.^) the stout rhizome R gives off from its node, marked by a smallnbsp;and irregular leaf-sheath, two thin roots and a single shoot.nbsp;The latter has a leaf-sheath at its base, and from the secondnbsp;node, with a larger leaf-sheath, there have been developednbsp;branches with tuberous internodes; the constrictions between

the tubers and the tips of the terminal tubers bear small leaf-sheaths. Branched roots are also given off from the upper node of the erect shoot.

Near the surface of the ground the buds on the rhizome nodes develope into green erect shoots. The shoot axis isnbsp;marked out into long internodes separated by nodes bearingnbsp;the leaf-sheaths. The surface of each internode is traversednbsp;by regular and more or less prominent longitudinal ridges andnbsp;grooves; each ridge marking the position of an internal longitudinal vascular strand. In the axil of each leaf, that is in thenbsp;axil of each portion of a leaf-sheath corresponding to a marginalnbsp;uni-nerved tooth, there is produced a lateral bud which maynbsp;either remain dormant or break through the leaf-sheath andnbsp;emerge as a lateral branch. At the base of each branch annbsp;adventitious root may be formed from a cell immediately belownbsp;the first leaf-sheath, but in aerial shoots the roots usuallynbsp;remain undeveloped. The lateral branches repeat on a smallernbsp;scale the general features of the main axis. In some species,nbsp;the shoots are unbranched, and in others the slender branchesnbsp;arise in crowded whorls from each node. Leaves, roots andnbsp;branches are given off in whorls, and the whorls from each nodenbsp;alternate with those from the node next above and next below.

In some species of Equisetmn the aerial stem terminates in a conical group of sporophylls, while in others the strobilus isnbsp;formed at the apex of a pale-coloured fertile shoot, which nevernbsp;attains any considerable length and dies down early in thenbsp;season of growth (fig. 52, A). Below the terminal cone ornbsp;strobilus there occur one or two modified leaf-sheaths. Suchnbsp;a ring of incompletely developed leaves intervening betweennbsp;the cone of sporangiophores and the normal leaves, is known asnbsp;the annulus. The annulus is seen in fig. 52, A, immediatelynbsp;below the lowest whorl of sporophylls; it has the form of a lownbsp;sheath with a ragged margin. In the region of the cone thenbsp;internodes remain shorter, and the whorls of appendages, knownnbsp;as sporophylls or sporangiophores, have the form of stalkednbsp;structures terminating distally in a hexagonal peltate disc,nbsp;which bears on its inner face a ring of five to ten oval sporangianbsp;(fig. 52, B). Each sporangium contains numerous spores which

eventually escape by the longitudinal dehiscence of the spor-angial wall. The opening of the sporangia is probably assisted by the movements of the characteristic elaters formed from thenbsp;outer wall of each spore.

The spores, which are capable of living only a short time, grow into aerial green prothallia, 1�2 cm. in length; these havenbsp;the form of irregularly and more or less deeply lobed structures.nbsp;On the larger and more deeply lobed prothallia the archegonianbsp;or female reproductive organs are borne, and the smaller ornbsp;male prothallia bear the antheridia. On the fertilisation of annbsp;egg-cell, the Eqiiisetiim plant is gradually developed. For anbsp;short time parasitic on the female prothallium or gametophyte,nbsp;the young plant soon takes root in the ground and becomesnbsp;completely independent.

As seen in transverse section through a young stem near the apex, the axis consists of a mass of parenchyma, in which maynbsp;be distinguished a central larger-celled tissue, surrounded by anbsp;ring of smaller-celled groups marking the position of a circle ofnbsp;embryonic vascular strands. In each young vascular strand, anbsp;few of the cells next the pith may be seen to have thicker wallsnbsp;and to be provided with a ring-like internal thickening; thesenbsp;have passed over into the condition of annular tracheids andnbsp;represent the protoxylem elements. At a later stage, anbsp;transverse section through the stem shows a central hollownbsp;pith, formed by the tearing apart and subsequent disappearancenbsp;of the medullary parenchymatous cells, which were unable tonbsp;keep pace with the growth in thickness of the stem. The pithnbsp;cavity is bridged across at each node by a multi-layered plate ofnbsp;parenchyma, which forms the so-called nodal diaphragm. Thenbsp;inner edge of each vascular strand is now found to be occupiednbsp;by a small irregularly circular canal (fig. 52, C, c, and D, c) innbsp;which may be seen some of the rings of protoxylem tracheidsnbsp;(D, a) which have been torn apart and almost completelynbsp;destroyed. These canals, known as carinal canals, have arisennbsp;by the tearing and disruption of the thin-walled cells in thenbsp;immediate neighbourhood of the protoxylem. Each carinalnbsp;canal is bounded by a layer of elongated parenchymatous cellsnbsp;which form part of the xylem of the vascular bundle, and is

succeeded internally by the general ground-tissue of the stem. The xylem parenchyma next a carinal canal is succeedednbsp;externally by phloem tissue, consisting of short protoplasmicnbsp;cells and longer elements, without nuclei and poor in contents ;nbsp;the latter may be regarded as sieve-tubes. On either side ofnbsp;the phloem, the x}dem occurs in two separate bands or groupsnbsp;of annular and reticulately thickened tracheids. In some species,nbsp;e.g. Equisetum xylochaetum Metten.^ and E. giganteum'^ L.nbsp;a native of South America, the xylem has the form of twonbsp;bands composed of fairly numerous tracheids, but in mostnbsp;species three xylem tracheids occur in small groups, as shownnbsp;in the figure of E. maximum (fig. 52, D). In the shape of thenbsp;vascular bundle, and in the formation of the carinal canal, therenbsp;is a distinct resemblance between the vascular bundles ofnbsp;Equisetum and those of a monocotyledonous stem. Thesenbsp;collateral stem-bundles of xylem and phloem traverse eachnbsp;internode as distinct strands, and at the nodes each strand forksnbsp;into two branches (fig. 54, A), which anastomose with thenbsp;alternating bundles passing into the stem from the leaf-sheath.

Thus the vascular strands of each internode alternate in position with those of the next internode.

There are certain points connected with the vascular bundles in the nodal region of a shoot, which have an important bearingnbsp;on the structure of fossil equisetaceous stems. Fig. 54 Bnbsp;represents a diagrammatic longitudinal section through thenbsp;node of a rhizome of Equisetum arvense from which a root h isnbsp;passing off in a downward direction, and a branch in an upwardnbsp;direction. The black band c in the parent stem shows thenbsp;position of the vascular strands; in the region of the node thenbsp;vascular tissue attains a considerable thickness, as seen at d innbsp;the figure. The bands passing out to the left from d go tonbsp;supply the branch and root respectively. The increased breadthnbsp;of the xylem strands at the node is due to the intercalation of anbsp;number of short tracheids. Fig. 55, 4 shows a transverse sectionnbsp;through a mature node of Equisetum maximum; px marksnbsp;the position of the protoxylem and e that of the endodermis.nbsp;On comparing this section with that of the internodal vascularnbsp;bundle in fig. 52, D, the much greater development of wooeBinnbsp;the former is obvious; the carinal canal of the internodal bundlenbsp;is absent in the section through a node. The disposition of thenbsp;xylem tracheids in fig. 55, 4 shows a certain regularity which,nbsp;though not very well marked, suggests the development of woodnbsp;elements as the result of cambial activity. Longitudinal sectionsnbsp;through the nodal region demonstrate the existence of �cellsnbsp;similar to those of an ordinary cambium, and a cell-formationnbsp;resulting from their division which is similar to that in annbsp;ordinary secondary thickening.�� The short tracheids whichnbsp;make up this nodal mass of xylem differ from those in thenbsp;internodal bundle in their smaller size, and in being reticulatelynbsp;thickened. There is, therefore, evidence that in the nodes ofnbsp;some Equisetum stems additional xylem elements are produced bynbsp;a method of growth comparable with the cambial activity whichnbsp;brings about the growth in thickness of a forest-tree^. The

^ Williamson and Scott (94) p. 877. These authors, in referring to Cormack�s description of the secondary nodal wood of E. maximum, express doubts as tonbsp;the existence of such secondary growth in all species of the genus.

significance of- these statements will be realised when the structure of the extinct genus Calamites is described andnbsp;compared with that of Equisetum.

The small drawing in fig. 55, 3 shows part of the ring of thick nodal wood; the section cuts through two bundles aboutnbsp;their point of bifurcation, the strand x is passing out in anbsp;radial direction to a lateral branch, the strand to the right ofnbsp;X and the separate fragment of a strand to the left of x arenbsp;portions of leaf-trace buirdles on their way to the leaf-sheath.nbsp;Reverting to fig. 54, B, the other structures seen in the sectionnbsp;are the leaf-sheaths (Z and m), the vallecular canal (�), thenbsp;epidermis, cortex and pith (k, e and a) of the stem. Thenbsp;epidermis which has been ruptured by the root and branch isnbsp;indicated at i, i; the dotted lines traversing the upper part ofnbsp;the pith of the lateral branch mark the position of a nodalnbsp;diaphragm.

Fig. 55. 1. Transverse section of a root of Equisetum variegatum Sohl., e endo-dermis, or outer layer of the phloeoterma (after Pfitzer; x 160). 2. Transverse section of rhizome of E. maximum, slightly enlarged. 3. Transverse section through a node of E. maximum, x, branch of vascular strand (slightlynbsp;enlarged). 4. Transverse section through a node of E. maximum showingnbsp;the mass of xylem, px protoxylem ( x 175). (Figs. 3 and 4 after Cormaok.)

Immediately external to each vascular strand, as seen in transverse section, there is a layer of cells containing starch.

and this is followed by a distinct endodermis, of which the cells show the characteristic black dot in the cutictdarised radialnbsp;walls (fig. 52, D). Beyond the endodermis there is the large-celled parenchyma of the rest of the cortex. Tannin cells occurnbsp;here and there scattered among the ground tissue. On thenbsp;same radius on which each vascular strand occurs, the corticalnbsp;parenchyma passes into a mass of sub-epidermal thick-wallednbsp;mechanical tissue or stereome. Alternating with the ridges ofnbsp;stereome, the grooves are occupied by thin-walled chlorophyll-containing tissue which carries on most of the assimilatingnbsp;functions, and communicates with the external atmosphere bynbsp;means of stomata arranged in vertical rows down each internode.nbsp;The continuity of the cortical tissue is interrupted by thenbsp;occurrence of large longitudinal vallecular canals alternating innbsp;position with the stem ridges and vascular strands (fig. 52, C, v).nbsp;The epidermis consists of a single layer of cells, containingnbsp;.stomata, and with the outer cell-walls impregnated with silica.

In certain species of Equisetuni, e.g. E. palustre L., the whole circle of vascular strands is enclosed by an endodermis, and hasnbsp;the structure typical of a monostelic stem. In others e.g. E.nbsp;litorale K�hl. each vascular strand is surrounded by a separatenbsp;endodermis, and in some forms e.g. E. silvaticum L. there is annbsp;inner as well as an outer endodermal laimrt Without discussingnbsp;the explanation given to this variation in the occurrence of thenbsp;endodermis, it may be stated that in all species of Equisehminbsp;the stem may be regarded as monostelic^.

In the rhizome the structure agrees in the main with that of the green shoots, but the vallecular canals attain a largernbsp;size, and the pith is solid. A slightly enlarged transverse section of a rhizome of Equisetuni maximum is shown in fig. 55, 2,nbsp;the small circles surrounding the pith mark the position ofnbsp;the vascular bundles and carinal canals; the much larger spacesnbsp;between the central cylinder and the surface of the stem are thenbsp;vallecular canals.

The central cylinder or stele of the root is of the diarch, triarch or tetrach type; i.e. there may be 2, 3 or 4 groups of

protoxylein in the xylem of the root stele. The axial portion is occupied by large tracheids, and the smaller tracheids of thenbsp;xylem occur as radially disposed groups, alternating with groupsnbsp;of phloem. External to the xylem and phloem strands therenbsp;occur two layers of cells, usually spoken of as a double endo-dermis, but it has been suggested that it is preferable tonbsp;describe the double layer as the phloeoterma^, of which thenbsp;inner layer has the functions of a pericycle, and the outer thatnbsp;of an endodermis. A transverse section of a root is seen innbsp;fig. 55, 1, the dark cells on the left are part of a thick band ofnbsp;sclerenchyma in the cortex of the root, the layer e is the outernbsp;layer of the phloeoterma.

Without describing in detail the development'^ of the sporangia, it should be noted that the sporangial wall is at firstnbsp;3 to 4 cells thick, but it eventually consists of a single layer. Thenbsp;cells have spiral thickening bands on the ventral surface, andnbsp;rings on the cells where the longitudinal splitting takes place.nbsp;Each sporangium is supplied by a vascular bundle which isnbsp;given off from that of the sporangiophore axis. The strobilinbsp;are isosporous.

In dealing with the fossil Equisetales, we will first consider the genera Equisetites, Phyllotheca and Schizoneura, and afterwards describe the older and better known genera Catamitesnbsp;and Archaeocalamites. A thoroughly satisfactory classificationnbsp;of the members of the Equisetales is practically impossiblenbsp;without more data than we at present possess. It has been thenbsp;custom to include Equisetites, Phyllotheca and Schizoneura innbsp;the family Equisetaceae, and to refer Catamites and Archaeo-

calamites to the Calamarieae; such a division rests in part on assumption, and cannot be considered final. When we attemptnbsp;to define the Equisetales and the two families Equisetaceae andnbsp;Calamarieae, we find ourselves seriously hampered by lack ofnbsp;knowledge of certain important characters, which should benbsp;taken into account in framing diagnoses. There is little harmnbsp;in retaining provisionally the two families already referred to, ifnbsp;we do not allow a purely arbitrary classification to prejudice ournbsp;opinions as to the affinities of the several members of the Equi-setales.

The Equisetaceae might be defined as a family including plants which were usually herbaceous but in some cases arborescent, bearing verticils of leaves in the form of sheaths more ornbsp;less deeply divided into segments or teeth. The strobili werenbsp;isosporous and consisted of a central axis bearing verticils ofnbsp;distally expanded sporophylls with sporangia, as in Equisetum.nbsp;The genus Equisetites might be included in this family, but itnbsp;must be admitted that we know next to nothing as to itsnbsp;anatom}^ and we cannot be sure that the strobili were alwaysnbsp;isosporous.

The genus Schizoneura is too imperfectly known to be defined with any approach to completeness, or to be assigned tonbsp;a family defined within certain prescribed limits. FKyllothecanbsp;is another genu^ about which we possess but little satisfactorynbsp;knowledge'; we are still without evidence as to its structure,nbsp;and the descriptions of the few strobili that are known are notnbsp;consistent. Recent work points to a probability of Phyllothecanbsp;being closely allied to Annularia, a genus included in thenbsp;Calamarieae, and standing for a certain type of Calamiteannbsp;foliage-shoots.

In comparing the Calamarieae with the Equisetaceae, the alternation of sterile and fertile whorls in the strobilus, and thenbsp;free linear leaves at the nodes instead of leaf-sheaths are twonbsp;characters made use of as distinguishing features of the genusnbsp;Calamites as the type of the Calamarieae. On the other hand,nbsp;the strobili of Phyllotheca appear to agree with those of Gala-mites rather than with those of Equisetum, and strobili ofnbsp;Archaeocalamites have been found exhibiting the typical

Equisetum characters. The sheath-like form of the leaves is not necessarily peculiar to the Equisetaceae, and we have evidencenbsp;that leaf-sheaths occurred on the nodes of Calamitean plants.nbsp;In Archaeocalamites the leaves possess characteristic features,nbsp;and can hardly be said to agree more closely with those ofnbsp;Calamites than with the leaves of Phyllotheca or Sphenophyllum,nbsp;a genus belonging to another class of Pteridophytes.

On the whole, then, without discussing further the possibilities of a subdivision of the Equisetales, we may regard the genera Calamites, Archaeocalamites, Equisetites, Equisetum,nbsp;Phyllotheca and Schizoneura as so many members of the Equisetales, without insisting on a classification which cannot benbsp;supported by satisfactory evidence.

Our knowledge of Calamites is fairly complete. Abundant and well-preserved material from the Coal-Measures of England,nbsp;and from Permo-Carboniferous rocks of France, Germany andnbsp;elsewhere, has enabled palaeobotanists to investigate the anatomical characters of both the vegetative and reproductivenbsp;structures of this genxis. We are in a position to give anbsp;detailed diagnosis of Calamitean stems, roots and strobili, andnbsp;to determine the place of this type of plant in a system ofnbsp;classification. Calamites not only illustrates the possibilities ofnbsp;palaeobotanical research, but it demonstrates the importance ofnbsp;fossil forms as foundations on which to construct the mostnbsp;rational classification of existing plants. The close alliancenbsp;between Calamites and the recent Equisetaceae has beennbsp;clearly established, and certain characteristics of the formernbsp;genus render necessary an extension and modification of thenbsp;definition of the class to which both Calamites and Equisetitesnbsp;belong. The Calamites broaden our conception of the Equi-setaceous alliance, and by their resemblance to other extinctnbsp;Palaeozoic types they furnish us with important links towardsnbsp;a phylogenetic series, which the other members of the Equisetales do not supply.

From the Upper Devonian to the Permian epoch Calamites and other closely related types played a prominent part in thenbsp;vegetation of the world. We have no good evidence for thenbsp;existence of Calamites in Triassic times; in its place there were

gigantic Equisetums which resembled modern Horse-tails in a remarkable degree. In the succeeding Jurassic period tree-likenbsp;Equisetums were still in existence, and species of Equisetitesnbsp;are met with in rocks of this age in nearly all parts of thenbsp;world. A few widely distributed species are known fromnbsp;Wealden rocks, but as we ascend the geologic series from thenbsp;Jurassic strata, the Equisetums become less numerous andnbsp;the individual plants gradually assume proportions practicallynbsp;identical with those of existing forms.

The generic name Equisetites was proposed by Sternberg in 1838¹ as a convenient designation for fossil stems bearing anbsp;close resemblance to recent species oi Equisetum. Some authorsnbsp;have preferred to apply the name Equisetum to fossil and recentnbsp;species alike, but in spite of the apparent identity in thenbsp;external characters of the fossil stems with those of existingnbsp;Horse-tails, and a close similarity as regards the cones, therenbsp;are certain reasons for retaining Sternberg�s generic name. Itnbsp;is important to avoid such nomenclature as might appear tonbsp;express more than the facts admit. If the custom of adding thenbsp;termination -ites to the root of a recent generic term is generallynbsp;followed, it at once serves to show that the plants so namednbsp;are fossil and not recent species. Moreover, in the case ofnbsp;fossil Equisetums we know nothing of their internal structure,nbsp;and our comparisons are limited to external characters. Stems,nbsp;cones, tubers, and leaves are often very well preserved as sandstone casts with distinct surface-markings, but we are still innbsp;want of petrified specimens. There is indeed evidence thatnbsp;some of the I'riassic and Jurassic species of Equisetites, like thenbsp;older Calamites, possessed the power of secondary growth innbsp;thickness, but our deductions are based solely on externalnbsp;characters.

In the following pages a few of the better known species of Equisetites are briefly described, the examples being chosen

partly with a view to illustrate the geological history of the genus, and partly to contribute something towards a fullernbsp;knowledge of particular species. One of the most striking factsnbsp;to be gleaned from a general survey of the past history ofnbsp;the Equisetaceae is the persistence since the latter part of thenbsp;Palaeozoic period of that type of plant which is represented bynbsp;existing Equisetums. There is perhaps no genus in existencenbsp;which illustrates more vividly than Eqidsetum the survival ofnbsp;an extremely ancient group, which is represented to-day bynbsp;numerous and widely spread species. The Equisetaceousnbsp;characteristics mark an isolated division of existing Vascularnbsp;Cryptogams, and without reference to extinct types it isnbsp;practically impossible to do mote than vaguely guess at thenbsp;genealogical connections of the family. When we go back tonbsp;Palaeozoic plants there are indications of guiding lines whichnbsp;point the way to connecting branches between the older Equi-setales and other classes of Pteridophytes. The recentlynbsp;discovered genus Cheirostrohus^ is especially important fromnbsp;this point of view.

The accurate description of species, and the determination of the value of such differences as are exhibited in the surfacenbsp;characters of structureless casts, are practically impossible innbsp;many of the fossil forms. In certain living Horse-tails we findnbsp;striking difi'erences between fertile and sterile shoots, andnbsp;between branches of different orders. The isolated occurrencenbsp;of fragments of fossil stems often leads to an artificial separation of �species� largely founded on differences in diameter,nbsp;or on slight variations in the form of the leaf-sheaths. It isnbsp;wiser to admit that in many cases we are without the means ofnbsp;accurate diagnosis, and that the specific names applied to fossilnbsp;Equisetums do not always possess much value as criteria ofnbsp;taxonomic differences.

The specimens of fossil Equisetums are usually readily recognised by the coherent leaf-segments in the form of nodal sheaths resembling those of recent species. The tissues of the cortexnbsp;and central cylinder are occasionally represented by a thin layer

of coal pressed on to the surface of a sandstone cast, or covering a flattened stem-impression on a piece of shale. It is sometimesnbsp;possible under the microscope to recognise on the carbonisednbsp;epidermal tissues the remains of a surface-ornamentationnbsp;similar to that in recent species, which is due to the occurrencenbsp;of siliceous patches on the superficial cells. Longitudinal rowsnbsp;of stomata may also be detected under favourable conditions ofnbsp;preservation. The nodal diaphragms of stems have occasionallynbsp;been preserved apart, but such circular and radially-striatednbsp;bodies may be misleading if found as isolated objects. Castsnbsp;of the wide hollow pith of Equisetites, with longitudinal ridgesnbsp;and grooves, and fairly deep nodal constrictions, have oftennbsp;been mistaken for the medullary casts of Calamites.

Several species of Equisetites have been recorded from the Upper Coal-Measures and overlying Permian rocks, but thesenbsp;present special difficulties. In one instance described below,nbsp;{Equisetites Hemingwayi Kidst.), the species was founded on anbsp;cast of what appeared to be a strobilus made up of sporophyllsnbsp;similar to those in an Equisetum cone. In other Permp-Garboniferous species the choice of the generic name Equisetitesnbsp;has been determined by the occurrence of leaf-sheaths eithernbsp;isolated or attached to the node of a stem. The question tonbsp;consider is, how far may the Equisetum-like leaf-sheath benbsp;regarded as a characteristic feature of Equisetites as distinctnbsp;from Calamites ? In the genus Calamites the leaves arenbsp;generally described as simple linear leaves arranged in a whorlnbsp;at the nodes, but not coherent in the form of a sheath (fig. 85).nbsp;The fusion of the segments into a continuous sheath or collarnbsp;is regarded as a distinguishing characteristic of Equisetites andnbsp;Equisetum. The typical leaf-sheath of a recent Horse-tail hasnbsp;already been described. In some species we have fairly largenbsp;and persistent free teeth on the upper margin of the leaf-sheath,nbsp;but in other Equisetums the rim of the sheath is practicallynbsp;straight and has a truncated appearance, the distal ends of thenbsp;segments being separated from one another by very slightnbsp;depressions, as in a portion of the sheath of Equisetum ramo-sissimurn Desf of fig. 58, C. In other leaf-sheaths of thisnbsp;species there are delicate and pointed teeth adherent to the

margin of the coherent segments; the teeth are deciduous, and after they ha.ve fallen the sheath presents a truncated appearance. This difference between the sheaths to which the teethnbsp;are still attached and those from which they have fallen isnbsp;illustrated by fig. 58, B and C; it is one which should be bornenbsp;in mind in the description of fossil species, and has probablynbsp;been responsible for erroneous specific diagnoses. In somenbsp;recent Horse-tails the sheath is occasionally divided in one ornbsp;two places by a slit reaching to the base of the coherentnbsp;segments^; this shows a tendency of the segments towards thenbsp;free manner of occurrence which is usually considered a Cala-mitean character. In certain fossils referred to the genusnbsp;Annularia, the nodes bear whorls of long and narrow leavesnbsp;which are fused basally into a collar (fig. 58, B). There arenbsp;good grounds for believing that at least some Annularias werenbsp;the foliage shoots of true Calamites. Again, in some species ofnbsp;Galamitina, a sub-genus of Calamites, the leaves appear to havenbsp;been united basally into a narrow sheath. We see, then, thatnbsp;it is a mistake to attach great importance to the separate ornbsp;coherent character of leaf-segments in attempting to draw anbsp;line between the true Calamites and Equisetites. Potonie-

Fio. 56. Calamitean leaf-sheath. From a specimen in the Woodwardian Museum, a, base of leaf-sheath ; (very slightly reduced).

while pointing out that this distinction does not possess much value as a generic character, retains the genus Equisetites fornbsp;certain Palaeozoic Equisetum-like leaf-sheaths.

Fig. 56 represents a rather faint impression of a leaf-sheath and nodal diaphragm. The specimen is from the Coal-Measuresnbsp;of Ardwick, Manchester. The letter a probably points to thenbsp;attachment of the sheath to the node of the stem. The flattenednbsp;sheath is indistinctly divided into segments, and at the middlenbsp;of the free margin there appears to be a single free tooth. Thenbsp;lower part of the specimen, as seen in the figure, shows thenbsp;position of the nodal diaphragm. Between the diaphragm andnbsp;the sheath there are several slight ridges converging towardsnbsp;the nodal line ; these agree with the characteristic ridges andnbsp;grooves of Calamite casts which are described in detail innbsp;Chapter X. There is another specimen in the Britishnbsp;Museum which illustrates, rather more clearly than that shownnbsp;in fig. 56, the association of a fused leaf-sheath with a type ofnbsp;cast usually regarded as belonging to a Calamitean stem.nbsp;Some leaf-sheaths of Permian age described by Zeiller^ asnbsp;Equisetites Vaujolyi bear a close resemblance to the sheath innbsp;fig. 58 E. The nature of the true Calamite leaves is considerednbsp;more fully on a later page.

The examples of supposed Equisetites sheaths referred to below may serve to illustrate the kind of evidence on whichnbsp;this genus has been recorded from Upper Palaeozoic rocks. Inbsp;have retained the name Equisetites in the description of thenbsp;species, but it would probably be better to speak of suchnbsp;specimens as � Calamitean leaf-sheaths � rather than to describenbsp;them as definite species of Equisetites. We have not as yet anynbsp;thoroughly satisfactory evidence that the Equisetites of Triassicnbsp;and post-Triassic times existed in the vegetation of earliernbsp;periods.

In Grand�Eury�s Flore du Gard^ a fossil strobilus is figured under the name Calamostachys temdssima Grand�Eury, whichnbsp;consists of a slender axis bearing series of sporophylls and

1 Zeiller (92-) p. 56, PI. xii. Other similar leaf-sheaths have been figured by Germar (44) PI. x., Schimper (74) PI. xvii. and others.

sporangia apparently resembling those of an Equisetum. There are no sterile appendages or bracts alternating with the sporo-phylls ; and the absence of the former suggests a comparisonnbsp;with Equisetites rather than Galamites. Grand�Eury refers tonbsp;the fossil as � parfois a peine perceptible,� and a recent examination of the specimen leads me to thoroughly endorse thisnbsp;description. It was impossible to recognise the features represented in Grand�Eury�s drawing. Setting aside this fossil, therenbsp;are other strobili recorded by Renault' and referred by him to the

genus Bornia (Archaeocalamites), which also exhibit the Equi-setum-like character; the axis bears sporophylls only and no sterile bracts. It would appear then that in the Palaeozoicnbsp;period the Equisetaceous strobilus, as we know it in Equisetum,nbsp;was represented in some of the members of the Equisetales.

Mr Kidston* founded this species on a few specimens of cones found in the Middle Coal-Measures of Barnsley innbsp;Yorkshire. The best example of the cone described by Kidstonnbsp;has a length of 2�5 cm., and a breadth of 1'5 cm.; the surfacenbsp;is divided up into several hexagonal areas 4 mm. high andnbsp;5 mm. wide. Each of these plates shows a fairly prominentnbsp;projecting point in its centre; this is regarded as the point ofnbsp;attachment of the sporangiophore axis which expanded distallynbsp;into a hexagonal plate bearing sporangia. An examination ofnbsp;Mr Kidston�s specimens enabled me to recognise the closenbsp;resemblance which he insists on between the fossils and suchnbsp;a recent Equisetaceous strobilus as that of Equisetum limoiumnbsp;Sm. Nothing is known of the structure of the fossils beyondnbsp;the character of the superficial pattern of the impressions, andnbsp;it is impossible to speak with absolute confidence as to theirnbsp;nature. The author of the species makes use of the genericnbsp;name Equisetum', but in view of our ignorance of structuralnbsp;features it is better to adopt the more usual term Equisetites.

Since Kidston�s description was published I noticed a specimen in the British Museum collection which throws somenbsp;further light on this doubtful fossil. Part of this specimen isnbsp;shown in fig. 57, A. The stem is 21 cm. in length and aboutnbsp;5 mm. broad; it is divided into distinct nodes and internodes;nbsp;the former being a little exaggerated in the drawing. Thenbsp;surface is marked by fine and irregular striations, and in onenbsp;or two places there occur broken pieces of narrow linear leavesnbsp;in the neighbourhood of a node. Portions of four cones occurring in contact with the stem, appear to be sessile on the nodes.

but the preservation is not sufificiently good to enable one to speak with certainty as to the manner of attachment. Eachnbsp;cone consists of regular hexagonal depressions, which agreenbsp;exactly with the surface characters of Kidston�s type-specimen.nbsp;The manner of occurrence of the cones points to a lateral andnbsp;not a terminal attachment. The stem does not show any tracesnbsp;of Equisetaceous leaf-sheaths at the nodes, and such fragmentsnbsp;of leaves as occur appear to have the form of separate linearnbsp;segments; they are not such as are met with on Equisetites.nbsp;It agrees with some of the slender foliage-shoots of Calamiteannbsp;plants often described under the generic name Asterophyllites.nbsp;As regards the cones; they differ from the known Calamiteannbsp;strobili in the absence of sterile bracts, and appear to consistnbsp;entirely of distally expanded sporophylls as in Equisetum. Thenbsp;general impression afforded by the fossil is that we have notnbsp;sufficient evidence for definitely associating this stem and conesnbsp;with a true Equisetites. We may, however, adhere to thisnbsp;generic title until more satisfactory data are available.

This species is chosen as an example of a French Equisetites of Permian age. It was recently founded by Zeiller� on somenbsp;specimens of imperfect leaf-sheaths, and defined as follows;�

Sheaths spreading, erect, formed of numerous uniiierved coherent leaves, convex on the dorsal surface, spatulate in form, 5�6 cm. in lengthnbsp;and 2�3 mm. broad at the base, and 5�10 mm. broad at the apex,nbsp;rounded at the distal end.

The specimen shown in fig. 58, A, represents part of a flattened sheath, the narrower crenulated end being the base of thenbsp;sheath. The limits of the coherent segments and the positionnbsp;of the veins are clearly marked. Zeiller�s description accuratelynbsp;represents the character of the sheaths. They agree closelynbsp;with an Equisetaceous leaf-sheath, but as I have alreadynbsp;pointed out, we cannot feel certain that sheaths of this kindnbsp;were not originally attached to a Calamite stem.

The portion of a leaf-sheath and a diaphragm represented in fig. 57, B, agrees closely with Zeiller�s examples. This specimennbsp;is from the English Coal-Measures, but it is not advi,sable to

Fig. 58. A. Equisetites sqmtulatus, Zeill. Leaf-sheath. 4 nat. size. (After Zeiller.)

L. Annularia stellata (Schloth.). Leaf-sheath. Slightly enlarged. (After Potoni�.)

F. nbsp;nbsp;nbsp;E. lateralis, Phill. From a specimen in the Scarborough Museum.

attempt any specific diagnosis on such fragmentary material. It is questionable, indeed, if these detached fossil leaf-sheathsnbsp;should be designated by specific names. Another similar formnbsp;of sheath, hardly distinguishable from Zeiller�s species, has recently been described by Potonie from the Permian (Rothlie-gende) of Thuringia.

The sheaths consist of linear segments fused laterally as in Equisetum. In some specimens the component parts of thenbsp;sheath are more or less separate from one another, and innbsp;this form they are apparently identical with the leaves ofnbsp;Calamites {Calamitina) varians, Sternb. The example shown innbsp;fig. 58, E is probably a young leaf-sheath ; the segments are fused,nbsp;and each is traversed by a single vein represented by a darknbsp;line in the figure. The regular crenulated lower margin is thenbsp;base of the sheath, and corresponds to the upper portion ofnbsp;fig. 58, A. This species affords, therefore, an interesting illustration of the difficulty of sepai�ating Equisetites leaves fromnbsp;those of true Calamites. Potonie has suggested that the leaf-sheath of a young Calamite might well be split up into distinctnbsp;linear segments as the result of the increase in girth of thenbsp;stem.

Other Palaeozoic species of Equisetites have been recorded, but with one exception these need not be dealt with, as they donbsp;not add anything to our knowledge of botanical importance.nbsp;The specimen described in the Flore de Gommentry as Equisetites Monyi, by Renault and Zeiller^, differs from most of thenbsp;other Palaeozoic species of Equisetites, in the fact that we havenbsp;a stem with short internodes bearing a leaf-sheath at eachnbsp;node divided into comparativeh- long and distinct teeth.nbsp;This species presents a close agreement with specimens of Calamitina, but Renault and Zeiller consider that it is genericallynbsp;distinct. They suggest that the English species, originally

described and figured by Lindley and Hutton^ as Hippurites giganten, and now usually spoken of as Calamitina, should benbsp;named Equisetites. It would probably be better to adopt thenbsp;name Calamitina for the French species. The type-specimennbsp;of this species is in the Natural History Museum, Paiis.

When we pass from the Permian to the Triassic period, we find large casts of very modern-looking Equisetaceous stemsnbsp;which must clearly be referred to the genus Equisetites. Thenbsp;portion of a stem represented in fig. 59 known as Equisetitesnbsp;platyodon Brongn.^ affords an example of a Triassic Equisetaceous stem with a clearly preserved leaf-sheath. Thenbsp;stem measures about 6 cm. in diameter. One of the oldestnbsp;known Triassic species is Equisetites MougeotC (Brongn.) fromnbsp;the Bunter series of the Vosges.

�he Keuper species E. arenaceus is, however, more completely known. The specimens referred to this species are very striking fossils; they agree in all external charactersnbsp;with recent Horse-tails hut greatly exceed them in dimensions.

This plant has been found in the Triassic rocks of various parts of Germany and France; it occurs in the Lettenkohlnbsp;group (Lower Keuper), as well as in the Middle Keuper ofnbsp;Stuttgart and elsewhere. The species may be defined asnbsp;follows:�

Rhizome from 8�14 cm. in diameter, with short internodes, bearing lateral ovate tubers. Aerial shoots from 4�12 cm. innbsp;diameter, bearing whorls of branches, and leaf-sheaths made upnbsp;of 110�120 coherent uni-nerved linear segments terminating innbsp;an apical lanceolate tooth. Strobiii oval, consisting of crowdednbsp;sporangiophores with pentagonal and hexagonal peltate terminations.

The casts of branches, rhizomes, tubers, buds and cones enable us to form a fairly exact estimate of the size andnbsp;genera] appearance of this largest fossil Hotse-tail. Thenbsp;Strassburg Museum contains many good examples of thisnbsp;species, and a few specimens may be seen in the Britishnbsp;Museum. In the Ecole des Mines, Paris, there are somenbsp;exceptionally clear impressions of cones of this species from anbsp;lignite mine in the Vosges.

It is estimated that the plant reached a height of 8 to 10 meters, about equal to that of the tallest recent species ofnbsp;Equisetum, but iu the diameter of the stems the Triassic plantnbsp;far exceeded any existing species.

It is interesting to determine as far as possible, in the absence of petrified specimens, if this Keuper species increasednbsp;in girth by means of a cambium. There are occasionally foundnbsp;sandstone casts of the pith-cavity which present an appearancenbsp;very similar to that of Calamitean medullary casts! The

nodes are marked by comparatively deep constrictions, which probably represent the projecting nodal wood. The surface ofnbsp;the casts is traversed by regular ridges and grooves as in annbsp;ordinary Calamite, and it is probable that in Equisetitesnbsp;arenaceus, as in Calamites, these surface-features are the impression of the inner face of a cylinder of secondary woodnbsp;{cf. p. 310). Excellent figures of this species of Equisetites arenbsp;given by Schimper in his Atlas of fossil plants', also by Schimpernbsp;and Koechlin-Schlumberger^, and by Schoenlein and Schenks

This species, which is by far the best known British Equisetites, was founded by Brongniart�* on some specimensnbsp;from the Lower Oolite beds of the Yorkshire coast. Casts ofnbsp;stems are familiar to those who have collected fossils on thenbsp;coast between Whitby and Scarborough; they are often foundnbsp;in an erect position in the sandstone, and are usually describednbsp;as occurring in the actual place of growth. As previouslynbsp;pointed out (p. 72), such stems have generally been deposited by water, and have assumed a vertical positionnbsp;(fig. 11). Young and Bird'' figured a specimen of this speciesnbsp;in 1822, and in view of its striking resemblance to the sugarcane, thej^ regarded the fossil as being of the same family asnbsp;Saccharum officinariim, if not specificall}^ identical.

A specimen was described by K�nig� in 1829, from the Lower Oolite rocks of Brora in the north of Scotland under thenbsp;name of Oncylogonatum carhonariurn, but Brongniart'' pointednbsp;out its identity with the English species Equisetites columnaris.

Our acquaintance with this species is practically limited to the casts of stems. A typical stem of E. columnaris measuresnbsp;8 to 6 cm. in diameter and has fairly long internodes. The

largest stem in the British Museum collection has internodes about 14 cm. long and a diameter of about 5 cm. In some cases the stem casts show irregular lateral projections innbsp;the neighbourhood of a node, but there is no evidence that thenbsp;aerial shoots of this species gave off verticils of branches. Innbsp;habit E. columnaris probably closely resembled such recentnbsp;species as Equisetmi hiemale L., E. trachyodon A. Br. andnbsp;others.

The stems often show a distinct swelling at the nodes; this may be due, at least in part, to the existence of transversenbsp;nodal diaphragms which enabled the dead shoots to resistnbsp;contraction in the region of the nodes. The leaf-sheathsnbsp;consist of numerous long and narrow segments often truncatednbsp;distally, as in fig. 58, B, and as in the sheath of such a recentnbsp;Horse-tail as E. ramosissimum shown in fig. 58, G. In somenbsp;specimens one occasionally finds indications of delicate acuminate teeth extending above the limits of a truncated sheath.nbsp;Brongniart speaks of the existence of caducous acuminate teethnbsp;in his diagnosis of the species, and the example representednbsp;in fig. 58, B, demonstrates the existence of such deciduousnbsp;appendages. There is a very close resemblance between thenbsp;fossil sheath of fig. 58, B, with and without the teeth, andnbsp;the leaf-sheath of the recent Equisetum in fig. 58, C. Innbsp;some specimens of E. columnaris in which the cast is coverednbsp;with a carbonaceous film, each segment in a leaf-sheath isnbsp;seen to be slightly depressed in the median portion, whichnbsp;is often distinctly marked by numerous small dots, the edgesnbsp;of the segment being flat and smooth. The median regionnbsp;is that in which the stomata are found and on which depositsnbsp;of silica occur.

Bunbury� proposed the name Calamites Beani for some fossil stems from the Lower Oolite beds of the Yorkshire coast,nbsp;which Bean had previously referred th in unpublished notes asnbsp;�. giganteus. The latter name was not adopted by Bunbury

on account of the possible confusion between this species and the Palaeozoic species Calamites gigas Brong. The genericnbsp;name Calamites must be replaced by Equisetites now that wenbsp;are familiar with more perfect specimens which demonstratenbsp;the Equisetean characters of the plant.

Schimper^ speaks of this species as possibly the pith-cast of Equisetites columnaris, but his opinion cannot be maintained; the species first described by Bunbury has considerablynbsp;larger stems than those of E. columnaris. It is not impossible,nbsp;however, that E. columnaris and E. Beani may be portionsnbsp;of the same species. The chief difference between these formsnbsp;is that of size; but we have not sufficient data to justify' thenbsp;inclusion of both forms under one name. Zigno'^, in his worknbsp;on the Oolitic Flora, figures an imperfect stem cast of E. Beaninbsp;under the name of Calamites Beani, but the species has

received little attention at the hands of recent writers. In 1886 Starkie Gardner^ figured a specimen which was identified bynbsp;Williamson as an example of Bunbury�s species; but the latternbsp;pointed out the greater resemblance, as regards the externalnbsp;appearance of the Jurassic stem, to some of the recent arborescent Gramineae^ than to the Equisetaceae. Williamson, withnbsp;his usual caution, adds that such appearances have very littlenbsp;taxonomic value. Fig. 60 is reproduced from the block usednbsp;by Gardner in his memoir on Mesozoic Angiosperms; he quotesnbsp;the specimen as possibly a Monocotyledonous stem. The fossilnbsp;is an imperfect cast of a stem showing two clearly markednbsp;nodal regions, but no trace of leaf-sheaths. A recent examination of specimens in the museums of Whitby, Scarborough,nbsp;York and London has convinced me that the plant named bynbsp;Bunbury Calamites Beani is a large Equisetites. As a rule thenbsp;specimens do not show any indications of the leaf-sheaths, butnbsp;in a few cases the sheaths have left fairly distinct impressions.

In the portion of stem shown in fig. 61 the impressions of the leaf segments are clearly mai�ked. This specimen af^rdsnbsp;much better evidence of the Equisetaceous character of thenbsp;plant than those which are simply internal casts. The narrownbsp;projecting lines extending upwards from the nodes in thenbsp;figured specimen probably represent the divisions between thenbsp;several segments of each leaf-sheath.

In the museums of Whitby and Scarborough there are some long specimens, in one case 4�cm. in length, and 33 cm. innbsp;circumference, which are probably casts of the broad pith-cavity.nbsp;These casts are often transversely broken across at the nodes,nbsp;so that they consist of three or four separate pieces which fitnbsp;together by clean-cut faces. This manner of occurrence is mostnbsp;probably due to the existence of large and resistant nodal diaphragms which separated the sand-casts of adjacent internodes.nbsp;In the York museum there are some large diaphragms, 10 cm.nbsp;in diameter, preserved separately in a piece of rock containingnbsp;a cast of Equisetites Beani. The nodal diaphragms of some ofnbsp;the Carboniferous Calamites were the seat of cork development�,

and it may be that the frequent preservation of Equisetaceous diaphragms in Triassic and Jurassic rocks is due to the protection afforded by a corky investment.

The stem shown in fig. 62 appears to be a portion of a shoot of E. Beani not far from its apical region. From thenbsp;lower nodes there extend clearly marked and regular lines ornbsp;slight grooves tapering gradually towards the next higher node;nbsp;these are no doubt the impressions of segments of leaf-sheaths.nbsp;The sheaths themselves have been detached and only theirnbsp;impressions remain. The flattened bands at the node of thenbsp;stem in fig. 60, and shown also in fig. 61, mark the place ofnbsp;attachment of the leaf-sheaths. On some of these nodal bandsnbsp;one is able to recognise small scars which are most likely thenbsp;casts of outgoing leaf-trace bundles.

Some of the internal casts of this species are marked by numerous closely arranged longitudinal lines, which are probablynbsp;the impressions of the inner face of a central woody cylinder.nbsp;In the smaller specimen shown in fig. 62 we have the apical

portion of a shoot in which the uppermost internodes are in an unexpanded condition.

It is impossible to give a satisfactory diagnosis of this species without better material. The plant is characterisednbsp;chiefly by the great breadth of the stem, and by the possessionnbsp;of leaf-sheaths consisting of numerous long and narrow segments. Equisetites Beani must have almost equalled in sizenbsp;the Triassic species, E. arenaceus, described above.

This species is described at some length as affording a useful illustra tion of the misleading character of certain features which

r;:i

Eig. 63. Equisetites lateralis Phill. From a specimen in the British Museum. Slightly reduced.

are entirely due to methods of preservation. The specific name was proposed by Phillips in his first edition of the Geology of

the Yorkshire Coast for some very imperfect stems from the Lower Oolite rocks near Whitbyk The choice of the termnbsp;lateralis illustrates a misconception; it was given to the plantnbsp;in the belief that certain characteristic wheel-like marks onnbsp;the stems were the scars of branches. Lindley and Hutton^nbsp;figured a specimen of this species in their Fossil Flora, andnbsp;quoted a remark by � Mr Williamson junior � (afterwards Prof.nbsp;Williamson) that the so-called scars often occur as isolatednbsp;discs in the neighbourhood of the stems. Bunbury� describednbsp;an example of the same species with narrow spreading leavesnbsp;like those of a Palaeozoic AsterophyHites, and proposed thisnbsp;generic name as more appropriate than Equisetites. In all probability the example shown in fig. 63 is that which Bunburynbsp;described. It is certainly the same as one figured by Zignm* asnbsp;Galamites lateralis in his Flora fossilis formationis Oolithicae.

This specimen illustrates a further misconception in the diagnosis of the species. The long linear appendages spreadingnbsp;from the nodes are, I believe, slender branches and not leaves ;nbsp;they have not the form of delicate filmy markings on the rocknbsp;face, but are comparatively thick and almost woody in appearance. The true leaves are distinctly indicated at the nodes,nbsp;and exhibit the ordinary features of toothed sheaths.

Heer� proposed to transfer Phillips� species to the genus Phyllotheca, and Schimper� preferred the generic term Schizo-neura. The suggestion for the use of these two names wouldnbsp;probably not have been made had the presence of the Equisetuninbsp;sheaths been recognised.

The circular depressions a short distance above each node are the � branch scars � of various writers. Schimper suggestednbsp;that these radially marked circles might be displaced nodalnbsp;diaphragms. Andrae^ figured the same objects in 1853nbsp;but regarded them as branch scars, although in the specimen he describes, there are several of them lying apart from

o Schimper (69) p. 284. Vide also Nathorst (80) p. 54. �� Andrae (53) PI. vi. figs. 1�5.

the stems, and to one of them is attached a portion of a leaf-sheath. Solms-Laubach ^ points out that the internodalnbsp;position of these supposed scars is an obvious difficulty; wenbsp;should not expect to find branches arising from an internode.nbsp;After referring to some specimens in the Oxford museum, henbsp;adds�� In presence of these facts the usual explanation of thesenbsp;structures appears to me, as to Heer, very doubtful....We arenbsp;driven to the very arbitrary assumption that they represent thenbsp;lowest nodes of the lateral branches which were inserted abovenbsp;the line of the nodes of the stem.� Circular discs similar tonbsp;those of E. latej'alis have been found in the Jurassic rocks ofnbsp;Siberia� and elsewhere. There are one or two examples ofnbsp;such discs from Siberia in the British Museum. If the nodalnbsp;diaphragms were fairly hard and stout, it is easy to conceivenbsp;that they might have been pressed out of their original positionnbsp;when the stems were flattened in the process of fossilisation. Itnbsp;is not quite clear what the radial spoke-like lines of the discsnbsp;are due to; possibly they mark the position of bands of morenbsp;resistant tissue or of outgoing strands of vascular bundles.nbsp;A detached diajihragm is seen in fig. 64 C; in the centre itnbsp;consists of a flat plate of tissue, and the peripheral region isnbsp;traversed by the radiating lines. In the stem of fig. 64, Anbsp;the deeply divided leaf-sheaths are clearly seen, and an imperfect impression of a diaphragm is preserved on the face ofnbsp;the middle internode. In fig. 64 B a flattened leaf-sheath isnbsp;shown with the free acuminate teeth fused basally into anbsp;continuous collarquot;. The short piece of stem of Equisetitesnbsp;lateralis shown in fig. 58, F, shows how the free teeth may benbsp;outspread in a manner which bears some resemblance to thenbsp;leaves of Fhyllotheca, but a comparison with the specimensnbsp;already described, and a careful examination of this specimennbsp;itself, demonstrate the generic identity of the species withnbsp;Equisetites. The carbonaceous film on the surface of suchnbsp;stems as those of fig. 58, F, and 64, A, shows a characteristicnbsp;shagreen texture which may possibly be due to the presence ofnbsp;, silica in the epidermis as in recent Horse-tails.

There is another species of Equisetites, E. Mimsteri, Schk., from a lower geological horizon which has been compared with

Fie. 64. Equisetites lateralis Phill. A. Part of a stem showing leaf-sheaths and an imperfect diaphragm. B. A single flattened leaf-sheath. C. Anbsp;detached nodal diaphragm. From a specimen in the York Museum.nbsp;Slightly reduced.

E. lateralis, and lends support to the view that the so-called branch-scars are nodal diaphragms'. This species also affordsnbsp;additional evidence in favour of retaining the generic namenbsp;Equisetites for Phillips� species. Equisetites Mihnsteri is a typicalnbsp;Rhaetic plant; it has been found at Beyreuth and Kuhnbach,nbsp;as well as in Switzerland, Hungary and elsewhere. A specimennbsp;of Equisetites originally described by Buckman as E. Brodii-,nbsp;from the Lower Lias of Worcestershire, may possibly be identical with E. M�nsteri. The leaf-sheaths of this Rhaetic speciesnbsp;consist of broad segments prolonged into acuminate teeth; some

1 Since this was written I have found a specimen of Equisetites lateralis in the Woodwardian Museum, in which a diaphragm like that in fig. 64, C, occursnbsp;in the centre of a flattened leaf-sheath similar to that of fig. 64, B.

of the examples figured by Schenk^ show clearly marked impressions of displaced nodal diaphragms exactly as in E. lateralis. Another form, Equisetum rotifernm described by Tenison-Woods ^nbsp;from Australia, is closely allied to, or possibly identical withnbsp;E. lateralis.

This species of Equisetites is fairly common in the Wealden beds of the Sussex coast near Hastings, and also in Westphalia.

Fig. 65. Equisetites Burchardti Dunk. Showing a node with two tubers and a root. From a specimen in the British Museum. Nat. size.

It is characterised by having long and slender internodes, bearing at the nodes leaf-sheaths with five or six pointed segments, and by the frequent formation of branch-tubers. Thesenbsp;tuberous branches closely resemble those which are formed onnbsp;the underground shoots of Equisetum arvense L., E. sylva-ticum L. and others; they occur either singly or in chains^.nbsp;In the specimen shown in the figure the left-hand tuber isnbsp;remarkably well preserved, its surface is somewhat sunk andnbsp;shrivelled, and the apex is surrounded by a nodal leaf-sheath.nbsp;A thin branched root is given off just below the point ofnbsp;insertion of the oval tuber.

^ Tenison-Woods (83), PI. vi. figs. 5 and 6. Specimen no. T. 3358 in the British Museum.

examples of tubers as this Wealden plant. By some of the earlier wi�iters the detached tubers of E. Burchardti werenbsp;described as fossil seeds under the name Carpolithus.

Fig. 66. Equisetites Yokoyamae Sew. From specimens in the British Museum. Nat. size.

The specimens shown in fig. 66 have been referred to another species, E. Yokoyamae Sew.'; they were obtained fromnbsp;the Wealden beds of Sussex, but according to Mr Rufford,nbsp;who discovered them, the smaller tubers of this species are notnbsp;found in association with those of E. Burchardti. The stemsnbsp;are very narrow and the tubers have a characteristic ellipticalnbsp;form; the species is of little value botanically, but it affordsnbsp;another instance of the common occurrence of these tuberousnbsp;branches in the Wealden Bquisetums.

Similar fossil tubers, on a much larger scale, have been found in association with the Triassic Equisetites arenaceus;nbsp;with E. Parlatori Heer^ a Tertiary species from Switzerland,nbsp;and with other Mesozoic and Tertiary stems. E. Burejensis^,nbsp;described by Heer from the Jurassic rocks of Siberia, bears anbsp;close resemblance to the Wealden species.

The description of the above species by no means exhausts the material which is available towards a history of fossil

Equisetums. . The examples which have been selected may serve to illustrate the kind of specimens that are usually metnbsp;with, as well as some of the possible sources of error whichnbsp;have to be borne in mind in the description of species.

Such Tertiary species as have been recorded need not be considered: they furnish us with no facts of particular interestnbsp;from a morphological point of view. The wide distribution ofnbsp;Equisetites, especially during the Jurassic period, is one of thenbsp;most interesting lessons to be learnt from a review of the fossilnbsp;forms. No doubt a detailed comparison of the several speciesnbsp;from different parts of the world would lead us to reduce thenbsp;number of specific names; and at the same time it wouldnbsp;emphasize the apparent identity of fossils which have beennbsp;described from widely separated latitudes under different names.

Specimens of Equisetites are occasionally found in plantbearing beds apart from the other members of a Flora; this isolated manner of occurrence suggests that the plant grewnbsp;in a different station from that occupied by Cycads and othernbsp;elements of the vegetation tnbsp;nbsp;nbsp;nbsp;^

A selection of Triassic and Jurassic species arranged in a tabular form demonstrates the wmrld-wide distribution of thisnbsp;persistent type of plant

The generic name Phyllotheca was proposed by Brongniart� in 1828 for some small fossil stems from the Hawkesbury river,nbsp;near Port Jackson, Australia. The stems of this genus arenbsp;divided into nodes and internodes and possess leaf-sheaths asnbsp;in Equisetum, but Phyllotheca differs from other Equisetaceousnbsp;plants in the form of the leaves and in the character of itsnbsp;sporophylls. We may define the genus as follows:�

Plants resembling in habit the recent Equisetums. Stems simple or branched, divided into distinct nodes and internodes,

the latter marked by longitudinal ridges and grooves; from the nodes are given off leaf-sheaths consisting of linear-lanceolatenbsp;uninerved segments coherent basally, but having the form ofnbsp;free narrow teeth for the greater part of their length. Thenbsp;long free teeth are usually spread out in the form of a cup andnbsp;not adpressed to the stem, the tips of the teeth are often incurved.

The sporangia are borne on peltate sporangiophores attached to the stem between whorls of sterile leaves.

Our knowledge of Phyllotheca is unfortunately far from complete. The chief characteristic of the vegetative shootsnbsp;consists in the cup-like leaf-sheaths; these are divided up intonbsp;several linear segments, which differ from the teeth of annbsp;Equisehim leaf-sheath in their greater length and in theirnbsp;more open and spreading habit of growth. The large loosenbsp;sheaths of the fertile shoots of some recent Horse-tails hearnbsp;a certain resemblance to the sheaths of Phyllotheca. Thenbsp;diagnosis of the fertile shoots is founded principally on somenbsp;Permian specimens of the genus described by Schmalhausennbsp;from Russia^ and redescribed more recently by Solms-Laubach^.nbsp;Prof Zeiller� has, however, lately received some examples ofnbsp;Phyllotheca from the Coal-Measures of Asia Minor which bearnbsp;strobili like those of the genus Annularia, a type which is dealtnbsp;with in the succeeding chapter. A description of a few speciesnbsp;will serve to illustrate the features usually associated with thisnbsp;generic type, as well as to emphasize the unsatisfactory state ofnbsp;our knowledge as to the real significance of such supposednbsp;generic characteristics.

There are a few fossil stems from Permian rocks of Siberia, from Jurassic strata in Italy, and from Lower Mesozoicnbsp;and Permo-Carboniferous beds in South America, South Africa,nbsp;India and Australia which do not conform in all points to thenbsp;usually accepted definition of Equisetites, and so justify theirnbsp;inclusion in an allied genus. On the other hand there arenbsp;numerous instances of stems or branches which have been

referred to PhijllotJieca on insufficient grounds. Our knowledge of this Equisetaceous plant has recently been extended by Zeillei'k who has recorded its occurrence in the Coal-Measures of Asia Minor associated with typical Uppernbsp;Carboniferous plants. The same author^ has also broughtnbsp;forward good evidence for the Permian age of the bedsnbsp;in Siberia and Altai, where Phyllotheca has long beennbsp;known. It is true that Zigno�s species of the genus occurs innbsp;Italian Jurassic rocks, but on the whole it would seem thatnbsp;this genus is rather a Permian than a Jurassic tj^pe. Thenbsp;species which Zeiller describes under the name Phyllothecanbsp;Rallii from the Coal-Measures of Herakleion (Asia Minor)nbsp;shows some points of contact with Anmdaria. It is muchnbsp;to be desired, however, that we might learn more as to thenbsp;reproductive organs of this member of the Equisetales; untilnbsp;we possess a closer acquaintance with the fructification wenbsp;cannot hope to arrive at anj' satisfactory conclusion as to thenbsp;exact position of the genus among the Calamarian and Equisetaceous forms. M. Zeiller� informs me that his specimefis ofnbsp;P. Rallii, which are to be fully described in a forthcoming work,nbsp;include fossil strobili resembling those of Anmdaria radiata.nbsp;The verticils of linear leaves fused basally into a sheath agreenbsp;in appearance with the star-like leaves of Anmdaria, but innbsp;Phyllotheca Rallii the segments appear to spread in all directionsnbsp;and are not extended in one plane as in the typical Anmdaria^.

In an account of some fossil plants collected by Tchikatcheff in Altai, Goppert� describes and figures two imperfect stems ofnbsp;an Equisetum-like plant. Owing to the apparent absence ofnbsp;nodal lines on the surface of the stem the generic name Anarthro-canna is proposed for the fossils ; and the manner in which thenbsp;main axis appears to break up into slender branches suggestednbsp;the specific name deliquescens. Schmalhau.sen� afterwards

' Zeiller (95�). nbsp;nbsp;nbsp;2 lud. (96).nbsp;nbsp;nbsp;nbsp;� Letter, July 30, 1897.

� Goppert (45) p. 379, Pl.xxv. figs. 1, 2. nbsp;nbsp;nbsp;� Schmalhausen (79) p. 12.

recognised the generic identity of G�ppert�s fragments with the Indian and Australian stems referred to the genus Phyllo-theca by McCoy ^ and Bunbury�.

Stem reaching a diameter of 2�3 cm. with internodes as much as 4 cm. long, the surface of which is traversed bynbsp;longitudinal ridges and grooves which are continuous and notnbsp;alternate at the nodes. Branches arise in verticils from thenbsp;nodes. The leaves have the form of funnel-shaped sheaths splitnbsp;up into narrow and spreading linear segments, each of which isnbsp;traversed by a median vein. The fertile' shoot terminates innbsp;a loose strobilus bearing alternating whorls of sterile bracts andnbsp;sporangiophores.

The specimens on which this diagnosis is founded are for the most part fragments of sterile branches. Some of thesenbsp;present the appearance of Calamitean stems in which thenbsp;ridges and grooves continue in straight lines from one internode to the next. Similar stem-casts have been referred bynbsp;some writers to the allied genus Schizoneura, and it wouldnbsp;appear to be a hopeless task to decide with certainty undernbsp;which generic designation such specimens should be described.nbsp;The portion of stem shown in fig. 67 affords an example ofnbsp;an Eqnisetaceous plant, probably in the form of a cast of anbsp;hollow pith, which might be referred to either Phyllotheca ornbsp;Schizoneura. The specimen was found in certain Southnbsp;African rocks which are probably of Permo-Carboniferous age�.nbsp;It agrees closely with some stems from India described bynbsp;FeistmanteP as Schizoneura gondwanensis, and it also resemblesnbsp;equally closely the Australian specimens referred by Feist-mantel� to Phyllotheca australis and some stems of Phyllothecanbsp;indica figured by Bunbury�.

The longitudinal ridges and grooves shown in fig. 67 probably represent the broad medullary rays and the projecting wedges of secondary wood surrounding a large hollow

pith, as in Calamites. In the Calamitean casts the ridges and grooves of each internode usually alternate in position withnbsp;those of the next, as in Equisetum (fig. 54, A), but in Phyl-lotheca, Schizoneura and Archaeocalamites there is no suchnbsp;reo-ular alternation at the nodes of the internodal vascularnbsp;strands.

Fig. 67. PhylUtlieca ? ^ nat. size. From a South African specimen of Permo-Carboniferous age in the British Museum.

In Phyllotheca and Schizoneura there are no casts of � infra-nodal canals � below each nodal line, but these are by no means always found in true Calamites. It is therefore practicallynbsp;impossible to determine the generic position of such fossils asnbsp;that shown in fig. 67 without further evidence than is affordednbsp;by leafless casts.

described by Schmalhausen in which a branch bears clusters of sporangiophores, alternating with verticils of sterile bracts.nbsp;The sporangiophores appear to have the form of stalked peltatenbsp;appendages bearing sporangia, very similar to the sporangiophores of Equisetum. Solms-Laubach* has examined the best ofnbsp;Schmalhausen�s specimens, and a carefully drawn figure of onenbsp;of the fertile branches is given in his Fossil Botany.

The significance of this manner of occurrence of sporangiophores and whorls of sterile bracts on the fertile branch will be better understood after a description of the strobilus ofnbsp;Catamites. In Phyllotheca the sporangiophores appear to havenbsp;been given off in whorls, which were separated from one anothernbsp;by whorls of sterile bracts, whereas in Equisetum there are nonbsp;sterile appendages associated with the sporangiophores of thenbsp;strobilus, with the exception of the annulus at the base of thenbsp;cone. Heer^ first drew attention to the fact that in Phyllothecanbsp;we have a form of strobilus or fertile shoot to a certain extentnbsp;intermediate in character between Equisetum and Catamites.

In abnormal fertile shoots of Equisetum, sporophylls occasionally occur above and below a sterile leaf-sheath. Potonid^ has figured such an example in which an apical strobilus isnbsp;succeeded at a lower level by a sterile leaf-sheath, and this againnbsp;by a second cluster of sporophylls. As Potoni� points out, thisnbsp;alternation of fertile and sterile members affords an interesting-resemblance between Phyllotheca and Equisetum. It suggestsnbsp;a partial reversion towards the Calamitean type of strobilus.

This species of Phyllotheca from the Lower Oolite rocks of Italy is known only in the form of sterile branches. The leavesnbsp;are fused basally into an open cup-like sheath which is dissectednbsp;into several spreading and incurved linear segments. Thenbsp;internodes are striated longitudinally; they are about 2 mm.nbsp;in diameter and 10 mm. in length.

The specimen represented in fig. 68, A, was originally described by the Italian palaeobotanist Zigno'; it serves tonbsp;illustrate the points of difference between this genus and thenbsp;ordinary Equiseium. The open and spreading sheaths claspingnbsp;the nodes and the erect solitary branches give the plant anbsp;distinctive appearance.

C. nbsp;nbsp;nbsp;Phyllotheca itiiHca, Bunb. Part of a leaf-sheath. From a speci

Sir Charles Bunbury^ described several imperfect specimens from the Nagpur district of India under this name, but henbsp;^ Zigno (56) PI. vii. p. 59.nbsp;nbsp;nbsp;nbsp;^ Bunbury (61).

expressed the opinion that it was not clear to him if the plant was specifically distinct from the Phyllotheca australis Brongn.nbsp;previously recorded from New South Wales. FeistmanteBnbsp;subsequently described a few other Indian specimens, but didnbsp;not materially add to our knowledge of the genus. Bunbury�snbsp;specimens were obtained from Bharat wad a in Nagpur, in bedsnbsp;belonging to the Damuda series of the Lower Gondwana rocks,nbsp;usually regarded as of about the same age as the Permian rocksnbsp;of Europe.

Phyllotheca indica is represented by broken and imperfect fragments of leaf-bearing stems. The species is thus diagnosednbsp;by Bunbury:��Stem branched, furrowed; sheaths lax, somewhat bell-shaped, distinctly striated; leaves narrow linear,nbsp;with a strong and distinct midrib, widely spreading and oftennbsp;recurved, nearly twice as long as the sheaths.� An examinationnbsp;of the specimens in the Museum of the Geological Society ofnbsp;London, on which this account was based, has led me to thenbsp;opinion that it is practically impossible to distinguish thenbsp;Indian examples from P. australis described by Brongniart^nbsp;from New South Wales. The few specimens of the latternbsp;species which I have had an opportunity of examining bearnbsp;out this view. In the smaller branches the axis of P. indicanbsp;is divided into rather short internodes on which the ridges andnbsp;grooves are faintly marked. In the larger stems the ridges andnbsp;grooves are much more prominent, and continuous in directionnbsp;from one internode to the next; a few branches are given offnbsp;from the nodes of some of the specimens. The leaves are notnbsp;very well preserved; they consist of a narrow collar-like basalnbsp;sheath divided up into numerous long and narrow segments,nbsp;which are several times as long as the breadth of the sheath,nbsp;and not merely twice as long as Bunbury described them. Eachnbsp;leaf-sheath has the form of a very shallow cup-like rim claspingnbsp;the stem at a node, with long free spreading segments whichnbsp;are often bent back in their distal region. The general habitnbsp;of the leafy branches appears to be identical with that ofnbsp;P. australis as figured by McCoy.

Prof. Zeiller informs me that in the type-specimen on which Brongniart founded the species, P. australis, the sheath appearsnbsp;to be closely applied to the stem with a verticil of narrownbsp;spreading segments radiating from its margin. It may be,nbsp;therefore, that in the Australian form there was not such annbsp;open and cup-like sheath as in P. indica', but it would benbsp;difficult, without better material before us, to feel confidence innbsp;any well marked specific distinctions between the Indian andnbsp;Australian Phyllothecas.

On the broader stems, such as that of fig. 67, we have clearly marked narrow grooves and broader and slightly convexnbsp;ridges, which present an appearance identical with that of somenbsp;Calamitean stems. In the specimen figured by Bunbury' in hisnbsp;PI. X, fig. 6, there is a circular depression on the line of thenbsp;node which represents the impression of the basal end of anbsp;branch; on the edges of the node there are indications of twonbsp;other lateral branches. The nature of this stem-cast pointsnbsp;uurnistakeably to a woody^ stem like that of Catamites. Thenbsp;precise meaning of the ridges and grooves on the cast isnbsp;described in the Chapter dealing with Calamitean plants.

Grand�Eury'^ in his monograph on the coal-basin of Gard, has recently described under the name of Galamocladus fron-dosm what he believes to be the leaf-bearing axes of anbsp;Calamitean plank The thicker branches are almost exactlynbsp;identical in appearance with the broader specimens of Phyllo-theca. The finer branches of Galamocladus bear cup-like leaf-sheaths which are divided into long and narrow recurvednbsp;segments (fig. 67, B), precisely as in Phyllotheca. These comparisons lead one to the opinion that the Phyllotheca ofnbsp;Australia and India may be a close ally of the Permo-Carboniferous Calamitean plants. The form of the leaf-whorlsnbsp;of Annidama (Calamarian leaf-bearing branches) and ofnbsp;Galamocladus is of the same type as in Phyllotheca; thenbsp;character of the medullary casts is also the same. The naturenbsp;of the fertile shoot of Phyllotheca described by Schmalhausennbsp;from Siberia, with its alternating whorls of sterile and fertilenbsp;leaves, is another point of agreement between this genus andnbsp;1 Bunbury (61).nbsp;nbsp;nbsp;nbsp;2 Grand�Eury (90) p. 221.

Calamitean plants. An Equisetaceous species has been described from the Newcastle Coal-Measures of Australia by Etheridge*nbsp;in which there are two forms of leaves, some of which closelynbsp;resemble those of Phyllotheca indica, while others are comparednbsp;with the sterile bracts of Cingularia, a Calamitean genusnbsp;instituted by Weiss I

When we turn to other recorded forms of Phyllotheca many of them appear on examination to have been placed in thisnbsp;genus on unsatisfactory grounds. Heer figures several stemnbsp;fragments from the Jurassic rocks of Siberia as P. Sibiricanbsp;Heer�, and it was the resemblance between this form and thenbsp;English Equisetites lateralis which led to the substitution ofnbsp;Phyllotheca for Equisetites in the latter species. Withoutnbsp;examining Heer�s material it is impossible to criticise hisnbsp;conclusions with any completeness, but several of his specimensnbsp;appear to possess leaf-sheaths more like those of Equisetum thannbsp;of Phyllotheca.

The frequent occurrence of isolated diaphragms and the comparatively long acuminate teeth of the leaf-sheath affordnbsp;obvious points of resemblance to Equisetites lateralis. Somenbsp;of the examples figured by Heer appear to be stem fragments,nbsp;with numerous long and narrow filiform leaves different innbsp;appearance from those of other specimens which he figures.nbsp;It may be that some of the less distinct pieces of stems arenbsp;badly torn specimens in which the internodes have beennbsp;divided into filiform threads. Heer also figures a fertile axisnbsp;associated with the sterile stems, and this does not, as Heernbsp;admits, show the alternating sterile bracts such as Schmalhausennbsp;has described. So far as it is possible to judge from an examination of Heer�s figures and a few specimens from Siberia innbsp;the British Museum�and this is by no means a safe basis onnbsp;which to found definite opinions�there appears to be littlenbsp;evidence in favour of separating the fossils described as Phyllotheca Sibirica from Equisetites. This Siberian form maynbsp;indeed be specifically identical with Equisetites lateralis Phill.

Jurassic and Upper Palaeozoic rocks in Australia. Some of these possess cup-like leaf-sheaths, and in the case of the thickernbsp;specimens they show continuous ridges and grooves on thenbsp;internodes, as well as a habit of branching similar to that innbsp;some of the Italian Phyllothecas. In some of the stems it isnbsp;however difficult to recognise any characters which justify thenbsp;use of the term Phyllotheca. A fragment figured by Tenison-Woods^ as a new species of Phyllotheca, P. carnosa, from Ipswich,nbsp;Queensland, affords an example of the worthless material onnbsp;which species have not infrequently been founded. The authornbsp;of the species describes his single specimen as a � faint impression�; the figure accompanying his description suggestsnbsp;a fragment of some coniferous branch, as Feistmantel hasnbsp;pointed out in his monograph on Australian plants.

It is important that a thorough comparative examination should be made of the various fossil Phyllothecas with a viewnbsp;to determine their scientific value, and to discover how far thenbsp;separation of Phyllotheca and Equisetites is legitimate in ep,chnbsp;case. There is too often a tendency to allow geographicalnbsp;distribution to decide the adoption of a particular generic name,nbsp;and this seems to have been especially the case as regardsnbsp;several Mesozoic and Palaeozoic Southern Hemisphere plants.

The geological and geographical range of Phyllotheca is a question of considerable interest, but as already pointed out itnbsp;is desirable to carefully examine the various records of thenbsp;genus before attempting to generalise as to the range of thenbsp;species. Phyllotheca is often spoken of as a characteristicnbsp;member of the Glossopteris Flora of the Southern Hemisphere,nbsp;and its geological age is usually considered to be Mesozoicnbsp;rather than Palaeozoic.

The plants included under this genus were originally designated by Brongniart� Convallarites and classed as Monocotyledons. Some years later Schimper and Mougeot� had

the opportunity of examining more perfect material from the Bunter beds of the Vosges, and proposed the new namenbsp;Schizoneura in place of Brongniart�s term, on the groundsnbsp;that the specimens were in all probability portions of Equi-setaceous stems, and not Monocotyledons. Our knowledge ofnbsp;this genus is very limited, but the characteristics are on thenbsp;whole better defined than in the case of Phyllotheca. Thenbsp;following diagnosis illustrates the chief features of Schizoneura.

Hollow stems with nodes and internodes as in Equisetum; the surface of the internodes is traversed by regular ridgesnbsp;and grooves, which are continuous and not alternate in theirnbsp;course from one internode to the next. The leaf-sheaths arenbsp;large and consist of several coherent segments ; the sheaths arenbsp;usually split into two or more elongate ovate lobes, and eachnbsp;lobe contains more than one vein. Fertile shoots are unknown.

Two of the best known and most satisfactory species are Schizoneura gondwanensis Feist, and S. paracloxa Schimp, andnbsp;Moug.nbsp;nbsp;nbsp;nbsp;'

This species is represented by numerous specimens from the Lower Gondwana rocks of India'; it is characterised bynbsp;narrow articulated stems which bear large leaf-sheaths at thenbsp;nodes. The sheaths may have the form of two large andnbsp;spreading elongate-oval lobes, each of which is traversed bynbsp;several veins (fig. 69, B), or the lobes may be further dissectednbsp;into long linear single-veined segments, as in fig. 69, A. It isnbsp;supposed that in the young condition each node bears a leaf-sheath consisting of laterally coherent segments which, asnbsp;development proceeds, split into two or more lobes. Feist-mantel records this species from the Talchir, Damuda andnbsp;Panchet divisions of the Lower Gondwana series of India; thesenbsp;divisions are regarded as equivalent to the Permo-Carboniferousnbsp;and Triassic rocks of Europe. The two specimens shown innbsp;fig. 69 are from the Lower Gondwana rocks of the Raniganjnbsp;Coal-field, India.

As already pointed out\ some of the specimens of flat and broader stems referred by Feistmantel to Schizoneura are

Fig. 69. Schizoneura yondwanensis Feist. (After Feistmantel; slightly reduced. )

identical in appearance with stems which have been described from India and elsewhere as species of Phyllotheca.

There are a few specimens of 8. gondwanensis in the British Museum, but the genus is poorly represented in European collections.

A similar plant was described in 1844 by Schimper and Mougeot^ from the Bunter rocks of the Vosges as Schizoneura paradoxa. This species bears a very close resemblancenbsp;to the Indian forms, and indeed it is difficult to point to anynbsp;distinction of taxonomic importance. Feistmantel considersnbsp;' ante, p. 284.nbsp;nbsp;nbsp;nbsp;^ Schimper and Mougeot (44) p. 50, Pis. xxiv.�xxvi.

that the European plant has rather fewer segments in the leaf-sheaths, and that the Indian plant had somewhat strongernbsp;stems. Both of these differences are such as might easil}^ benbsp;found on branches of the same species. It is, however, interestingnbsp;to notice the very close resemblance between the Lower Triasnbsp;European plant and the somewhat older member of the Glos-sopteris flora recorded from India and other regions, whichnbsp;probably once formed part of that Southern Hemispherenbsp;Continent which is known as Gondwana Land*.

CHAPTER X.

In order to minimise repetition and digression the following-account of the Calamarieae is divided into sections, under each of which a certain part of the subject is more particularly dealtnbsp;with. After a brief sketch of the history of our knowledge ofnbsp;Galamites, and a short description of the characteristics of thenbsp;genus, the morphological features are more fully considered.nbsp;A description of the most striking features of the better knownnbsp;Calamitean types is followed by a short discussion on thenbsp;question of nomenclature and classification, and reference isnbsp;made to the manner of occurrence of Galamites and to somenbsp;of the possible sources of error in identification.

In the following account of the Calamarieae the generic name Galamites is used in a somewhat comprehensive sense.nbsp;As previous writers have pointed out, it is probable that undernbsp;this generic name there may be included more than one type ofnbsp;plant worthy of generic designation. Owing to the variousnbsp;opinions which have been held by different authors, as to thenbsp;relationship and botanical position of plants now generally

included in the Calamarieae, there has been no little confusion in nomenclature. Facts as to the nature of the genus Cala-mites have occasionally to be selected from writings containingnbsp;many speculative and erroneous views, but the data at ournbsp;disposal enable us to give a fairly complete account of thenbsp;morphology of this Palaeozoic plant.

In the earliest works on fossil plants we find several figures of Ga.lamites, which are in most cases described as those of fossilnbsp;reeds or grasses. The Herharium diluvianum of Scheuchzer�nbsp;contains a figure of a Calamitean cast which is described asnbsp;probably a reed. Another specimen is figured by Volkmann^nbsp;in his Silesia suhterranea and compared with a piece of sugarcane. A similar flattened cast in the old Woodwardian collection at Cambridge is described by Woodward� as �part of anbsp;broad long flat leaf, appearing to be of some Iris, or rather annbsp;Aloe, but �tis striated without.� Schulzeone of the earliernbsp;German writers, figured a Calamitean branch bearing verticilsnbsp;of leaves, and described the fossil as probably the impression ofnbsp;an Equisetaceous plant. It has been pointed out by anothernbsp;German writer that the Equisetaceous character of Galamitesnbsp;was recognised by la3'men many years before specialists sharednbsp;this view.

One of the most interesting and important of all the older records of Galamites is that published by Suckow� in 1784.nbsp;Suckow is usually quoted as the author of the generic namenbsp;Galamites; he does not attempt any diagnosis of the plant, butnbsp;merely speaks of the specimens he is describing as � Calamiten.�nbsp;The examples figured in this classic paper are characteristicnbsp;casts from the Coal-Measures of Western Germany. Suckownbsp;describes them as ribbed stems, which were found in an obliquenbsp;position in the strata and termed by the workmen Jupiter�snbsp;nails (� Nagel �). Previous writers had regarded the fossilsnbsp;as casts of reeds, but Suckow correctly points out that thenbsp;ribbed character is hardl}.� consistent with the view that the

' Soheuehzer (1723), p. 19, PI. iv. fig. 1. 2 Volkmann (1720), p. 110, PI. xiii. fig. 7nbsp;� Woodward, J. (1728), Pt. ii. p. 10.

casts are those of reeds or grasses. He goes on to saj' that the material filling up the hollow pith of a reed would not havenbsp;impressed upon it a number of ribs and grooves such as occurnbsp;on the Calamites. He considers it more probable that thenbsp;casts are those of some well-developed tree, probably a foreignnbsp;plant. Equisetum giganteum L. is mentioned as a species withnbsp;which Calamites may be compared, although the stem of thenbsp;Palaeozoic genus was much larger than that of the recentnbsp;Horse-tail. The tree of which the Calamites are the castsnbsp;must, he adds, have jiossessed a ribbed stem, and the bark mustnbsp;also have been marked by vertical ribs and grooves on its innernbsp;face. It is clear, therefore, that Suckow inclined to the viewnbsp;that Calamites should be regarded as an internal cast of anbsp;woody plant. Such an interpretation of the fossils wasnbsp;generally accepted by palaeobotanists only a comparatively fewnbsp;years ago, and the first suggestion of this view is usuallynbsp;attributed to Germar, Dawes, and other authors who wrotenbsp;more than fifty years later than Suckow.nbsp;nbsp;nbsp;nbsp;''

One of the earliest notices of Calamites in the present century is by Steinhauerb who published a memoir in thenbsp;Transactions of the American Philosophical Society in 1818 onnbsp;Fossil reliquia of imknmun vegetables in the Carboniferous rocks.nbsp;He gives some good figures of Calamitean casts under thenbsp;generic name of Phytolithus, one of those general terms oftennbsp;used by the older writers on fossils. Among English authors,nbsp;Martin^ may be mentioned as figuring casts of Calamites, whichnbsp;he describes as probably grass stems. By far the best of thenbsp;earlier figures are those by Artis� in his Antediluvian Phytology.nbsp;This writer does not discuss the botanical nature of thenbsp;specimens beyond a brief reference to the views of earliernbsp;authors. Adolphe Brongniart^ writing in 1822, expresses thenbsp;opinion that the Calamites are related to the genus Equisetum,nbsp;and refers to M. de Candolle as having first suggested thisnbsp;view. In a later work Brongniart� includes species of Cu,la-mites as figured by Suckow, Schlotheim, Sternberg and Artis in

the family Equisetaceae. Lindley and Hutton � give several figures of Oalamites in their Fossil flora, but do not commitnbsp;themselves to an Equisetaceous affinity.

An important advance was made in 1835 by Cotta�, a German writer, who gave a short account of the internalnbsp;structure of some Calamite stems, which he referred to a newnbsp;genus Calamitea. The British Museum collection includes some

silicified fragments of the stems figured and described by Cotta in his Dendrolithen. Some of the specimens described by thisnbsp;author as examples of Calamitea have since been recognised asnbsp;members of another family.

In 1840 'Unger� published a note on the structure and affinities of Calamites, and expressed his belief in the closenbsp;relationship of the Palaeozoic plant and recent Horse-tails.

An important contribution to our knowledge of Calamites was supplied by Petzholdt�* in 1841. His main contention wasnbsp;the Equisetaceous character of this Palaeozoic genus. Thenbsp;external resemblance between Calamite casts and Equisetamnbsp;stems had long been recognised, but after Cotta�s account ofnbsp;the internal structure it was believed that the apparentnbsp;relation between Eqaisetum and Calamites was not confirmednbsp;by the facts of anatomy. Petzholdt based his conclusions onnbsp;cei�tain partially preserved Permian stems from Plauenschernbsp;Grund, near Dresden. Although his account of the fossils isnbsp;not accurate his general conclusions are correct. The specimens described by Petzholdt differ from the common Calamitenbsp;casts in having some carbonised remnants of cortical and woodynbsp;tissue. A transverse section of one of the Plauenscher Grundnbsp;fossils is shown in fig. 70. The irregular black patches werenbsp;described by Petzholdt as portions of cortical tissue, while henbsp;regarded the spaces as marking the position of canals like thenbsp;vallecular canals in an Equisetum. Our more complete knowledge of the structure of a Calamite stem enables us to

^ Cotta (50). I am indebted to Prof. Stenzel of Breslau for calling my attention to the fact that Cotta�s work appeared in 1832, but in 1850 the samenbsp;work was sold with a new title-page bearing this date.

correlate the patches in which no tissue has been preserved with the broad medullar}^ rays, which separated the wedge-shaped groups of xylem elements; the latter being morenbsp;resistant were converted into a black coaly substance, while thenbsp;cells of the medullary rays left little or no ti�ace in thenbsp;sandstone matrix. The thin black line, which forms the limit

of the drawing in fig. 70, external to the carbonised wood, no doubt marks the limit of the cortex, and the appendage indicatednbsp;in the lower part of the figure may possibly be an adventitiousnbsp;root. It is interesting to note that Unger* in 1844 expressed-the opinion, which we now know to be correct, that the coalynbsp;mass in the specimens described by Petzholdt represented thenbsp;wood, and that there was no proof of the existence of canals innbsp;the cortex as Petzholdt believed.

proposal which led to no little controvers3^ While retaining the genus Calamites for such specimens as possess a thin barknbsp;and a ribbed external surface, showing occasional branch-scarsnbsp;at the nodes, and having such characters as warrant theirnbsp;inclusion in the Equisetaceae, he proposes a second genericnbsp;name for other specimens which had hitherto been included innbsp;Calamites. The fossils assigned to his new genus Calaino-dendron are described as having a thick woody stem, and asnbsp;differing from Equisetum in their arborescent nature. Bron-gniart�s genus Galamodendron is made to include the plants fornbsp;which Cotta instituted the name Galamitea, and it is placednbsp;among the G^�mnosperms. This distinction between the Vascular Cryptogam Calamites and the supposed Gymnospei�mnbsp;Calamodendron is based on the presence of secondary' wood innbsp;the latter type of stem. The prominence formerly assigned tonbsp;the power of secondary thickening possessed by a plant as anbsp;taxonomic feature, is now known to have been the result ofnbsp;imperfect knowledge. The occurrence of a cambium layer andnbsp;the ability of a plant to increase in girth by the activity of anbsp;definite meristem, is a feature which some recent Vascularnbsp;Cryptogams^ share with the higher plants; and in former-ages many of the Pteridophytes possessed this method ofnbsp;growth in a striking degree.

Although Brongniart�s distinction between Calamites and Calarm,odendron has not been borne out by subsequent researches, the latter term is still used as a convenient designation for a special type of Calamitean structure. One of thenbsp;earliest accounts of the anatomj^ of Calamodendron stems isnbsp;by Mougeot'*, who published figures and descriptions of twonbsp;species, Calamodendron striatum and C. histriatum.

Some years later Goppert�, who was one of the greatest of the older palaeobotanists, instituted another genus, Arthro-pitys*, for certain specimens of silicified stems from thenbsp;Permian rocks of Chemnitz in Saxony, which Cotta hadnbsp;previously placed in his genus Galamitea under the name of

Calamitea bistriata^. Goppert rightly decided that the plants so named by Cotta differed in important histological charactersnbsp;from other species of Calamitea. The generic name Arthro-pitys has been widely adopted for a type of Calamitean stemnbsp;characterised by definite structural features. The great majority of the petrified Calamite stems ^found in the Englishnbsp;Coal-Measures belong to G�ppert�s Arthropitys.

The next proposal to be noticed is one by Williamson^ in 1868; he instituted the generic name Calamopitys for a fewnbsp;examples of English stems, which differed in the structure ofnbsp;the wood and primary medullary rays from previously recordednbsp;types. We have thus four names which all stand for genericnbsp;types of Calamitean stems. Of these Galamodendron andnbsp;Arthropitys are still used as convenient designations for stemsnbsp;with well-defined anatomical characters. The genus Calamitea.nbsp;is no longer in use, and Williamson�s name Calamopitys hadnbsp;previously been made use of by Unger� for plants which do notnbsp;belong to the Calamarieae. As it is convenient to have �omenbsp;term to apply to such stems as those which Williamson madenbsp;the t3^pe of Calamopitys, the name Arthrodendron is suggestednbsp;by my friend Dr Scott^ as a substitute for Williamson�s genus.

The twofold division of the Caiamites instituted by Bron-gniart has already been alluded to, and for many years it was generally agreed that both Pteridophytes and Gytnnospermsnbsp;were represented among the Palaeozoic fossils known as Caiamites. The work of Prof Williamson was largely instrumentalnbsp;in proving the unsound basis for this artificial separation; henbsp;insisted on the inclusion of all Caiamites in the Vascular Cryptogams, irrespective of the presence or absence of secondar}^nbsp;wood.nbsp;nbsp;nbsp;nbsp;degrees the adherents of Brongniart�s views

acknowledged the force of the English botanist�s contention. It is one of the many signs of the value of Williamson�s worknbsp;that there is now almost complete accord among palaeo-botanical writers as to the affinities of Calamitean plants.

� The original specimens described by Goppert are in the rich palaeobotanical Collection of the Breslau Museum.

In the following account of the Galamites, the generic name Galamites is used in a wide sense as including stemsnbsp;possessing different types of internal structure; when it isnbsp;possible to recognise any of these structural types the termsnbsp;Calamodendron, Arthropitys or Arthrodendron are used asnbsp;subgenera. The reasons for this nomenclature are discussed innbsp;a later part of the Chapter.

( This term was originally applied to the common pith-casts of Cala-mitean stems, without reference tonbsp;1 internal structure.

Subgenera Calamodendron, Brongniart, 1849 'i These name.s Arthropitysnbsp;nbsp;nbsp;nbsp;Goppert,nbsp;nbsp;nbsp;nbsp;1864 I have primarily re-

Arthrodendron nbsp;nbsp;nbsp;Scottnbsp;nbsp;nbsp;nbsp;1897 j ferenoe to internal

No fossils are better known to collectors of Coal-Measure plants than the casts and impressions of the numerous speciesnbsp;of Galamites. In sandstone quarries of Upper Carboniferousnbsp;rocks there are frequently found cylindrical or somewhatnbsp;flattened fossils, varying from one to several inches in diameter,nbsp;marked on the surface by longitudinal 'ridges and grooves,nbsp;and at more or less regular intervals by regular transversenbsp;constrictions. Similar specimens are still more abundant asnbsp;flattened casts in the blocks of shale found on the rubbishnbsp;heaps of collieries. The sandstone casts are often separatednbsp;from the surrounding rock by a loose brown or black crumblingnbsp;material, and the specimens in the shale �are frequently coverednbsp;by a thin layer of coal.

Most of the earlier writers regarded such specimens as the impressions of the ribbed stems of plants similar to or identicalnbsp;with reeds or grasses. Suckow, and afterwards Dawes and others,nbsp;expressed the opinion that the ordinary Calamite cast represented a hardened mass of sand or marl, which had filled up the

pith of a stem either originally fistuiar or rendered hollow by decay. The investigation of the internal structure confirmednbsp;this view, and proved that the surface-features of a Calamitenbsp;stem do not represent the external markings of the originalnbsp;plant, but the form of the inner face of the cylinder of wood.nbsp;The ribs represent the medullary rays of the original stem ornbsp;branch, and the intervening grooves mark the position of thenbsp;strands of xylem which are arranged in a ring round a largenbsp;hollow pith�.

With this brief preliminary account we may pass to a detailed description of the anatomical characters of Calamites.

Arborescent plants reaching a height of several meters, and having a diameter of proportional size. In habit ofnbsp;growth the Calamites bore a close resemblance to Equisetum;nbsp;an underground rhizome giving off lateral branches and erectnbsp;aerial shoots bearing branches, either in whorls from regularlynbsp;recurring branch-bearing nodes, or two or three from eachnbsp;node; and in some cases the stems bore occasional brarjphesnbsp;from widely separated nodes. The leaves were disposed innbsp;whorls either as star-shaped verticils on slender foliage shoots,nbsp;or in the form of a circle of long narrow leaves on the node of anbsp;thicker branch. Adventitious roots w'ere developed from thenbsp;nodal regions of underground and aerial stems. The cones hadnbsp;the form of long and narrow strobili consisting of a central axisnbsp;bearing whorls of sterile and fertile appendages; the latter innbsp;the form of sporangiophores bearing groups of sporangia. Thenbsp;strobili were heterosporous in some cases, isosporous in others.nbsp;The stems had a large hollow pith bridged across by anbsp;transverse diaphragm at the nodes in the centre of the singlenbsp;stele; the latter consisted of a ring of collateral bundlesnbsp;separated from one another by primary medullary rays. Eachnbsp;group of xylem was composed of spiral, annular, scalariform andnbsp;occasionally reticulate tracheids, the position of the protoxylemnbsp;being marked by a longitudinal carinal cafaal. The shoots andnbsp;roots grew in thickness by means of a regular cambium la3quot;er.nbsp;The cortex consisted of parenchymatous and sclerenchymatous

cells, with scattered secretory sacs. The increase in girth of the central cylinder was often accompanied by a considerablenbsp;development of cortical periderm. The roots differed from thenbsp;shoots in having no carinal canals, and in the possession of anbsp;solid pith and centripetally developed primary xylem groupsnbsp;alternating with strands of phloem.

The above incomplete diagnosis includes only some of the more important structural features of the genus. Thanks tonbsp;the researches begun by the late Mr Binney of Manchester andnbsp;considerably extended by Carruthers, Williamson and laternbsp;investigators, we are now in a position to give a fairly completenbsp;account of Galamites. The type of stem most frequently metnbsp;with in a petrified condition in the English rocks is that tonbsp;which G�ppert applied the name Arthropitys, and it is thisnbsp;subgenus that forms the subject of the following description.nbsp;Our knowledge of Calamitean anatomy is based on the examination of numerous fragments of petrified twigs and othernbsp;portions of different specific types of the genus. It is seldomnbsp;possible to differentiate specifically between the isolatednbsp;fragments of stems and branches which are met with in calcareous or siliceous nodules. As so frequently happens in fossil-plant material, large specimens showing good surface featuresnbsp;and broken fragments with well-preserved internal structurenbsp;have to be dealt with separately.

A transverse section of a young twig, such as is represented in fig. 71, illustrates the chief characteristics of the primarynbsp;structure of a young branch of Galamites. The figure has beennbsp;drawn from a section originally described by Hick^ in 1894.nbsp;A very young Calamite twig bears an exceedingly close resemblance to the stem of a recent Equisetum. The axial regionnbsp;of the stem may be occupied by parenchymatous cells, or thenbsp;absence of cells in the centre may indicate the beginning of thenbsp;gradual formation of the hollow pith, which is one of thenbsp;characteristics of Galamites. The student of petrified Palaeozoic

plants must constantly be on his guard against the possible misinterpretation of Stigmarian � rootlets,� which are frequentlynbsp;found in intimate association with fossil tissues. The intrusionnbsp;of these rootlets is admirably illustrated by a section of a Cala-mite stem in the Williamson Collection (No. 1558) in which thenbsp;hollow pith, 2 cm. broad, contains more than a dozen Stigmariannbsp;appendages.

In the figured specimen of a Calamite twig (fig. 7l) there is a clearly marked differentiation into a cortical regionnbsp;and a large stele or central cylinder. The pith-cells are alreadynbsp;partially disorganised, but there still remain a few fairly largenbsp;parenchymatous cells internal to the ring of vascular bundles.nbsp;The few irregular projections into the cavjty of the large pithnbsp;consist of small fragments of cells, which may be the resultnbsp;of fungal action. Mycelia of fungi are occasionally met with innbsp;the tissues of older Calamite stems.

The position of the primary xylem groups is shown by the conspicuous and regularly placed canals, c; these have beennbsp;s.nbsp;nbsp;nbsp;nbsp;20

formed in precisely the same manner as the corresponding spaces in an Equisetum stem, and they are spoken of in bothnbsp;genera as the carinal canals. Each canal owes its origin to thenbsp;disorganization and tearing apart of the protoxylem elementsnbsp;and the surrounding cells. This may be occasional!}^ seen innbsp;examples of very young Calamites; the canals of a young twignbsp;often contain apparently isolated rings which are coils ofnbsp;elongated spiral threads. Fig. 72, 5 represents the canal of anbsp;twig, cut in an oblique direction, in which the remains of spiralnbsp;tracheids are distinctly seen. In the stem of fig. 7l thenbsp;development has not advanced far enough to enable us tonbsp;clearly define the exact limits of each xylem strand. Thenbsp;smaller elements bordering the canals constitute the primarynbsp;xylem, they are fairly distinct on the outer margin of somenbsp;of the canals seen in the section. Between the small patchesnbsp;of primary xylem the outward extensions of the parenchymanbsp;of the pith constitute the primary medidlary rays, mr. Thenbsp;distinct line encircling the canals and primary xylem has beennbsp;described by Hick as marking the position of the endodermis,nbsp;but it may possibly owe its existence to the tearing of the tissuesnbsp;along the line where cambial activity is just beginning. Thisnbsp;layer of delicate dividing cells would constitute a naturalnbsp;line of weakness. External to this line we have a zone ofnbsp;tissue a, d, containing here and there larger cells with blacknbsp;contents, which are no doubt secretory sacs. It is impossible tonbsp;distinguish with certainty any definite phloem groups, but innbsp;other specimens these have been recognised immediately external to each primary xylem gi�oup ; the bundles were typicallynbsp;collateral in structure. Towards the periphery of the twig thenbsp;preservation is much less perfect; the outer portion of thenbsp;inner cortex, d, consists of rather smaller and thicker-wallednbsp;cells, but this is succeeded by an ill-defined zone containing anbsp;few scattered cells, b, which have been more perfectly preserved.nbsp;The twig is too young to show any secondary tissue in the cortex;nbsp;but the tangential walls in some of the cortical cells afford evidencenbsp;of meristematic activity, which probably represents the beginningnbsp;of cork-formation. The limiting line, e, possibly represents thenbsp;cuticularised outer walls of an epidermal layer. The irregularly

wavy character of the surface of the specimen is probably the result of shrinking, and does not indicate original surface features.

In examining sections of calcareous nodules from the coal seams one meets with numerous fragments of small Calamiteannbsp;twigs with little or no secondary wood; in some of these therenbsp;is a small number of carinal canals, in others the canals arenbsp;much more abundant. The former probably represent thenbsp;smaller ramifications of a plant, and the latter may he regardednbsp;as the young stages of branches capable of developing intonbsp;stout woody shootsh Longitudinal sections of small branchesnbsp;teach us that the xylem elements next the carinal canals arenbsp;either spiral or reticulate in character, the older tracheids beingnbsp;for the most part of the scalariform type, with bordered pits onnbsp;the radial walls. This and other histological characters arenbsp;admirably shown in the illustrations accompanying Williamsonnbsp;and Scott�s memoir on Galamites. The student should treatnbsp;the account of the anatomy of Galamites given in these pagesnbsp;as introductory to the much more complete description bynbsp;these authors. They thus describe the course of the vascularnbsp;bundles in a Calamitean branch ;�

�The bundle-system of Galamites bears a general resemblance to that of Equisetum. A single leaf-trace enters the stem from each leaf, and passes vertically downwards to thenbsp;next node. In the simplest cases the bundle here forks, its twonbsp;branches attaching themselves to the alternating bundles whichnbsp;enter the stem at this node. In other cases both the forksnbsp;attach themselves to the same bundle, so that, in this case,nbsp;there is no regular alternation. In other cases, again, thenbsp;bundle runs past one node without forking, and ultimatelynbsp;forms a j unction with the traces of the second node below itsnbsp;starting-point. These variations may all occur in the samenbsp;specimen. The xylem at the node usually forms a continuousnbsp;ring, for where the regular dichotomous forks of the bundlesnbsp;are absent their place is usually taken by anastomoses^�

As in Equisetum, the xylem at the nodes possesses certain �characteristic features which distinguish it from the internodal

^ On this point vwl,e Williamson and Scott (94), p. 869. ^ Williamson and Scott, loc. cit. p. 876.

strands. It has already been pointed out that the xylem of Equisetum increases in breadth at the nodes (p. 251, fig. 55, 4):

		M
s	i
	(1
'3 j	IVA
	1
sa	{		~
If

	1		1

� p

Fig. 72. A. External xylem elements and cambium, c, with imperfect phloem. X100.

Badial longitudinal section through nodal xylem, px. x 35. Phloem elements; s, sieve-tubes; p, p, parenchymatous cells.

-C. After Williamson and Scott. D. After Eenault.) the same is true of Calamites. In fig. 72, C, we have part ofnbsp;a radial section of a Calamite twig in which the broad massnbsp;of short nodal tracheids is clearly shown; this nodal woodnbsp;forms a prominent projection towards the pith. In the lowernbsp;part of the section the remains of some spiral protoxylemnbsp;tracheids are seen in a carinal canal.

The tracheids of the nodal wood are often reticularly pitted, and so differ in appearance from the ordinary scalariformnbsp;elements.

It is rare to find the phloem clearly preserved, but in specimens where it has been possible to examine this portion ofnbsp;the vascular bundles, it is found to consist of elongated

cambiform cells and sieve-tubes. An unusually perfect specimen has been described by Renault' in which the phloem elements are preserved in silica. Fig. 72, D, is copiednbsp;from one of Renault�s drawings, the sieve-tubes, s, s, shownbsp;several distinct sieve-plates on the lateral walls of the tubes,nbsp;reminding one to some extent of the sieve-tubes in a Brackennbsp;Fern. The cells, p, p, associated with the sieve-tubes arenbsp;square-ended elongated parenchymatous elements. Anothernbsp;characteristic feature illustrated by longitudinal sections isnbsp;the nodal diaphragm; except in the smallest branches thenbsp;interior of each internode is hollow, and the ring of vascularnbsp;bundles is separated from the pith-cavity by a band of parenchymatous tissue. At each node this parenchyma extendsnbsp;across the central cavity in the form of a nodal diaphragm, asnbsp;in the stem of Equisetum.

By far the greater number of the petrified fragments of Calamites afford proof of cambial activity, and possess obviousnbsp;secondary tissues. In exceptionally perfect specimens thenbsp;xylem tracheids are found to be succeeded externally by a fewnbsp;flattened thin-walled cells which are in a meristematic condition (fig. 72, A, c); these constitute the cambium zone, andnbsp;it is the secondary structure that results from the activity ofnbsp;the meristematic cells that we have now to consider.

In petrified examples of branches in which the secondary thickening has reached a fairly advanced stage, the wood isnbsp;usually the outermost tissue preserved, the more externalnbsp;tissues having been detached along the line of cambium cells.nbsp;It is only in a few cases that we are able to examine all thenbsp;tissues of older examples.

The specimen represented in fig. 73 illustrates very clearly the extension of the hollow pith up to the inner surface ofnbsp;the vascular ring; the disorganisation of the pith-cells whichnbsp;had already begun in the twig of fig. 71 has here advancednbsp;much further. The bluntly rounded projections represent thenbsp;prominent primary xylem strands, each of which is traversednbsp;by the characteristic carinal canal. Alternating with thenbsp;wedge-shaped groups of secondary xylem, x, we have the broadnbsp;' Renault (93), PI. xlvii. fig. 4.

principal medullary rays, mr, which become slightly narrower towards the outside. The inner face of each of these wide rays

has a concave form, due to the less resistent nature of the medullary-ray cells as compared with the stronger xylem.nbsp;The regularly sinuous form of the inner face of the vascularnbsp;cylinder enables one to realise how the Calamite-casts (figs. 82,nbsp;99, and 101) have come to have the regular ridges and grooves onnbsp;their surface. The broad ridges on the cast mark the positionnbsp;of the wide medullary rays, while the grooves correspond tonbsp;the more prominent ends of the vascular strands. The tissuesnbsp;external to the wood have not been preserved .in the examplenbsp;shown in fig. 73. Some silicified specimens described bynbsp;Stur* from Bohemia and now in the Museum of the Austriannbsp;Geological Survey, Vienna, admirably illustrate the connectionnbsp;between the surface features of a Calamite cast and the anatomynbsp;of the stem.

In the large section of a calcareous nodule diagrammatically shown in fig. 17 ii. (p. 85) the secondary wood of a slightly'nbsp;flattened Calamite is the most prominent plant fragment.nbsp;The pith-cavity has been almost obliterated by the lateral compression of the woody cylinder, but the presence of the carinal

canals along the inner edge of the wood may still be readily recognised. The appearance presented by a transverse sectionnbsp;of the secondary wood of a Calamite is that of regularnbsp;radial series of rather small rectangular tracheids, with occasional secondary medullary rays consisting of narrow andnbsp;radially elongated parenchymatous cells. The principal rays'nbsp;in the Arthropitys type of a Calamite stem are often found tonbsp;gradually decrease in breadth as they pass into the secondarynbsp;wood, until in the outer portion of the wood the primarynbsp;medullary rays are practically obliterated by the formationnbsp;of interfascicular xylem.

In fig. 74, J., we have a portion of a single xylem group of a thick woody stem. The stem from which the figure hasnbsp;been drawn was originally described by Binney'' as Calamo-dendron commune; we now recognise it as a typical example ofnbsp;the subgenus Arthropitys. The specific term communis wasnbsp;used by Ettingshausen� in 1855 in a comprehensive sense tonbsp;include more than twenty species of the genus Catamites, butnbsp;since Binney�s use of the term it has come to be associatednbsp;with a definite type of Arthropitys stem, in which the primarj'nbsp;medullary rays decrease rapidly in breadth towards the periphery of the wood. The wood of Binney�s stem* measures 2'5 cm.nbsp;across, but the pith-cavity has been crushed to the limits of anbsp;narrow band represented in the figure by the shaded portion.nbsp;The strand of cells, s, in the pith is a portion of a Stigmariannbsp;appendage (� rootlet �), which penetrated into the hollow stemnbsp;of the Calamite and became petrified by the same agency tonbsp;which the preservation of the stem is due. These intrudednbsp;Stigmarian appendages are of constant occurrence in the calcareous nodules; their intimate association with the tissues ofnbsp;other plants is often a serious source of en-or in the identification of petrified tissues. The inner portion of one of the

1 The terra primary ray may be conveniently restricted to the truly primary interfascicular tissue, and the term principal ray may be used for the outwardnbsp;extension of the primary rays by the cambium [Williamson and Scott (94),nbsp;p. 8781.

^ The sections of fossil plants described by Binney were presented to the Woodwardian Museum, Cambridge, by his son (Mr J. Binney).

xylem groups is shown in fig. 74, J.. External to the carinal canal, the xylem tracheids are disposed in regular series and

{Arthropitys) communis (Binney).] s, Stigmariau appendage, x, xylem. From a specimen in thenbsp;Binney Collection, Cambridge, x 50.

h, hypodermal tissue; c, inner cortex. From a specimen in the Williamson Collection {no. 62). x 35.

associated with numerous narrow secondary medullary rays. The width of the xylem wedge increases gradually as we passnbsp;outwards, this is due to the formation of interfascicular xylem,nbsp;which in the more peripheral portion of the stem extendsnbsp;across the primary medullary rays. The few primary medullary-ray cells shown in the drawing illustrate the characteristicnbsp;tangentially elongated form and large size of the parenchymatous elements. Williamson and Scott have pointed out thatnbsp;the tangentially elongated form of the medullary-ray cells is the

result of active growth, and not merely the expression of the tangential stretching of the stem consequent on secondarynbsp;thickening.

A glance at the complete transverse section of the stem,� of which a small portion is shown in fig. 74 A,�suggests thenbsp;existence of annual rings in the wood, but this appearance ofnbsp;rings is merely the result of compression. The secondary woodnbsp;of a Calamite does not exhibit any regular zones of growthnbsp;comparable with the annual rings of our forest trees.

Before passing to other examples of Calamitean stems, reference may be made to the sections shown in figs. 7 5 and 76, which illustrate some further points in the structure of Binney�s stems.nbsp;In fig. 75 the xylem tracheids are shown at x, and betweennbsp;them the secondary medullary rays present the appearance of

long and narrow parenchymatous cells ; as the section is tangential the characteristic scalariform character of the tracheids is not shown, the ladder-like bordered pits being confined tonbsp;the radial walls of the tracheal elements. The much greaternbsp;length than breadth of the cells which form the rays associatednbsp;with the xylem tracheids, is a characteristic feature in Calainiteannbsp;stems. The breadth of the principal ray, m, shows that thenbsp;section has passed through the wood a short distance from thenbsp;pith; in a tangential section cut further into the wood thenbsp;breadth of the principal rays would be considerably reduced.nbsp;The large medullary-ray tissue consists of square-wallednbsp;parenchymatous cells. The more highly magnified section, in

fig. 76, shows a central group of parenchyma containing a few transversely cut tracheids, but the two kinds of elementsnbsp;are not clearly differentiated in the figure; this group of cells is

an outgoing leaf-trace which is enclosed by the strongly curved tracheids of the stem. The section is taken from the node ofnbsp;a stem where several leaf-trace bundles are passing out to anbsp;whorl of leaves; the few cells intercalated between the tracheidsnbsp;belong to the parenchyma of the secondary medullary rays.

In the small portion of a stem represented in fig. 74 5, the cortical tissues have been partially preserved; at the inner edge,nbsp;next the hollow pith, there are two xylem groups, each with anbsp;carinal canal, and between them is part of a broad � principal �nbsp;medullary rayh The cambium has not been preserved, butnbsp;beyond this region we have some of the large cells, c, of thenbsp;inner cortex; these are followed by a few remnants of a smaller-celled tissue, and external to tbis part of the cortex there is anbsp;series of triangular groups, h, consisting of small thick-wallednbsp;cells alternating with spaces which were originally occupied bynbsp;more delicate parenchyma. The darker groups constitutenbsp;hypodermal strands of mechanical tissue or stereome whichnbsp;lent support to the stem. The surface of a stem possessingnbsp;such supporting strands would probably assume a longitudinallynbsp;wrinkled or grooved appearance on drying; the interveningnbsp;parenchyma, contracting and yielding more readily, would tendnbsp;to produce shallow grooves alternating with the ridges abovenbsp;the stereome strands.

The complete section of the stem of which a small portion is shown in fig. 74 B, is figured by Williamson^ in his 12thnbsp;memoir on Coal-Measure plants. The section was obtainednbsp;from Ashton-under-Lyne in Lancashire; it illustrates verynbsp;clearly a method of preservation which is occasionally metnbsp;with among petrified plants. The walls of the various tissuenbsp;elements are black in colour and somewhat ragged, and thenbsp;general appearance of the section is similar to that of a sectionnbsp;of a charred piece of stem. It is possible that the Calamitenbsp;twig was reduced to charcoal before petrifaction by a lightningnbsp;flash or some other cause.

It is often said that the surface of a Calamite stem was probably marked by regular ridges and grooves similar to those

of the pith-cast, and that such external features are connected with the arrangement of the tissues in the vascular cylinder.nbsp;The indication of grooves and ridges on the bark of fossil Ca-lamites is no doubt the result of the existence in the hypoderm

N.1.

[Mi

N.3.

Fig. 77. Portion of a Calamite stem, showing the surface of the bark, c; the wood, b; the surface of the pith-oast, a. N.1�N.S. Nodes. E. Root.nbsp;(After Grand�Eury. Partially restored from a specimen in the �oole desnbsp;Mines, Paris.) J nat. size.

of firm strands alternating with strands of less resistant cells. It is very common to find Calamite pith-casts covered withnbsp;a layer of coal presenting a ribbed surface, hut this is simplynbsp;due to the moulding of the coaly film on an internal pith-cast.

The broad grooves on such a specimen as that of fig. 77 are, on the other hand, probably an indication of the existence ofnbsp;hypoderm bands similar to those in fig. 74 il, A. The specimennbsp;from which fig. 77 is drawn shows many interesting features.nbsp;The figure given by Grand�Eury, of which fig. 77 is a copy, isnbsp;somewhat idealised, but the various surfaces can be made outnbsp;in the fossil. The surface of the coaly envelope surroundingnbsp;the pith-cast, a, is distinctly grooved, but the depressions havenbsp;nothing to do with the surface features of the wood or the pith-cast ; they are no doubt due to the occurrence of alternatingnbsp;bands of thick- and thin-walled tissue in the hypodermal regionnbsp;of the cortex; the peripheral strands of bast cells would standnbsp;out as prominent ribs as the stem tissue contracted during fos-silisation. At b (fig. 77) we have a view of the wood in which thenbsp;position of the principal rays is indicated by fine longitudinalnbsp;lines at regular intervals ; the oval projections just below thenbsp;nodal line are probably the casts of infranodal canals (of. p. 324).nbsp;At a the characteristic pith-cast is seen with a small branph-scar on the node. The scar on the middle node, JV 2, is probabtynbsp;that of a root, and a root H is still attached to the node. A� 3.

An interesting feature observed in some specimens of older Calamite.branches is the development of periderm or cork. Thisnbsp;is illustrated on a large scale by a unique specimen originallynbsp;described by Williamson in 1878k Figs. 78 and 79 representnbsp;transverse and longitudinal sections of this stem. This unusually large petrified stem was found in the Coal-Measuresnbsp;of Oldham, in Lancashire. In the slightly reduced drawing,nbsp;fig. 78, the large and somewhat flattened pith, p, 4'2 cm.nbsp;in diameter, is shown towards the bottom of the figure. Surrounding this we have 58 or 59 wedge-shaped projecting xylemnbsp;groups and broad medullary rays; the latter soon becomenbsp;indistinguishable as they are traced radially through the thicknbsp;mass of secondary wood, 5 cm. wide, composed of scalariformnbsp;tracheids and secondary medullary rays (fig. 78, 3). Thenbsp;secondary wood presents the features characteristic of Gala-mites {Arthropitys) communis (Binney). External to the woodnbsp;there is a broken-up mass, about 5'5 cm. wide composed ofnbsp;1 Williamson (78), p. 323, PL xx. figs. 14 and 15.

regularlj' arranged (fig. 78,2) and rather thick-walled cells; this consists of periderm, a secondar}^ tissue, which has been

developed by a cork-cambium during the increase in girth of the plant. The more delicate cortical tissues have not beennbsp;preserved, and the more resistant portion of the bark has beennbsp;broken up into small pieces of corky tissue, among which arenbsp;seen numerous Stigmarian appendages, pieces of sporangia andnbsp;other plant fragments. These associated structures cannot ofnbsp;course be shown in the small-scale drawing of the figure.

In the radial longitudinal section (fig. 79) we see the pith with the projecting wood and the remains of a diaphragm at the

node. The mottled or watered appearance of the wood is due to numerous medullary rays which sweep across the tracheids. The

From a specimen in the Williamson Collection, British Museum (no. 80). f nat. size.

periderm elements, as seen in longitudinal section, are fibrous in form.nbsp;nbsp;nbsp;nbsp;'

The development of cork in a younger Calamite stem is clearly shown in a specimen described by Williamson and Scottnbsp;in their Memoir of 1894. In a transverse section of the stemnbsp;several large cells of the inner cortex are seen to be in processnbsp;of division by tangential walls, and giving rise to radiallynbsp;arranged periderm tissue 1

The section diagrammatically sketched in fig. 80 is that of a Calamite twig in which the wood appears to have been injured,nbsp;and the wound has been almost covered over by the formationnbsp;of callus wood. The young trees in a Palaeozoic forest mightnbsp;easily be injured by some of the large amphibians, which werenbsp;the highest representatives of animal life during the Carboniferous period, just as our forest trees are often barked by deer,nbsp;rabbits, and other animals. Fissures might also be formed bynbsp;the expansion of the bark under the heating influence of thenbsp;sun�s rays^. Such a specimen as that of fig. 80 gives an air ofnbsp;living reality to the petrified fragments of the Coal period trees.

It is well known how a wound on the branch of a forest tree becomes gradually overgrown'by-the activity of the cambiumnbsp;giving rise to a thick callus, which gradually closes over the

wounded surface in the form of two lips of wood which finally meet over the middle of the scar. The two lips of callus arenbsp;clearly shown in the fossil branch arching over the tear in thenbsp;wood just beyond the ring of carinal canals. The tissue externalnbsp;to the wood represents the imperfectly preserved cortex. Anbsp;section which was cut parallel to that of fig. 80 shows a continuous band of wood beyond the wound, and the latter hasnbsp;the form of a small triangular gap; this section appears tonbsp;have passed across the wound where it was narrower and hasnbsp;already been closed over by the callus. The formation of anbsp;rather different kind of callus wood has been described bynbsp;Renault' and by Williamson and Scott^, in stems where abortednbsp;or deciduous branches have been overgrown and sealed upnbsp;by cambial activity.

^ Williamson and Scott, loc. cit. p. 893. Vide specimens 133*�135* in the Williamson Collection.

Some of the features to be noticed in longitudinal sections of Calamite stems have already been described, at least as regards youngernbsp;branches. The specimen shown in fig. 81nbsp;illustrates the general appearance of a stemnbsp;as seen in tangential and radial section. Innbsp;the lower portion, T, the course of the vascular bundles is shown by the black linesnbsp;which represent the xylem tracheids, bifurcating and usually alternating at each node.

Between the xylem strands are the broad principal medullary rays. At 6 a branchnbsp;has been cut through on its passage outnbsp;from the parent stem, just above the nodalnbsp;line. In tangential sections of Calamitenbsp;stems one frequently sees both branchesnbsp;and leaf-trace bundles (fig. 83, A), passingnbsp;horizontally through the wood and enclosednbsp;by strongly curved and twisted tracheids.

In the upper part of the figure (81, iJ), the section has passed through the centre ofnbsp;the stem, and the wood is seen in radialnbsp;view; each node is bridged across by anbsp;diaphragm of parenchymatous cells capablenbsp;of giving rise to a surface layer of peridernd.

An outgoing branch, as seen in a tangential section of a stem, consists of a parenchymatous pith surrounded by a ringnbsp;of vascular bundles, in which the characteristic carinal canals have not yet beennbsp;formed, but if the section has cut the branchnbsp;further from its base, there may be seen a circle of irregularnbsp;gaps marking the position of the carinal canals. Such gapsnbsp;are often occupied by thin parenchyma, and contain protoxylemnbsp;elements. The outgoing branches, as seen in a tangential sectionnbsp;of a Calamite stem, are seen to be connected with the wood ofnbsp;the parent stem by curved aiid sinuous tracheids, which givenbsp;^ E.g. specimen las'*** in the 'Williamson Collection.

to the stem-wood a curiously characteristic appearance^ as if the xylem elements had been pushed aside and contorted bynbsp;the pressure of the outgoing member. A tangential sectionnbsp;through a Pine stem^ in the region of a lateral branch presentsnbsp;precisely the same features as in Calamites. The branches arenbsp;given off from the stem immediately above a node and usuallynbsp;between two outgoing leaf-trace bundles.

Specimens of pith-casts occasionally present the appearance of a curved and rapidly tapered ram�s horn, and the narrownbsp;end of such a cast is sometimes found in contact with the nodenbsp;of another cast. This juxtaposition of casts is shown unusuallynbsp;well in fig. 82. In some of the published restorations of Calamitesnbsp;the plant is represented as having thick branches attached tonbsp;the main stem by little more than a point. Williamson^ clearlynbsp;explained this apparently unusual and indeed physically impossible method of branching, by means of sections of petrified stems.nbsp;The branches seen in fig. 82 are of course pith-casts, and in thenbsp;living plant the pith of each branch was surrounded by a massnbsp;of secondary wood developed from as many primary groupsnbsp;of xylem as there are grooves on the surface of the cast, eachnbsp;of the grooves on an iriternode corresponding to the projectingnbsp;edge of a xylem group. At the junction of one branch withnbsp;another the pith was much narrower and the enclosing woodnbsp;thicker, so that the tapered ends of the cast merely show thenbsp;continuity by a narrow union between the pith-cavities ofnbsp;different branches. Most probably the casts of fig. 82 are thosenbsp;of a branched rhizome which grew underground, giving offnbsp;aerial shoots and adventitious roots. There is a fairly closenbsp;resemblance between the Calamite casts of fig. 82 and a stoutnbsp;branching rhizome of a Bamboo, e.g. Bambusa arundinaceanbsp;Wind.; it is not surprising that the earlier writers looked uponnbsp;the Calamite as a reed-like plant.

* Vide Williamson (71), PI. xxviii. fig. 38; (71�), PI. iv. fig. 15; (78), PI, xxi. figs. 26�28. Williamson and Scott (94), PL lxxii. figs. 5 and 6. Renault (93),nbsp;PI. xLv. figs. 4�6, etc. Felix (96), PI. it. figs. 2 and 3.

is another feature to which attention must be drawn.. On the casts shown in fig. 82 there is a circle of small oval scarsnbsp;situated just below the nodes, these are clearly shown atnbsp;c, c. c. Each of the scars is in reality a slight projectionnbsp;from the upper end of an internodal ridge. As the ridgesnbsp;correspond to the broad inner faces of medullary rays, the

small projection at the upper end of each ridge is a cast of a depression or canal which existed in the medullary tissue ofnbsp;the living plant. There have been various suggestions as tonbsp;the meaning of these oval projections; several writers havenbsp;referred to them as the points of attachments of roots or othernbsp;appendages, hut Williamson proved them to be the castsnbsp;of canal-like gaps which traversed the upper ends of principal medullary rays in a horizontal direction. In a tangentialnbsp;section of a Calamite stem the summit of each primarynbsp;medullary ray often contains a group of smaller elements whichnbsp;are in process of disorganisation, and in some cases thesenbsp;cells give place to an oval and somewhat irregular canal.nbsp;In the diagrammatic tangential section represented in fig. 83, Anbsp;the upper end of each ray is perforated by a large ovalnbsp;space, which has been formed as the result of the breakingnbsp;down of a horizontal band of cells. Williamson designatednbsp;these spaces infranodal canals. While proving that they hadnbsp;nothing to do with the attachment of lateral members,nbsp;he suggested that they might be concerned with secretion;nbsp;but their physiological significance is still a matter of speculation. The casts of infranodal canals are especially large andnbsp;conspicuous in the subgenus Arthrodendron, a form of Calamitenbsp;characterised by certain histological features to be referred tonbsp;later. Williamson^ originally regarded the presence of infranodal canals as one of the distinguishing features of Arthrodendron, but they occur also in the casts of the commonernbsp;type Arthropitys. As a rule we have only the cast of thenbsp;inner ends of the infranodal canals preserved as slight projections like those in fig. 83, A; but in one exceptionally interesting pith-cast described by Williamson, these casts of thenbsp;infranodal canals have been preserved as slender spoke-likenbsp;Icolumns radiating from the upper ends of the ridges of thenbsp;infranodal region of a pith-cast.

This specimen, which was figured by Williamsonquot; in two of his papers, and by LyelP in the fifth edition of his Elementary

Geology, is historically interesting as being one of the first important plants obtained by Williamson early in the fifties,nbsp;when he began his researches into the structure of Carboniferous plants. A joiner, who was employed by Williamsonnbsp;to make a piece of machinery for grinding fossils, brought anbsp;number of sandstone fragments as an offering to his employer,nbsp;whom he found to be interested in stones. The specimensnbsp;� w�ere in the main the merest rubbish, but amongst them,�nbsp;writes Williamson, � I detected a fragment which was equallynbsp;elegant and remarkable... In later days, when the specimen sonbsp;oddly and accidentally obtained, came to be intelligently studied,nbsp;its history became clear enough, and the priceless fragmentnbsp;is now one of the most precious gems in my cabineth�

Oomparison of three types of structure met with in Calamitean stems,�Arthropitys, Arthrodendron, mid Calamodendron.

The anatomical features which have so far been described as chai-acteristic of Catamites represent the common typd� metnbsp;with in the English Coal-Measures. The same type occurs alsonbsp;in France, Germany and elsewhere. It is that form of stemnbsp;known as Arthropitys, a sub-genus of Galamites.

Arthropitys may be briefly diagnosed as follows,�confining our attention to the structure of the stem : A ring of collateralnbsp;bundles surrounds a large hollow pith, each primary xylemnbsp;strand terminates internally in a more or less bluntly roundednbsp;apex traversed by a longitudinally carinal canal. The principalnbsp;medullary rays consist of large-celled parenchyma, of which thenbsp;individual elements are usually tangentially elongated as seennbsp;in transverse section, and four or five times longer than broadnbsp;as seen in a tangential longitudinal section. The secondarynbsp;xylem consists of scalariform and reticulately pitted tracheids ;nbsp;the interfascicular xylem may be formed completely across eachnbsp;primary ray at an early stage in the growth of the stem^, ornbsp;it may be developed more gradually so as to leave a tapering

principal ray of parenchyma between each primary xyleni bundle. In the latter case the principal rays present the characteristicnbsp;appearance shown in figs. 71, 74, A, 75 and 78, a type of stemnbsp;which we may refer to as Calamites {Arthropitys) communis.nbsp;In the former case the stem presents the appearance shown innbsp;fig. 83, D^. A third variety of Arthropitys stem is one whichnbsp;was originally named by G�ppert Arthropitys histriata; in thisnbsp;form the principal rays retain their individuality as bands ofnbsp;parenchyma throughout the whole thickness of the wood^nbsp;Such stems as those of figs. 73 and 74, B, may be youngnbsp;examples of Arthropitys communis or possibly of A. histriata.nbsp;The narrow secondary medullary rays of Arthropitys usuallynbsp;consist of a single row of cells which are three to five timesnbsp;higher than broad, as seen in tangential longitudinal section.nbsp;Infranodal canals occur in some examples of Arthropitys.

In the subgenus Arthrodendron, a type of stem first recognised by Williamson and named by him Galamopitys^,nbsp;the principal medullary rays consist of prosenckymatous cellsnbsp;{i.e. elongated pointed elements) and not parenchyma. Thesenbsp;elongated elements are not pitted like tracheids, and theynbsp;are shorter and broader than the xylem elements. In somenbsp;examples of this subgenus the primary rays are bridged acrossnbsp;at an' early stage by the formation of secondary interfascicularnbsp;xylem, and in others they persist as bands of ray tissue, as innbsp;Arthropitys. Other characteristics of Arthrodendron are thenbsp;abundance of reticulated instead of scalariform tracheids in thenbsp;secondary wood, and the large size of the infranodal canals.

Fig. 83, D represents part of a transverse section of Arthrodendron', in this stem the rays have been occupied by interfascicular xylem at a very early stage of the secondary growth. The section from which fig. 83, B is drawn was described bynbsp;Williamson in 1871; the complete section shows about 80nbsp;carinal canals and primary xylem groups. The prosenchymatous

� The stem of fig. 83 is an example of Arthrodendron, hut the appearance of the secondary xylem agrees with that in some forms of Arthropitys.

^ For figures of this type of stem vide G�ppert (64); Cotta (50), PI. xv. (specimens 13787 in the British Museum Collection); Mougeot (52), PI. v.;nbsp;Stur (87), pp. 27�31; Eenault (93), Pis. XLiv.*'and xlv. etc.

form of the principal medullary rays is seen in fig 83, G, and the reticulate pitting on the radial wall of a tracheid is shown

in fig. 83, �. Fig. 83, A illustrates the large infranodal canals as seen in a tangential section of a stem. The same sectionnbsp;shows also the course of the vascular bundles characteristic ofnbsp;Calamites as of Equisetum, and the position of outgoing leaf-traces is represented by unshaded areas in the black vascularnbsp;strands.

The subgenus Arthrodendron is very rarely met with, and our information as to this type is far from completeh

The third subgenus Calamodendron has not been discovered in English rocks, and our knowledge of this type is derived from

French and German silicified specimens'. There is the same large hollow pith surrounded by a ring of collateral bundlesnbsp;with carinal canals, as in the two preceding subgenera. Thenbsp;tracheids are scalariform and reticulate, and the secondarynbsp;medullary rays consist of rows of parenchymatous cells whichnbsp;are longer than broad, as in Arthropitys and Arthrodendron.

The most characteristic feature of Calamodendron is the occurrence of several rows of radially disposed thick-wallednbsp;prosenchymatous elements (fig. 84, b) on either flank of each

a, a, xylem tracheids, ft, 6, bands of prosenchyma, c, medullary ray. (After Benault.)

wedge-shaped group of xylem. Each principal ray is thus nearly filled up by bands of fibrous cells on the sides of adjacentnbsp;xylem groups, but the centre of each principal ray is occupiednbsp;by a narrow band of parenchyma (fig. 84, c). The relativenbsp;breadth of the xylem and prosenchymatous bands has beennbsp;made use of by Eenault as a specific character in Galamoden-dron stems. Fig. 84 is copied from a drawing recently publishednbsp;by this French author of a new species of Calamodendron,nbsp;0. intermedium�s. In this case the bands of fibrous cells, h,nbsp;are slightly broader, as seen in a transverse section of the

s- Vide Williamson (87-). In this paper Williamson compares the three subgenera of Calamite stems. Eenault and Zeiller (88), PI. lxxv. Eenaultnbsp;(93), Pis. LViii. and nix.nbsp;nbsp;nbsp;nbsp;'

stem, than the bands of xylem tracheids, a. The narrow band, c, consists of four rows of the parenchymatous tissue of a medullary ray. At the inner end of each group of tracheids there isnbsp;a large carinal canal.

The question of the recognition of the pith-casts of stems possessing the structure of any of the three subgenera ofnbsp;Calamites is referred to in a later section of this chapter.

Leaves of Calamites and Calamitean foliage-shoots, including an account of (a) Calamocladus (Asterophyllites) andnbsp;(/3) Annularia.

Our knowledge of the structure and manner of occurrence of Calamite leaves is very incomplete. There are numerousnbsp;foliage-shoots among the fossils of the Coal-Measures which arenbsp;no doubt Calamitean, but as they are nearly always found apartnbsp;from the main branches and stems, it is generally impossiblenbsp;to do more than speak of them as probably the leaf-bearingnbsp;branches of a Calamite. The familiar fossils known as Astero-phyllites, and in recent years often referred to the genusnbsp;Calamocladus, are no doubt Calamitean shoots; but they arenbsp;usually found as isolated fragments, and it is seldom that wenbsp;are able to refer them to definite forms of Calamites. Anothernbsp;common Coal-Measure genus, Annularia, is also Calamitean,nbsp;and at least some of the species are no doubt leafy shoots ofnbsp;Calamites. Although it is generally accepted that the fossilsnbsp;referred to as Asterophyllites or Calamocladus are portions ofnbsp;Calamites, and not distinct plants, it is convenient, and indeednbsp;necessary, to retain such a term as Calamocladus as a means ofnbsp;recording foliage-shoots, which may possess both a botanical andnbsp;a geological value.

Some of the Calamite casts, especially those referred to the subgenus Calamitina, are occasionally found with leavesnbsp;attached to the nodes. In some stems the leaves are arrangednbsp;in a close verticil, and each leaf has a narrow' linear form andnbsp;is traversed by a single median vein. Figures of Calamite

stems with verticils of long and narrow leaves may be found in Lindley and Hutton', and in the writings of many othernbsp;authors^. In the specimen shown in fig. 85 the leaves arenbsp;preserved apart from the stem, but from their close associationnbsp;with a Calamite cast, and from the proofs afforded by othernbsp;specimens, it is quite certain they formed part of a whorl ofnbsp;leaves attached to the node of a true Calamite, and a stem

having that particular type known as Galamitina^ (dgs. 99,100). It is probable that in some Calarnites, and especially in youngernbsp;shoots, the leaves had the form of narrow sheaths split up intonbsp;linear segments. This question has already been referred to innbsp;dealing with certain Palaeozoic fossils referred to Equisetites^.

A few years ago the late Thomas Hick�, of Manchester, described the structure of some leaves which he believed to benbsp;those of a Calamite. He found them attached to a slendernbsp;axis which possessed the characteristics of a young Calamitenbsp;branch. There can be little doubt that his specimens are truenbsp;Calamite leaves. The sketches of fig. 86 have been made fromnbsp;the sections originally described by Hick. Fig. 86, 1 shows anbsp;leaf in transverse section; on the outside there is a well-defined

1 nbsp;nbsp;nbsp;Lindley and Hutton (31), Pis. cxiv., exc. etc. Most of the specimensnbsp;figured by these authors are in the Newcastle Natural History Museum. Fornbsp;notes on the type-specimens of Lindley and Hutton, vide Howse (88) andnbsp;Kidston (902).

2 nbsp;nbsp;nbsp;Weiss (88), Stur (87), etc.nbsp;nbsp;nbsp;nbsp;� Vide, p. 367.

epidermal layer with a limiting cuticle. Internal to this we have radially elongated parenchymatous cells forming a loose ornbsp;spongy tissue, the cells being often separated by fairly large spaces

1. nbsp;nbsp;nbsp;Transverse section; f, vascular bundle; a, sheath of cells, x 35.

3. nbsp;nbsp;nbsp;A tracheid and a few parenchymatous cells, the latter with nuclei.

(fig. 86, 5), especially in the region of the blunt lateral wings of the leaf Some of these cells contain a single dark dot, whichnbsp;in all probability is the mineralised nucleus. These pallisade-like cells probably contained chlorophyll and constituted thenbsp;assimilating tissue of the leaf. In the centre there is a circularnbsp;strand of cells limited by a layer of larger cells with blacknbsp;contents, enclosing an inner group of small-celled parenchymanbsp;and traversed by a few spiral or scalariform tracheids constitutingnbsp;the single median vein. It is hardly possible to recognise anynbsp;phloem elements in the small vascular bundle ; there appear tonbsp;be a few narrow tracheids surrounded by larger parenchymatous

elements (fig. 86, 2). At one point in the epidermis of fig. 86, 1, there appears to be a stoina, but the details arenbsp;not very clearly shown (fig. 86, 4); the two cells, s, s, borderingnbsp;the small aperture are probably guard-cells.

The nature of the assimilating tissue, the comparatively thick band of thin-walled cells with intercellular spaces, andnbsp;the exposed position of the stomata suggest that the plantnbsp;lived in a fairly damp climate; at least there is nothing tonbsp;indicate any adaptation to a dry climate.

In the Binney collection of plants in the Woodwardian Museum, Cambridge, there is a species of a very small shootnbsp;bearing three or four verticils of leaves which possess the samenbsp;structure as those of fig. 86. We may probably regard suchnbsp;twigs as the slender terminal branches of Calamitean shoots.

The generic name Asterophyllites was proposed by Brongniart^ in 1822 for a fossil previously named by Schlotheim^nbsp;Gasuarinites, and afterwards transferred to Sternberg�s genusnbsp;Annularia. In 1828 Brongniart� gave the following diagnosisnbsp;of the fossils which he included under the genus Aatero-phyllites:�� Stems rarely simple, usually branched, with oppositenbsp;branches, which are always disposed in the same plane; leavesnbsp;flat, more or less linear, pointed, traversed by a simple mediannbsp;vein, free to the base.� Bindley and Hutton described examplesnbsp;of Brongniart�s genus as species of Hippurites*, and othernbsp;authors adopted different names for specimens afterwards referred to Asterophyllites.

At a later date Ettingshausen� and other writers expressed the view that the fossils which Brongniart regarded as a distinctnbsp;genus were the foliage-shoots of Catamites, and Ettingshausennbsp;went so far as to include them in that genus. In view of thenbsp;generally expressed opinion as to the Calamitean nature ofnbsp;Asterophyllites, Schimper� proposed the convenient generic

name Calamocladus for �rami et ramuli foliosi� of Calamites. Some recent authors have adopted this genus, but others prefernbsp;to retain Asterophyllites. In a recent important monograph bynbsp;Grand�Euryi Calamitean foliage-shoots are included under thenbsp;two names, Asterophyllites and Calamocladus; the latter typenbsp;of foliage-shoots he associates with the stems of the subgenusnbsp;Calamodendron, and the former he connects with those Calamitean stems which belong to the subgenus Arthropitys.

It is an almost hopeless task to attempt to connect the various forms of foliage-shoots with their respective stems, andnbsp;to determine what particular anatomical features characterisednbsp;the plants bearing these various forms of shoots. We maynbsp;adopt Schimpers generic name Calamocladus in the samenbsp;sense as Asterophyllites, but as including such other foliage-shoots as we have reason to believe belonged to Calamites.nbsp;Those leaf-bearing branches which conform to the type knownnbsp;as Annularia are however not included in Calamocladus, as wenbsp;cannot definitely assert that these foliage-shoots belong in allnbsp;cases to Calamitean stems. Grand�Eury�s use of Calamockidusnbsp;in a more restricted sense is inadvisable as leading to confusion,nbsp;seeing that this name was originally defined in a more comprehensive manner as including Calamitean leaf-bearing branchesnbsp;generally. We may define Calamocladus as follows:�

Branched or simple articulated branches bearing whorls of uni-nerved linear leaves at the nodes; the leaves may be eithernbsp;free to the base or fused basally into a cup-like sheath {e.g.nbsp;Grand�Eury�s Calamocladus). The several acicular linear leavesnbsp;or segments which are given off from the nodes spread outnbsp;radially in an open manner in all directions; they may benbsp;either almost at right angles to the axis or inclined at differentnbsp;angles. Each segment is traversed by a single vein and terminates in an acuminate apex.

As a typical example of a Calamitean foliage-shoot the species Calamocladus eqiiisetiformis (Schloth.) may be biieflynbsp;described. The synonymy of the commoner species of fossilnbsp;plants is a constant source of confusion and difficulty; in ordernbsp;to illustrate the necessity of careful comparison of specimens

and published illustrations, it may be helpful to quote a few synonyms of the species more particularly dealt with. Thenbsp;exhaustive lists drawn up by Kidston in his Catalogue ofnbsp;Palaeozoic plants in the British Museum will he foundnbsp;extremely useful by those concerned with a systematic studynbsp;of the older plants.

The above synonyms do not exhaust the list�, but they suffice to illustrate the necessity of a careful comparison in drawingnbsp;up tables of species, in connection with geographical distributionnbsp;or for other purposes.

Calamocladus equisetiformis may be briefly defined as follows:�A central axis possessing a hollow pith of Calamiteannbsp;character, divided externally into well-marked slightly constricted nodes and internodes; from the nodes long narrownbsp;and free leaves are borne in whorls; from the axils of some ofnbsp;the leaves lateral branches are given off inclined at a fairlynbsp;wide angle to the main axis, and bearing crowded verticils ofnbsp;spreading acicular leaves.

The unusually good specimen, 38�5 cm. long, shown on a much reduced scale in fig. 87, illustrates the characteristic habitnbsp;of this form of Calamocladus. It is from the Eadstock coal-fieldnbsp;of Somersetshire, one of the best English localities for Coal-Measure plants. An exceedingly good collection of Eadstocknbsp;plants has recently been presented to the British Museum bynbsp;Mr J. McMurtrie ; it includes many fine specimens of Calamites.nbsp;A small example�probably of this species�from Coalbrooknbsp;Dale, near Dudley, in Shropshire, and now in the Britishnbsp;Museum, illustrates very well the appearance of a young and

1 Martin (09), PI. xx. figs. 4 and 6. nbsp;nbsp;nbsp;� Schlotheim (20), p. 397.

� Bindley and Hutton (31), PI. cxoi. nbsp;nbsp;nbsp;� Ettingshausen (55), p. 28.

� For other lists and synonyms, vide Zeiller (88), p. 368, and Kidstou (86), p. 38 and (93), p. 316, also Potoni� (93), p. 162.

partially expanded Calamitean foliage-shoot. The central axis, 6'5 cm. in length, includes about 15 internodes, and terminatesnbsp;in a bud covered by several small leaves. Lateral branches arenbsp;given off at a wide angle, and small unexpanded buds occur innbsp;the axils of several of the leaves.

As an example of the leaf-bearing branches which Grand�-Eury has recently described as Galamocladus, using the genus in a more restricted sense than is adopted in the presentnbsp;chapter, reference may be made to the fragment shown innbsp;fig. 68, A. The foliage-shoots of this type bore verticils of linearnbsp;leaves, coherent basally in the form of a cup, at the ends ofnbsp;branches and not in a succession of whorls on each branch.nbsp;The association of reproductive organs, in the form of longnbsp;and narrow strobili, with Calamocladus is referi'ed to in thenbsp;sequel.

The specimens described by Grand�Eury are in the Ecole des Mines Museum, Paris; some of the shoots which are wellnbsp;preserved bear a resemblance in habit of growth to the genusnbsp;Archaeocalamites.

In 1820 this generic name was applied by Sternberg' to some specimens of branches bearing verticils of linear leaves.nbsp;In 1828 Brongniart^ thus defined the genus Annularia:�.nbsp;�Slender stem, articulated, with opposite branches arisingnbsp;above the leaves. Leaves verticillate, flat, frequently obtuse,nbsp;traversed by a single vein, fused basally and of unequalnbsp;length.�

In the works of earlier writers we find frequent illustrations of specimens of Annidaria, which are compared with Asters andnbsp;other recent flowering plants. Lehmann� contributed a papernbsp;to the Royal Academy of Berlin in 1756, in which he referrednbsp;to certain fossil plants as probable examples of flow^ers, amongnbsp;them being a specimen of Annularia. He refers to the occurrence of fossil ferns and other plants, and asks why we do

not find flowers of the rose or tulip; his object being �not to acquire vain glory, but to give occasion for others to look intonbsp;the matter more clearly.�

The general habit of the fossils which are now included under Annularia agrees closely with that of Galamocladus.nbsp;There is the same spreading form and a similar foliage in thenbsp;two genera, but in Annularia the members of a whorl arenbsp;always fused into a basal sheath, and the segments are notnbsp;of equal length. We may thus summarise the characteristicnbsp;features of the genus:�

Opposite branches are given off in one plane from the nodes of a main axis; the leaves are in the form of narrow sheathsnbsp;divided into numerous and unequal linear or narrow lanceolate segments, each with a median vein. The segments in eachnbsp;whorl appear to be spread out in one plane very oblique to thenbsp;axis of a branch, instead of spreading radially in all directions;nbsp;the lateral segments are usually longer than the upper andnbsp;lower members of a whorl. The vegetative branches possessnbsp;the same type of structure as Galamites.

A comparison of Annularia and Phyllotheca has already been made in Chapter IX. (p. 282). Potoni�^ has recently givennbsp;a detailed account of Annularian leaves; he compares themnbsp;with those of Equisetum, and describes the occurrence on thenbsp;lamina of each leaf-segment of a broad central band or midrib,nbsp;with a groove, probably containing stomata, on either side. Henbsp;shows that in well-preserved specimens of Annularia, it isnbsp;possible to recognise certain minute surface-features, such asnbsp;the presence of hairs and stomata, which enable one to detect anbsp;close resemblance between the leaves of Calamite stems andnbsp;those of Annularian shoots.

It is not always easy to distinguish between Annularia and Galamocladus; the collar-like basal sheath in the leaves of thenbsp;former is a characteristic feature, but that cannot always benbsp;recognised. On the other hand, the leaves of Galamocladusnbsp;may sometimes be flattened out on the surface of the rock andnbsp;simulate the deeply cut sheaths of Annularia. It is difficultnbsp;to decide how far the manner of occurrence of Annularian

leaves in one plane, which is commonly insisted on as a generic character, is an original feature, or how far it is the resultnbsp;of compression in fossilisation. Probably the leaves of a livingnbsp;Annularia were spread out at right angles to the axis, as innbsp;the �verticils� of such a plant as Galium.

Dawson^ has described some fossils from the Devonian rocks of Canada as species of Asterophyllites; the figures bear a closernbsp;resemblance to the genus Annularia. The same author figuresnbsp;some irregularly whorled impressions as Protannularia, whichnbsp;appear to be identical with a fossil described by Nicholson'^ fromnbsp;the Skiddaw slates (Ordovician) of Cumberland as Buthotrephisnbsp;radiata, but the specimens are too imperfect to, admit ofnbsp;accurate determination.

This species was figured by Scheuchzer� in his Herbarium Diluvianum, and compared by him with a species of Galiumnbsp;(Bedstraw). Brongniart first made use of the generic namenbsp;Annularia for this common Coal-Measure species, which maynbsp;be defined as follows:�

Stem reaching a diameter of about 6�8 cm,, with internodes 6�12 cm. in length, the surface either smooth or faintly ribbed.nbsp;Primary branches given off in opposite pairs from the nodes, thenbsp;lateral branches giving off smaller branches disposed in the samenbsp;manner. The smaller branches bear verticils of leaves at eachnbsp;node; both leaves and ultimate branches being in one plane.nbsp;The leaves are narrow, lanceolate-spathulate in form, broadest

2 nbsp;nbsp;nbsp;Nicholson (69) PI. xviii. B. Nicholson�s specimens are in the Wood-

� Bindley and Hutton (31), PI. cxxiv. nbsp;nbsp;nbsp;^ Binney (68), PI. vi. fig. 3.

about the middle, 1�5 cm. in length and 1�^^3 mm. broad, hairy on the upper surface^; each leaf is traversed by a single vein.

Each whorl contains 16�32 segments, which are connected basally into a collar or narrow sheath ; the lateral segments arenbsp;usually longer than the upper and lower. The branches arenbsp;about 6�20 mm. broad, with finel}quot; ribbed intemodes 3�7 cm.nbsp;long, bearing verticils of leaves; the ultimate branches arise innbsp;pairs in the axils of the lateral segments of the verticils.

The strobili are of the Galamostachys'^ type and are borne on the main branches or possibly on the stem ; they have a longnbsp;and narrow form and are attached in verticils at the nodes.nbsp;Each strobilus consists of a central axis bearing alternate whorlsnbsp;of linear lanceolate sterile bracts and sporangiophores, aboutnbsp;half as- numerous as the sterile bracts; each sporangiophorenbsp;bears four ovoid sporangia.

The anatomical structure of a specimen referred to An-nnla7-ia stellata has been described by Renault�. The cortex

consists of parenchyma traversed by lacunae and limited peripherally by a denser hypodermal tissue. In the stelenbsp;Renault describes 14 xylem strands, each with a large carinalnbsp;canal. The pith was apparently large and hollow. The samenbsp;author describes an Annidaria strobilus in which the lowernbsp;sporangiophores bear macrosporangia, and the upper microsporangia.

A. Strobilus (Stacliannularia calathifera, Weiss), f nat. size. B. Vegetative shoot, f nat. size.

From specimens in the Collection of Mr E. Kidstou. Upper Coal-Measures, Badstock.

The references in the footnote should be consulted for figures of this species of Annularia; it is from the examinationnbsp;of such specimens as are referred to in the note that the abovenbsp;diagnosis has been compiledb

^ One of the finest specimens of Annularia stellata is figured by Stur (87), PI. XVI b; it is in the Leipzig Museum. Vide also Schenk (83), PI. xxxix.;nbsp;Germar (44), PL ix.; Renault and Zeiller (88), Pis. xlv. and xlvi. There arenbsp;some well-preserved impressions of A. stellata in the British Museum fromnbsp;Radstock, Newcastle and elsewhere.

Principal branches 8�12 mm. wide, with internodes 8�10 cm. in length, giving off two opposite branches at the nodes;nbsp;from the secondary branches arise smaller branches in oppositenbsp;pairs. The leaf-verticils and branches are all in one plane.nbsp;Each verticil consists of 12�18 spathulate segments, 3�10 mm.nbsp;long, cuneiform at the base andquot; broader above, with an acuminatenbsp;tip; the lateral segments are slightly longer than the uppernbsp;and lower members of a whorl.

The small and crowded leaf-whorls give to this species a characteristic appearance, which readily distinguishes it fromnbsp;the larger-leaved forms such as Ayinularia stellata. A fossilnbsp;figured by Lhwyd^ in 1699 as Rubeola mineralis is no doubt annbsp;example of Annularia sphenophylloides.

Annularian branches are occasionally found with cones given off from the axils of some of the leaf-whorls. An interestingnbsp;specimen, which is now in the Leipzig Museum, was describednbsp;by Sterzel in 1882�, showing cones attached to a vegetativenbsp;shoot of Annularia sphenophylloides. The long and narrownbsp;.strobili��2�5 cm. long and about 6 mm. broad�appear verynbsp;large in proportion to the size of the vegetative branches. Anbsp;fertile shoot consists of a central axis bearing whorls of bractsnbsp;alternating with sporangiophores, to each of which are attachednbsp;four sporangia. The specimen in fig. 89, A, does not show thenbsp;details clearly; each transverse constriction represents thenbsp;attachment of a whorl of linear bracts; the whole cone appearsnbsp;to consist of a series of short broad segments. The divisionsnbsp;in the lower half of each segment mark the position of thenbsp;sterile bracts, while those of the upper half represent the out-

* Weiss (76), p. 27, PI. iii. fig. 2. nbsp;nbsp;nbsp;� Lhwyd (1699), PI. v. fig. 202.

lines of the upper sporangia of each whorl of sporangiophores, the lower sporangia being hidden bj the ring of linear bracts hnbsp;On some portions of the specimen of fig. 89, .4, it is possible tonbsp;recognise the outlines of cells on the coaly surface-film; thesenbsp;probably belong to the sporangium wall. This type of cone isnbsp;included under the genus Oalamostachys, a name applied tonbsp;Calamitean strobili with certain morphological characters, asnbsp;described on p. 851.

In 1871 Williamson^ described some sections of what he considered to be a distinct variety of a Calamite stem. Thenbsp;chief peculiarity which he noticed lay in the absence ofnbsp;carinal canals, and in the solid pith. Some years later thenbsp;same observer� came to the conclusion that the specimens werenbsp;probably those of a plant generically distinct from Galamites;nbsp;he accordingly proposed a new name Astromyelon. Subsequently Cash and Hick^ gave an account of some examples ofnbsp;apparently another form of plant, to which they gave the namenbsp;Myriophylloides Williamsoiiis; and Williamson^ suggested thenbsp;term Helophyton as a more suitable generic designation. Itnbsp;was, however, demonstrated by Spencer� that the plant described by Cash and Hick was identical with Williamson�snbsp;Astromyelon. Williamson�� then gave an account of severalnbsp;�specimens of this type illustrating various stages in the growthnbsp;and development of the Astromyelon �stems,� which he compared with the rhizome of the recent genus Marsilia.

In 1885 Kenault� published an account of Astromyelon in which he brought forward good evidence in favour of regarding itnbsp;as a Calamitean root. The same author has recently given somenbsp;excellent figures and a detailed description of certain specificnbsp;types of these Calamite roots, and Williamson and Scott�snbsp;memoir on the roots of Galamites has rendered our knowledge

� Williamson (81), vide also Spencer (81). nbsp;nbsp;nbsp;� Spencer (83), p. 459.

�� Williamson (83), p. 459, Pis. xxvii.�xxx. nbsp;nbsp;nbsp;* Kenault (85).

of Astromyelon almost complete. Some of the finest specimens, in which the organic connection between typical Calamitenbsp;stems and Astromyelon roots is clearly demonstrated, are in thenbsp;Natural History Museum, Paris. There are several sectionsnbsp;also from English material which show the connection betweennbsp;root and stem very clearly.

Casts of the hollow pith of Calamite rhizomes or aerial branches are occasionally found in which slender appendagesnbsp;are given off either singly or in tufts from the nodal regions.nbsp;Many examples of such casts have been figured by Lindley andnbsp;Huttonh Binney^, Grand�Eury^ Weiss^ Stur, and other writers�.

Fig. 90. Pith-oast of a Calamite stem, with roots; embedded in sandstone and shale. (After Grand� Eury.) Much reduced.

The large stem-cast of fig. 90 illustrates the manner of occurrence of long branched roots on the nodes of a Calamitenbsp;growing in sandy or clay soil. The lower and more darkly

1 Lindley and Hutton (31), Pis. lxxviii. and lxxix. (The specimens are figured in a reversed position.)

shaded portion of the specimen is covered by a layer of coal representing the carbonised wood and cortex, which has beennbsp;moulded on to the sandstone pith-cast. In fig. 77 (p. 316) anbsp;fairly thick root is seen, in organic connection with one of thenbsp;nodes, N 3, and on N 2 there is a scar of another root.

There are certain external characters by which one may often recognise a Calamitean root. There is no division intonbsp;nodes and internodes as in stems, and as the pith of the rootnbsp;was usually solid the parallel ribs and grooves of stem-casts arenbsp;not present. In smaller flattened roots there may sometimesnbsp;be seen a central or excentric black line representing the stele,nbsp;and the surface of the root presents a curious wrinkled ornbsp;shagreen texture, probably due to the shrinkage of the loosenbsp;lacunar cortex. The occasional excentric position of the stelenbsp;is no doubt due to the displacement of the vascular cylindernbsp;as a result of the rapid decay of the cortical tissues. In thenbsp;Bergakademie of Berlin there are some unusually good examplesnbsp;of Calamite casts bearing well-preserved root-impressions; thesenbsp;include the original specimens figured by Weiss t

No doubt some of the roots figured by various writers under the names Pinmdaria^ and HydaticP belong to Galamites,nbsp;but it is often impossible to identify detached ^pecimens withnbsp;any certainty.

The section figured diagrammatically in fig. 91 A shows the characteristic single series of large lacunae, I, in the middlenbsp;cortical region. In the centre there is a wide solid pith surrounded by a ring of vascular tissue, x. The appearance of thenbsp;middle cortex is very like that of the stem of a water-plantnbsp;such as Myriophyllum, the Water Milfoil; it shows that thenbsp;Calamite roots grew either in water or swampy gi�ound. Innbsp;fig. 91 B, the root characters are clearly seen; the centre ofnbsp;the stele is occupied hy large parenchymatous cells which arenbsp;rather longer than broad in longitudinal view; at the periphery there are four protoxylem groups px, alternating withnbsp;four groups of phloem, ph, the latter being situated a little

further from the centre of the stele. The structure is therefore that of a typical tetrach root. In the example represented in

the figure secondary thickening has begun, and the cambial cells internal to each phloem group have given rise to a fewnbsp;radially disposed tracheids, of. Beyond the phloem there arenbsp;' two la3'ers of parench3'ma representing, as regards position, anbsp;pericycle and an endodermis. In the ordinary pericycle andnbsp;endodermis of the roots of most plants the cells of the twonbsp;layers are on alternate radii, but in the Calamite root, as in

Equisetum roots, the cells of these layers are placed on the same radii, as seen in the neighbourhood of in the figure.nbsp;This correspondence of the radial walls of the endodermal andnbsp;pericyclic cells points to the development of both layers fromnbsp;one mother-layer, and suggests the � double endodermis � ornbsp;phloeoterma of Equisetum (p. 254). The cells in the outer ofnbsp;these two layers have slight thickenings on the radial wallsnbsp;recalling the usual character of endodermal cells. The phloeoterma is succeeded by a few layers of parenchyma, constitutingnbsp;the inner cortex, and beyond this we have the large lacunaenbsp;separated from one another by slender trabeculae of cells. Thenbsp;outer cortex is limited by a well-defined layer of thick-wallednbsp;cells, which may be spoken of as the epidermoidaP layer.nbsp;Roots possessing this superficial layer of thicker cells have nonbsp;doubt lost the original surface-layer which produced thenbsp;absorptive root-hairs.

The xylem elements have the form of spiral, reticulate and scalariform tracheids.

In roots or rootlets smaller than that shown in fig. 91 B, the primary xylem may extend to the centre of the stele, and formnbsp;a continuous axial strand; in such examples the structure maynbsp;be diarch, triarch or tetrach. The origin of the cambiumnbsp;agrees with that in recent roots, the ceils immediately externalnbsp;to the protoxylem tracheids become meristematic, as alsonbsp;those internal to the phloem. Another root-character is seennbsp;in the endogenous origin of lateral members. Good examples ofnbsp;branching' roots are figured by Williamson^ and by Williamsonnbsp;and Scott I

Older roots¹ are usually found in a decorticated condition. A transverse section of root in which secondary thickening hasnbsp;been active for some time presents on a superficial view a closenbsp;resemblance to a stem of Galamites, but a careful comparisonnbsp;at once reveals important points of difference. The specimen

�² For figures tiide Williamson, loc. cit., Williamson and Scott, and Renault (85), (93).

diagrammatically sketched in fig. 92 illustrates very clearly the

origin of a root from the node of a Calamite stem. The section has passed through a stem in a tangential direction, showingnbsp;the characteristic arrangement of the vascular bundles �C, andnbsp;principal medullary rays m. The small leaf-traces, t, t, affordnbsp;another feature characteristic of a Calamite stem. The portionnbsp;of stem to the right of the figure has been slightly displaced,nbsp;and between this piece and the root R, one of the ubiquitousnbsp;Stigmarian appendages, s, has inserted itself At a fairlynbsp;thick and decorticated root is seen in oblique transversenbsp;section; at the upper end the root tracheids are seen in directnbsp;continuity with the xylem of the stem. In the centre of thenbsp;root is the large solid pith surrounded by twelve bluntly pointednbsp;xylem groups, composed in the main of radially disposed scalari-form elements with narrow secondary medullary rays like thosenbsp;in a stem. Between each xylem group there is a broadnbsp;medullary ray, which tapers rapidly towards the outside, andnbsp;is soon obliterated by the formation of interfascicular secondary xylem. At R' a portion of another root is seen innbsp;transverse section, and Rquot; the inner part of a single xylemnbsp;group is shown more clearly. The solid pith and the absencenbsp;of carinal canals are the two most obvious distinguishingnbsp;features of the roots.

As Benault points out, roots of Calamites have been figured by some writers^ as examples of stems, but it is usually comparatively easy to distinguish between roots and stems. Onnbsp;examining the xylem groups more closely, one notices thatnbsp;the apex of each is occupied by a triangular group of centripetal ly-developed primary tracheids, the narrow spiral protoxylemnbsp;elements occupying the outwardly directed apex. The protoxylem apex is usually followed externally by a ray ofnbsp;one or two radially disposed series of parenchymatous cells.nbsp;This ray is not distinguished in fig. 92 Rquot; from the rows ofnbsp;xylem tracheids. Each xylem group is thus formed partly ofnbsp;centripetal xylem and in part of secondary centrifugal xylem;nbsp;the latter is associated with secondary medullary rays, as innbsp;stems, and contains a broader ray {fascicular ray of Williamson

and Scott immediately opposite each protoxylem strand. In the roots of recent plants {e.g. Cuciirbita, Phaseolus, amp;c.) anbsp;broad medullary ray is often found opposite the protoxylem,nbsp;and such an arrangement is a perfectly normal structure innbsp;roots

Renault has recently described several species of Calamite roots which he designates by specific names, some of themnbsp;belonging to stems with the Arthropitys structure, and othersnbsp;to Calamodendron. Some of the roots figured by the Frenchnbsp;author have an axial strand of xylem with 7�15 projectingnbsp;angles of protoxylem^. These he considers true roots, but thenbsp;larger specimens with a wide pith he prefers to regard as stolons.nbsp;In the latter he mentions the union of the primary centripetal with the secondary centrifugal wood as a distinguishingnbsp;feature. It has been shown, however, that each group ofnbsp;secondary xylem includes a median ray of parenchyma, and thatnbsp;the whole structure is essentially that of a root, and not that ofnbsp;a modified stem or stolon. The organs described by Renaultnbsp;as true roots are probably rootlets, and as Williamson andnbsp;Scott have demonstrated, there is every gradation between thenbsp;smaller specimens with a solid xylem axis and those with anbsp;large central pith.

It is interesting to note that Renault�s figures of Calamodendron roots show the closest resemblance to those of the subgenus Arthropitys.

The occurrence of fossil plants in the form of isolated fragments is a constant source of difficulty, and is well illustratednbsp;by tbe numerous examples of strobili which cannot be connected with their parent stems. We are, however, usuallynbsp;able to recognise Calamitean cones if the impressions ornbsp;petrified specimens are fairly well preserved, but it is seldomnbsp;possible to correlate particular types of cones with the corresponding species of foliage-shoots or stems. Palaeobotanical

literature contains numerous illustrations and descriptions of long and narrow strobili designated by different generic termsnbsp;such as Volkmannia, Brukmannia, Galamostachys, Macro-stachya and others; many of these have since been recognisednbsp;as the cones of Calamites, while some species of Volkmannianbsp;have been identified with Sphenophyllum stems. Before furthernbsp;considering the general question of Calamite cones, a fewnbsp;examples may be described in detail as types of fructificationnbsp;which are known to have been borne by Calamites. Thenbsp;examples selected are species of the two provisional genera.nbsp;Galamostachys and Palaeostachya.

The usual form of a Calamite. cone is illustrated in fig. 93, which represents a fertile shoot bearing a few narrow linearnbsp;leaves of the Galamocladus type ; in the axils of some of thesenbsp;are borne the long strobili.

In 1867 Carruthers^ gave an account of the structural features of the species of cones named by him Volkmannianbsp;Ludwigi and V. Binneyi, the generic term having been originally used by Sternberg^ for some impressions of Carboniferousnbsp;strobili. Brongniart� in 1849 referred to the various forms ofnbsp;Volkmannia as cones of Asterophyllitean branches, and thenbsp;latter he regarded as the foliage-shoots of a Calamite stem.nbsp;In 1868 Binneyi published a description, with several illustrations, of the cones named by Carruthers Volkmannia Binneyi,nbsp;and referred to them as the fructification of that type ofnbsp;Calamite stem spoken of in a previous section of thisnbsp;chapter (p. 311) as Calamites (Arthropitys) communis (Binney).nbsp;This cone is now usually spoken of as Calamostachys Binneyana] the specific name BinneyanahCmg suggested by Schimper*^nbsp;in 1869 as more euphonious than that proposed by Carrhthers.nbsp;In recent years our knowledge of both C. Binneyana andnbsp;G. Ludwigi has been considerably extended. We shall confinenbsp;our attention in the following account to the former species�.nbsp;Some excellent figures of the latter species may be found innbsp;Weiss� Memoir�� on Calamarieae.

One of the largest examples of Calamostachys Binneyana so far recorded has a length of 3�4 cm. and a maximumnbsp;diameter of about 7'5 mm. The axis of the cone bears whorlsnbsp;of sterile leaves or bracts at equal distances; the linear bractsnbsp;of each whorl are coherent basally as a disc or plate ofnbsp;tissue attached at right angles to the central axis of the cone.nbsp;The periphery of each of these discs divides up into twelvenbsp;linear segments, which curve upwards in a direction more ornbsp;less parallel to the strobilus axis, and at right angles to the

� For figures and descriptions of this type of cone vide Williamson (73), (80), (89); Hick (93), (94) and Williamson and Scott (94).

coherent portion of each whorl. The manner of occurrence of the whorls is shown in fig. 94, which has been sketchednbsp;from a large section in the Williamson collection. The segments of the successive sterile verticils alternate with onenbsp;another, so that in the surface-view of a cone the long andnbsp;narrow free bracts appear spirally disposed. Midway between

Fig. 94. Calamostachys Binneijana (Carr.) in longitudinal (radial and tangential) section. nbsp;nbsp;nbsp;'

these alternating sterile verticils there is a series of fertile appendages, also given off in regular whorls. Each fertilenbsp;whorl consists of about half as many members as the segments

^of a sterile whorl, and the members of the several fertile whorls are superposed and not alternate. Each member has the formnbsp;of a stalk or sporangiophore given off at right angles from thenbsp;cone axis ; this is expanded distally into a peltate disc bearingnbsp;four sporangia attached to its inner face. In fig. 94 we can onlynbsp;see the basal portions of the sporangiophores, which are shownnbsp;in the upper part of the sketch as pointed projections, Sp, fromnbsp;the cone axis. Each sporangiophore is traversed by a vascularnbsp;strand which sends off a branch to the base of a sporangiumnbsp;(fig. 95, A, t).

The axis of the cone is occupied by a single stele, usually � triangular in section; the stele consists of a solid pith ofnbsp;elongated cells surrounded by six vascular bundles, two atnbsp;each corner. A somewhat irregular gap marks the positionnbsp;of the protoxylem of each strand, and portions of spiral ornbsp;annular tracheids may occasionally be seen in the cavity.nbsp;These cavities, which may be spoken of as the carinal C9,nals,nbsp;disappear at the nodes, where there is a mass of short reticu-lately pitted tracheids, as in a Calamite stem. Vascular bundlesnbsp;pass upwards in an oblique direction from the central stelenbsp;to supply the bracts, each of which is traversed by a singlenbsp;strand of tracheids. The coherent portion, or disc, of eachnbsp;sterile whorl consists of sclerenchymatous elements towardsnbsp;the upper surface, and of parenchyma below. The pedicel ofnbsp;the sporangiophores consists of fairly thick-walled cells traversednbsp;by a single vascular strand, and the peltate distal portions arenbsp;made up of parenchymatous cells arranged in a palisade-likenbsp;form at right angles to the free surface of the sporangiophores.nbsp;The vascular strand of the pedicel forks into two halves justnbsp;below the peltate head, and these branches again bifurcate tonbsp;send a branch to each sporangium. The four sporangia ofnbsp;each sporangiophore are attached by a narrow band of tissuenbsp;to the shield-shaped distal expansion (fig. 95, A).

In a tangential section of a cone, such as the lower portion of fig. 94 and in fig. 95, B, the sporangiophores present thenbsp;appearance of narrow stalks (fig. 95, B, a) in the middlenbsp;of a cluster of sporangia, and the latter appear more or lessnbsp;square in outline. The wall of a sporangium is made of a

single layer of cells (fig. 95, B) which present a characteristic appearance in surface-view (fig. 95, C), the thin walls being

crossed at right angles by small vertical plates. In the tangential section of the coherent sterile whorls (fig. 95, B,nbsp;b and b) the vascular strands are occasionally seen innbsp;transverse section (fig. 95, B, t), as they pass outwards to thenbsp;several free bracts.

The spores in Galamostachys Binneyana are all of the same size, and no macrospores have ever been seen. In well preserved specimens tetrads of spores may be seen, still enclosed bynbsp;the wall of the spore-mother-cell (fig. 95, A and D); and the tornnbsp;remnants of the mother-cell sometimes simulate in appearancenbsp;the elaters of an Equisetum spore. In surface-view a sporenbsp;often shows clearly the three-rayed marking, which is a characteristic feature of daughter-cells formed in a tetrad from a

mother-cell. The spores of a tetrad are in some cases of unequal size, some having developed more vigorously thannbsp;others. This unequal growth and nourishment of spores isnbsp;clearly shown in fig. 96, which represents a sporangium of anbsp;heteroporous Oalamitean strob'ilus, C. Casheana. Williamsonnbsp;and Scott ^ have described striking examples of spores innbsp;different stages of abortion, and these authors draw attentionnbsp;to the importance of the phenomenon from the point of viewnbsp;of the origin of a heterosporous form of cone. The abortionnbsp;of some of the members of a spore-tetrad and the consequentnbsp;increased nutrition of the more favoured daughter-cells, mightnbsp;well be the starting-point of a process, which would ultimatelynbsp;lead to the production of well defined macrospores and microspores. The young microsporangia and macrosporangia ofnbsp;recent Vascular Cryptogams such as Selaginella, Salvinia andnbsp;other heterosporous genera are identical in appearance^; it isnbsp;not until the spore-producing tissue begins to differentiato-intonbsp;groups of spores, that the sporangia assume the form of macrosporangia and microsporangia. During the evolution of thenbsp;various known types of pteridophytic plants heterospory gradually succeeded isospory, and this no doubt occurred severalnbsp;times and in different phyla of the plant kingdom. In thenbsp;mature sporangia of some of the Oalamitean strobili we havenbsp;in the inequality of the spores in one sporangium an indicationnbsp;of the steps by which heterospory arose; and in the immaturenbsp;sporangia of some recent genera we are carried back to a stagenbsp;still nearer the starting-point of the substitution of the heterosporous for the isosporous condition.

To Williamson� again is largely due the information we possess as to the structure of this type of Oalamitean strobilus.nbsp;Its special interest lies in the occurrence of macrospores andnbsp;microspores in the same cone.

The strobilus axis agrees in structure with that of G. Binneyana, but in G. Gasheana a band of secondary xylemnbsp;forms the peripheral portion of the triangular stele. Werenbsp;any further proof needed of the now well-established fact thatnbsp;secondary growth in thickness is by no means unknown as annbsp;attribute of Vascular Cryptogams, the co-existence in the samenbsp;cone of a cambium layer producing secondary wood and bark,nbsp;and cryptogamic macrospores and microspores, affords conclusive evidenced The dogma accepted by many writers fornbsp;a considerable number of years that the power of secondarynbsp;thickening is evidence against a cryptogamic affinity, has beennbsp;responsible for no little confusion in palaeobotanical nomenclature.

On the axis of Galamostachys Gasheana there are borne alternate whorls of fertile and sterile appendages similar tonbsp;those in the homosporous G. Binneyana, but they are inclinednbsp;more obliquely to the axis of the cone. Macrospores andnbsp;microspores have been found in sporangia borne on the samenbsp;sporangiophore.

1 An excellent figure illustrating the co-existence of hetero.spory and secondary thickening is given by Williamson and Scott, loc. cit., PI. lxxxii.nbsp;fig. 36.

aborted sister-cells like those noticed in C. Binneyana] this phenomenon is well illustrated by the unequally nourishednbsp;spores in the sporangium of fig. 96, but no such starved sporesnbsp;have been found in the microsporangia. In this cone, then,nbsp;heterospory has become firmly established, but the occurrencenbsp;of undersized spores in a macrospore-tetrad leads us back tonbsp;the probable lines of development of heterospory, which arenbsp;seen in C. Binneyana at their starting-point.

In the two species of strobili which have been described, Calamostachys Binneyana and C. Casheana, the sporangiophoresnbsp;or sporophylls are given off at right angles to the axis, andnbsp;midway between the sterile whorls. These are two of thenbsp;most important distinguishing features of the Calamitean conesnbsp;included under the generic term Calamostachys. In anothernbsp;form of cone, which also belongs to Calamitean stems, thenbsp;sporangiophores arise in the axil of the sterile leaves, and arenbsp;inclined obliquely to the axis of the cone. To this type thenbsp;generic name Palaeostachya has been applied by the latenbsp;Prof. Weiss' of Berlin. The portion of a cone shown in fig. 97nbsp;shows the arrangement of the sterile and fertile appendagesnbsp;characteristic of Palaeostachya.

It is practically impossible to distinguish between cones of the Calamostachys and Palaeostachya type in the case ofnbsp;imperfectly preserved impressions ; indeed we cannot assumenbsp;that all long and narrow cones with spirally disposed ver-ticillate hracts are Calamitean. We must have the additionalnbsp;' Weiss (76), p. 103.

evidence of internal structure or of the direct association of the cones with Calamitean foliage.

In 1869 Williamson^ described a fragment of a strobilus which showed certain anatomical features indicative of a closenbsp;relationship or even identity with Galamites. Some years later ^nbsp;a much more perfect example was obtained from the Coal-Measures of Lancashire, and the additional evidence which itnbsp;afforded definitely confirmed the earlier views of Williamson.nbsp;The cone was more fully described by Williamson in 1888,nbsp;as �the true fruit of Galamites.� It is clearly a form ofnbsp;Weiss� genus Palaeostachya-, Williamson and Scott* refer tonbsp;it in their Memoir as Galamites pedunculatus. It is preferable,nbsp;however, to retain the generic designation Palaeostachya fornbsp;cones of this type. As the name P. pedunculata has previously been adopted by Weiss^ for a cone figured by Williamson� in 1874, and afterwards referred to by that author innbsp;writing as P. pedunculata, it is proposed to substitute thenbsp;specific name vera; this specific name being chosen with anbsp;view to put on record the fact that it was this type of conenbsp;that Williamson first proved to be the true fructificationnbsp;of the Calamite.

The axis of P. vera is practically identical in structure with a Calamitean twig. There is a hollow pith in the centre of thenbsp;stele surrounded by a ring of 16�20 collateral bundles, eachnbsp;of which is accompanied by a carinal canal as in a vegetativenbsp;shoot. As the pedicel of the strobilus passes into the conenbsp;proper it undergoes some modification in structure, but retainsnbsp;the characteristic features of a Calamite. The diagrammaticnbsp;longitudinal section of fig. 98, which is copied from a drawingnbsp;by Williamson�, shows the broadening of the vascular strandsnbsp;at the nodes, and here and there a carinal canal is seen internalnbsp;to the wood.

The axis of the cone bears whorls of bracts at right angles to the central column. Each whorl consists of about 30�40

segments coherent basally into a disc of prosenchymatous and parenchymatous tissue. The free linear bracts curve sharplynbsp;upwards from the periphery of the disc, approximately parallelnbsp;to the axis of the cone. From each of these sterile whorlsnbsp;there are given off 16�20 long and slender obliquely-inclinednbsp;sporangiophores, sp, which arise from the upper surface of thenbsp;disc close to the axis. Each sporangiophore no doubt bore fournbsp;sporangia, S, containing spores of one size,�about '0*7 5 mm. innbsp;diameter. The specimens of Palaeostachya vera so far obtainednbsp;do not show the actual manner of attachment of the sporangia,nbsp;but more complete examples of other species of Palaeostachya^nbsp;enable us to assume with certainty that the sporangiophoresnbsp;terminated in a distal peltate expansion bearing four sporangianbsp;on its inner face.

A transverse section of the axis of the cone in the region of the sterile and fertile appendages shows the vascular bundlesnbsp;arranged in pairs. In a section through the peduncle of thenbsp;cone, below the lowest whorl of bracts, the bundles of the stelenbsp;are situated at equal distances apart. The cortical tissue of thenbsp;peduncle is traversed by a ring of large canals^ similar to thenbsp;vallecular canals of an Equisetum stem.

Isospory is not a constant characteristic of Palaeostachya; some forms have been found with macrospores and microspores^.

Other Galamitean cones, and exam/pies illustrating the connection hekveen Cones and Vegetative Shoots.

It would be out of place in an introduction to Palaeobotany to attempt an exhaustive account of the various cones whichnbsp;were probably borne by Galamitean plants, but there are a fewnbsp;general points to which the attention of the student should benbsp;directed. The examples dealt with in the foregoing descriptionnbsp;illustrate the fact, that plants included under the comprehensivenbsp;genus Galamites bore cones possessing distinct morphologicalnbsp;features. There are, however, other types of strobili whichnbsp;have been found in organic connection with Galamites', andnbsp;some of these must be taken into account in dealing withnbsp;Calamarian plants. The genera Volkmannia, Brukmannia, Hut-tonia, Macrostachya, in addition to Galarnostachys and Palaeostachya and others, have been applied by different writers tonbsp;Galamitean cones. As Solms-Laubach� has suggested, it isnbsp;wiser to discard Volkmannia and Brukmannia, as they havenbsp;been made to do duty for cones of widely different forms.nbsp;It is better to adhere to the provisional generic names used bynbsp;Weiss, as they enable us to conveniently systematise the variousnbsp;Calamarian strobili.

The following classification may be given of the better known cones, some of which we are able to describe innbsp;considerable detail, while others are still very imperfectlynbsp;known. We have good evidence that all these strobili were

borne by vegetative shoots of the type of Oalamites, Gala-mocladus or AnnvXaria.

Cones long and narrow, consisting of a central axis bearing alternate whorls of sterile and fertile appendages, the latternbsp;having the form of sporangiophores attached at right anglesnbsp;to the axis midway between the sterile verticils, and bearingnbsp;four sporangia on the inner face of a peltate distal expansion.

Galamostachys Binneyana Schimp., G. Ludwigi Carr., G. Gasheana Will., may be referred to as examples of this type ofnbsp;cone; also some of the strobili described by different authors asnbsp;species of Volkmminia^, Brukraannia^, amp;c.

Although one cannot make out the detailed structure of a Calamite cone in the absence of internal structure, it is oftennbsp;possible to recognise the essential features in specimens preserved in ironstone nodules, such as those from Coalbrook Dalenbsp;in Shropshire, or by carefully examining the carbonised impressions on shale under a simple microscope.

Weiss applies the term Paracalaniostachys* to cones of the Galamostachys form, but in which the manner of attachmentnbsp;cannot be made out. Such a cone as that of fig. 93 shouldnbsp;probably be referred to this sub-type of Galamostachys in thenbsp;absence of definite evidence as to the position of the sporangia.

Another term Stachannularia, originally used by Weiss as a genus�, was afterwards� applied to cones of the same generalnbsp;type as Galamostachys, in which the sporangiophores havenbsp;the form of thorn-like structures bearing on their upper sidenbsp;a lamellar expansion. There is however some doubt as to thenbsp;correct interpretation of the features associated with conesnbsp;included in Stachannularia', for an account of such forms

- E.g. 'Eolkmaimia Ludwigi Carr., also Volhmannia elongata Presl. [Solms (91), p. 332 and Weiss (76), p. 108].

reference must be made to the writings of Weiss, Renault h Solms-Laubach^ and others^

Calamostachys cones have been found in organic union with branches bearing leaves of the Annularia type, also withnbsp;Galamocladus foliage, and the branches bearing such conesnbsp;have been found in actual connection with Calamitean stems.nbsp;The association of cones and vegetative stems and branches isnbsp;shown in tabular form on p. 363.

In this genus the general habit agrees with that of Calamostachys, and in imperfectly preserved specimens it maynbsp;be impossible to discriminate between Calamostachys andnbsp;Palaeostachya. The latter form is characterised by the attachment of the sporangiophores in the axil of the sterile bracts,nbsp;or immediately above them, as shown in figs, 97 and 98.

Examples. Palaeostachya vera sp. nov., P. pedunculata Will, afford examples of this form of strobilus. The genus Palaeostachya includes several species previously described under thenbsp;genus Volkmannia^.

Strobili of this generic type are known in organic association with Annularian branches, as well as with Galamocladus andnbsp;Galamites.

This generic name was originally applied by Schimper� to certain forms of Calamitean stems, of the type afterwardsnbsp;referred to the sub-genus Galamitina by Weiss, bearing longnbsp;and thick cones. The name is, however, more appropriatelynbsp;restricted to strobili, which differ from the two preceding generanbsp;in their greater length (14�16 cm.) and in the more crowdednbsp;and imbricating whorls of bracts. The internodes of thenbsp;cones are very short, and each whorl of bracts consists of aboutnbsp;20 coherent members separated at the periphery of the disc

into short pointed teeth. The internal structure of Macrostachya has not been satisfactorily determined. An account by Renault^nbsp;of a petrified specimen does not present a very clear idea as tonbsp;the structural features of this form of Calamitean strobilus.

The generic name Huttonia, suggested by Sternberg^^ in 1837, is applied to cones which closely resemble Macrostachyanbsp;in habit, but differ�so far as our scanty knowledge enables usnbsp;to judge�in the arrangement of the members. The student

* nbsp;nbsp;nbsp;Weiss (84), PI. xx. fig. 6.nbsp;nbsp;nbsp;nbsp;* Weiss (84), PL xx. fig. 7; PL xxi. fig. 4.

must refer to Weiss^, Solms-Laubach- and other writers^ for a further account of these types, and of another rare and little-known form of cone, called by Weiss Gingularia*.

Macrostachyan cones have been found attached to stems of Galamites which are included in the sub-genus Galamitinanbsp;(p. 367). The larger size of Macrostachya as a distinguishingnbsp;feature is not always a safe test; some cones which belong tonbsp;Palaeostachya [e.g. P. arhorescens Sternb.] and Galamostachysnbsp;(e.g. G. Solmsi) are much thicker and larger than the majoritynbsp;of species of these two genera.

It would appear from the examples selected to illustrate the connection between strobili and vegetative shoots, that thenbsp;Annularia type of branch usually bears cones which conformnbsp;to the genus Galamostachys (Stachannularia)-, while the As-terophyllitean branches�Calamocladus�are associated withnbsp;Palaeostachya and Macrostachya. .But this rule is not constant, and we are not in a position to speak of cones of anbsp;particular type as necessarily characteristic of definite types ofnbsp;Calamitean shoots.

Although it is admitted by the great majority of Palaeo-botanists that the Galamites were all true Vascular Cryptogams, the older view that some members of the Calamarieae arenbsp;gymnospermous has not been given up by Renault^ Thisnbsp;observer has recently described some seeds which he believesnbsp;were borne by Calamitean stems; he admits, however, that nonbsp;undoubted female cones of Galamodendron have so far beennbsp;found. In view of the unsatisfactory evidence on which Renault�snbsp;opinion is based, we need not further discuss the questionsnbsp;which he raises.

[The following specimens in the Williamson Cabinet in the British Museum, may be found useful in illustration of the structure of Catamites.

Stems, (i. Arthropitys.) Young twigs and small branches 1, 2, 6, 10, 14, 19, lie* 1002, 1007, 1020.

Older stems {transverse sections) 15-17, 62, 77-87, 115 �, 117*, 118*, 120, 122*-124* 1933 a, 1934, 1941.

(Radial sections) 20, 20 a, 21, 22, 48, 65-68, 83-91,137* 138*, 1937. (ii. Arthrodendron) 36, 37, 38, 52, 54.

Strohili. i. Calamostachys Binneyana. 991, 996, 997, 1000, 1003, 1005, 1007, 1008, 1011, 1013, 1016, 1017, 1022, 1023, 1037 a, 1043.

III. Pith-casts of Calamites.

Palaeobotanical literature contains a lai'ge number of species of Calamites founded on pith-casts alone. Many of these so-called species are of little or no value botanically, but while wenbsp;may admit the futility of attempting to recognise specific typesnbsp;in the same sense as in the determination of recent plants, it isnbsp;necessary to pay attentibn to such characters as are likely tonbsp;prove of value for descriptive and comparative purposes. Fromnbsp;the nature of the specimens it is clear that many of thenbsp;differences may be such as are likely to be met with innbsp;different branches of the same species, while in others thenbsp;pith-casts of distinct species or genera may be almost identical.

The most striking differences observable in Calamite casts are in the character of the internodes, the infranodal canals,nbsp;the number and disposition of branch-scars, and other surfacenbsp;features. Occasionally it is possible to recognise certain anatomical characters in the coaly layer which often surrounds anbsp;shale- or sandstone-cast, and the surface of a well preserved castnbsp;may give a clue to the nature of the wood in the faint outlinesnbsp;of cells which can sometimes be detected on the cast itself!nbsp;The breadth of the carbonaceous envelope on a cast has beennbsp;frequently relied on by some writers as an important character.nbsp;It has been suggested^ that we may arrive at the originalnbsp;thickness of the wood of a stem by measuring the coaly layernbsp;^ Zeiller (88), PI. liv. fig. 4.nbsp;nbsp;nbsp;nbsp;^ Stiir (87), p. 17.

and multiplying the breadth by 27 ; the explanation being that a zone of wood 27 mm. in thickness is reduced in the process ofnbsp;carbonisation to a layer 1 mm. thick.

The breadth of the coal on the same form of cast may vary considerably; on this account, and for various other reasons,nbsp;such a character can have but little value. Our knowledge ofnbsp;anatomy may often help us to interpret certain features ofnbsp;internal casts and to appreciate apparently unimportant details.nbsp;One occasionally notices that a Calamite pith-cast has largenbsp;infranodal canals, and in some specimens each internodal ridgenbsp;may be traversed by a narrow median line or small groove;nbsp;large infranodal canal casts suggest the type of stem referrednbsp;to the subg^nus Arthrodendron, and the median line on thenbsp;ridges may be due to bands of hard tissue in each principalnbsp;medullary ray.

In attempting to identify pith-casts the student must keep in view the probable differences presented by the branchingnbsp;rhizome, the main aerial branches and the finer shoots of thenbsp;same individual. The long internodal ridges of some casts maynbsp;be mistaken for the parallel veins of such a leaf as Cordaites, anbsp;Palaeozoic Gymnosperm, if there are no nodes visible on thenbsp;specimen. The fossil figured by Lindley and Hutton^ asnbsp;Poacites, and regarded by them as a Monocotyledon, is nonbsp;doubt a portion of a Calamite with very long internodes. Annbsp;interesting example of incorrect determination has recentlynbsp;been pointed out by Nathorst'^ in the case of certain castsnbsp;from Bear Island, originally described by Heer as examples ofnbsp;Galamites] the vertical rows of leaf-trace casts on a Knorrianbsp;were mistaken for the ribs of a Calamite stem. The specimensnbsp;in the Stockholm Museum fully bear out Nathorst�s interpretation. The undulating course of internodal ridges andnbsp;grooves is not in itself a character of specific value. If anbsp;Calamite stem were bent slightly, the wood and medullary-raynbsp;tissues on the concave side might adapt themselves to thenbsp;shortening of the stem by becoming more or less folded, and a

^ Lindley and Hutton (31), PI. cxliib. The original specimen is in the University College Collection, London.

cast of such a stem would show undulating ridges and grooves on one side and straight ones on the other^.

A convenient classification of Calamite casts was proposed by Weiss in 1884, founded chiefly on the number and mannernbsp;of occurrence of branch-scars�or rather branch-depressions�nbsp;on the surface of pith-casts. Weiss^ recognised the imperfection of his proposed grouping, and Zeiller* has also expressednbsp;reasonable doubts as to the scientific value of such group-characters. Weiss instituted three subgenera�Calamitina,nbsp;Eucalamites and Stylocalamites, which are made use of asnbsp;convenient terms in descriptive treatment of Calamite casts.nbsp;The following account of a few of the more typical casts maynbsp;serve to illustrate the methods employed in the description ofnbsp;such specimens; the synonomy given for the different speciesnbsp;is not intended to be complete, but it is added with a view tonbsp;drawing attention to the necessity for careful comparison innbsp;systematic work.

This sub-genus of Galamites, as instituted by Weiss'*, includes Calamitean stems or branches, which are characterisednbsp;by the periodic occurrence of branch-whorls usually representednbsp;by fairly large oval or circular scars just above a nodal linenbsp;(figs. 99, 100 and 101). The branch-scars may form a row ofnbsp;contiguous discs, or a whorl may consist of a smaller numbernbsp;of branches which are not in contact basally. A form describednbsp;by Weiss as G. pauciramis, Weiss'*, has only one branch in eachnbsp;whorl, as represented by a single large oval scar on some of thenbsp;nodes of the cast. A stem of this form is by no means a typicalnbsp;Calamitina, but it serves to show the existence of forms connecting Weiss� sub-genera Calamitina and Eucalamites. Thenbsp;number of internodes and nodes between the branch whorlsnbsp;varies in different specimens, and is indeed not constantnbsp;in the same plant. Each nodal line bears numerous ellipticalnbsp;scars which mark the points of attachment of leaves; each

'* Seward (88). nbsp;nbsp;nbsp;^ Weiss (84), p. 54.nbsp;nbsp;nbsp;nbsp;* Zeiller (88), p. 329.

-* Weiss (76), p. 117; (84), p. 55. nbsp;nbsp;nbsp;� Weiss (84), p. 93, Pi xi. fig. 1.

branch-whorl is situated immediately above a node, and in some forms this nodal line pursues a somewhat irregular coursenbsp;across the stem, following the outlinesnbsp;of the several branch-scarsh Thenbsp;surface of the internodes is eithernbsp;perfectly smooth or it is more frequently traversed by short longitudinal ridges or grooves probabl}-representing fissures in the barknbsp;of the living stem; these are indicated by lines in fig. 99 and bynbsp;elongated elliptical ridges in fig. 101.

On young stems the leaves are occasionally found in place, as fornbsp;example in an example figured bynbsp;Weiss^ {G. G�pperti), or we may havenbsp;leaf-verticils still in place in muchnbsp;older and thicker branches* (cf. fig.

It occasionally happens that the bark of Galamitina stems has been 99- Caiamites (Calamitina)nbsp;preserved as a detached shellquot;* re- G�pperti{Ett.). 6, branch scars.

minding one of the sheets of Birch Manchester Museum, Owens bark often met with in forests, the College, i nat. size,nbsp;separation being no doubt due in

the fossil as in the recent trees to the manner of occurrence of the cork-cambium.

In a few cases branches have been preserved still attached to a stem or branch of higher order; examples of such specimens arenbsp;figured by Bindley and Hutton*, Stur�, and others. Grand�Eury'nbsp;has given an idealised drawing of a typical Calamitina bearingnbsp;a whorl of branches with the foliage and habit of Asterophyllitesnbsp;equisetiformis. The specimen on which this drawing is based

is in the Natural History Museum, Paris; it shows Astero-phyllitean branches in organic connection with a Calamitean stem, but it is not quite clear if the stem is a true Galamitina.nbsp;A large drawing of this interesting specimen is given by Stur*nbsp;in his monograph on Galamites, also a smaller sketch bynbsp;Renault^ in his Cours de botanique fossile. Similar branchesnbsp;of the Asterophyllites type attached to an undoubted Cala-mitina are figured also by Lindley and Hutton. There is, innbsp;short, good evidence that stems of this sub-genus bore branchesnbsp;with Asterophyllitean shoots.

The wood of stems of the Galamitina group of Galamites, in some instances at least, was of the Arthropitys type; thisnbsp;has been shown to be the case in some French specimens fromnbsp;the Commentry coal-field� and in others described by Sturhnbsp;The pith-casts of Galamitina are characterised by comparativelynbsp;short internodes separated by deep nodal constrictions, as shownnbsp;in fig. 100. From Permian specimens from Neu Paka innbsp;Bohemia, described by Sturh we learn that there were the usualnbsp;Calamite diaphragms bridging across the wide pith-cavity atnbsp;each node. Such a cast as that shown in fig. 100 is often referred to as Galamites approximatus Brongn.; the length of thenbsp;internodes and the periodic occurrence of branch-scars in thenbsp;form of circular or oval depressions along a nodal line enable usnbsp;to recognise the Galamitina casts. Weissquot; points out that innbsp;pith-casts of this form the branch-scars occur on the nodalnbsp;constriction, and not immediately above the node as is the casenbsp;on the surface of a typical Galamitina. This distinction isnbsp;however of little or no value; the point of attachment of anbsp;branch may be above the nodal line, while on the pith-castnbsp;of the same stem the point of origin of the vascular bundlesnbsp;of the branch is on the nodal constriction''.

The specimen shown in fig. 100 illustrates the appearance of a Galamitina cast. There is a verticil of branch-scars on the

lowest nodal constriction ; on the right of the pith-cast the broad band of wood is faintly indicated by the smooth surface of the

i '.i.iliSli,

1'' '�.yniiilii

I ' '�OUii

Pie. 100. Galamites (Calamitina) approximatus Brongn. Lower Coal-Measures of Ayrshire.

rock (x). Other examples demonstrating the existence of a broad woody cylinder in Calamitina. stems have been figured by Weiss^nbsp;and other writers, and some good examples may be seen in thenbsp;British Museum.

We have so far noticed the connection of certain forms of pith-casts {e.g. Galamites approximatus), and Asterophylliteannbsp;shoots with stems of the sub-genus Calamitina.

As regards the strobili our knowledge is far from satisfactory. Stur^ figures some fertile branches bearing long and narrow

strobili, either Palaeostachya or Galaniostachys, in close association with Calaniitina stems, and Renault and Zeiller* give illustrations of the association of Calaniitina steins with largenbsp;strobili of the Macrostachya form.

Before Weiss proposed the term Galamitina, various authors had figured this form of Calamite under a distinctnbsp;generic name (e.g. Hippurites of Bindley and Hutton^nbsp;Cyclocladia^, Macrostachya^, amp;c.). Stems of this type have alsonbsp;been described by more recent writers under different names,nbsp;and considerable confusion has been caused by the use ofnbsp;numerous generic designations for forms of Galamitina. Somenbsp;small fragments of Galamitina stems were described by Salter'*nbsp;in 1863 as portions of a new species of the Crustaceannbsp;Eurypterus {E. mammatus). In 1869 Grand'Eury proposednbsp;the generic name Calamophyllites^ for stems bearing verticilsnbsp;of Asterophyllites shoots; his description of such stems agreesnbsp;with Weiss� Galamitina, but as Grand�Eury�s name is used innbsp;a narrower sense as implying a connection with Asterophyllites,nbsp;it is more convenient to adopt Weiss� term in spite of thenbsp;priority of Calamophyllites. In the Fossil flora of Gommentrynbsp;we find some flattened stems of the Galamitina type describednbsp;under different generic names, as Arthropitys approximatus��nbsp;and as Macrostachya^.

The determination of distinct species of the sub-genus Galamitina is rendered almost hopeless by the variation in thenbsp;different branches of the same individual, and by the difficultynbsp;of connecting surface-impressions with casts of the pith-cavity.

A typical example of the Galamitina type of Catamites was figured by Sternberg*� in 1821 as Catamites varians. This hasnbsp;been adopted by Weiss� as a comprehensive species including

- Lindley and Hutton (31), PI. cxiv. and PI. cxc. The original specimens are in the Natural History Museum, Newcastle-on-Tyne.

Salter (63), figs. 6 and 7. Vide also Carruthers in Woodward, H. (72), p. 168. � Grand�Eury (69); vide also (77) and (90).

^ Renault and Zeiller (88), Pt. ii. Pis. lii. and cm. nbsp;nbsp;nbsp;� Ibid. PI. li.

several different � forms � of stems, which differ from Sternberg�s fossil in such points as the number of nodes between thenbsp;branch-whorls and the number of branches in each whorl. Thenbsp;result of this system of nomenclature is the separation of portionsnbsp;of one specific type under different form-names. It must benbsp;clearly recognised that accurate specific diagnoses are practicallynbsp;impossible when we have to deal with fragments of plants,nbsp;some of which are mere pith-casts, while others show the surfacenbsp;features. The specimen represented in fig. 99 agrees with anbsp;stem described by Ettingshausen^ in 18.55 as Calamites G�pperti,nbsp;and as a matter of convenience a member of the Calamitinanbsp;group showing such characters may be referred to as Calamitesnbsp;{Calamitina) G�pperti (Ett.). The following list, which includesnbsp;a few synonyms of this form, may suffice to illustrate thenbsp;difficulties connected with accurate systematic determinations.

This species is characterised by the smooth bark, which may be traversed by a few irregular longitudinal fissures; most ofnbsp;the nodes bear a series of small leaf-scars, and at fairly regularnbsp;intervals a node is immediately succeeded by a circle ofnbsp;contiguous branch-scars, 8�12 in a whorl. The pith-cast ofnbsp;this type of stem has short ribbed internodes separated by

rather deep nodal constrictions; the branch-whorls being represented by a series of pits on the nodal constrictions recurring at corresponding intervals to the whorls of branch-scars on thenbsp;surface of the stem. Leaves narrow and linear in form, likenbsp;those on Asterophyllitean branches, are occasionally associatednbsp;with this type of stem.

The fragment of a Calamitina stem shown in fig. 101 is the counterpart of a specimen originally figured by Steinhauer' innbsp;1818 as a species of Phytolithus. This may be specificallynbsp;identical with G. Gopperti; but it is better to speak of so smallnbsp;a specimen as merely one of the Ca.la^nitina stems, to be compared with Calamites (Calamitina) Gopperti. The specimennbsp;measures 14'.5 cm. in length and 7 cm. in breadth.

The form of pith-cast represented in fig. 100 is no doubt that of one of the Calamitina species, but as it is seldom possible tonbsp;determine the connection between such casts and the particular

species of sterns to which they heloiag, they are often referred to as Calamites (Calamitina) approximatus (Brongn.). Thenbsp;specimen of which fig. 100 is a photograph was originallynbsp;described and figured by Mr Kidston' from the lower Coal-Measures of Ayrshire. Both Calamites (Calamitina) G�ppertinbsp;(Ett.) and G. (Calamitina) approximatus (Brongn.) are recordednbsp;from the Transition, Middle and Lower Coal-Measures^

In the members of this sub-genus the branch-scars are either irregular in their occurrence or absent. In some Calamites the branch-scars are very few and far between, and othernbsp;species appear to have been almost without branches ; pith-castsnbsp;of such stems may be referred to the sub-genus Stylocalamites^.

An exceedingly common Calamitean cast, G. Suckotvi Brongn. (fig. 82) affords a good illustration of this type of stem. Innbsp;the specimen shown in fig. 82 we have a cast of a rhizome,nbsp;which is rather exceptional in showing three branches innbsp;connection with one another. The appearance of the fossilnbsp;suggests a rhizome, rather than an aerial shoot, bearing lateralnbsp;branches; the narrowing of the branches and the rapidnbsp;decrease in the length of the internodes towards the point ofnbsp;attachment being features associated with rhizomes rather thannbsp;with aerial branches.

Casts of Galamites Suckowi are characterised by flat or slightly convex internodal ridges separated by shallow depressions, the ridges are rounded at the upper end of each internode,nbsp;and usually bear circular casts of infranodal canals. There arenbsp;some unusually large examples of casts of this species in thenbsp;British Museum from the Radstock Coal-Measures; one of thesenbsp;has a length of 81 cm., and a diameter of 27 cm. Specimensnbsp;are not infrequently found with verticils of slender roots innbsp;close proximity to the nodes of the cast; flgures of such rootbearing casts have been given by Bindley and Hutton^ Weisshnbsp;and other authors.

Renault^ has drawn attention to the thinness of the layer of wood which is often associated with large casts of C. Suckowi;nbsp;he concludes that the stems must have possessed little or nonbsp;secondary wood. In a more recent work by Grand�Eury�nbsp;Galamites Suckowi is spoken of as having had wood of thenbsp;Galamodendron type, but a� wood of this kind has not beennbsp;found in England, it is suggested that the plant may not havenbsp;assumed an arborescent habit until late in the Coal-Measurenbsp;period. During the Lower and Middle Coal-Measures, at whichnbsp;horizon it commonly occurs in England, it may have beennbsp;herbaceous. This suggestion has little to commend it; thenbsp;close agreement between G. Suckowi from English and Frenchnbsp;localities points to a plant of the same form, and we have nonbsp;satisfactory evidence as to any difference in stem-structure innbsp;the two cases.

Stur has figured a specimen of a Calamite cast, which he compares with G. Suckowi, surrounded by a band of silicifiednbsp;wood apparently of the Arthropitys type. From this and othernbsp;facts it would appear probable that some of the English stemsnbsp;with the A rthropitys structure possessed casts referable to Galamites (Stylocalamites) Suckowi.

strobili of C. Suckowi, but Stur adduces evidence in support of a connection between this species of Calamite and certainnbsp;Asterophyllitean branches {Galamocladus equisetiformis) bearing Calamostachyan cones. He does not ajDpear to have foundnbsp;the foliage-shoots and stems in organic contact, but drawsnbsp;this conclusion from the association of the fertile branches andnbsp;stems in the same rocks�. This species is abundant in thenbsp;Lower, Middle and Upper Coal-Measures; it has also beennbsp;recorded from the Millstone Grit I

In this sub-genus branch-scars occur on every node; the scars never form a contiguous whorl as in Calamitina, butnbsp;there may be from 3 to 10 on each node. The scars ofnbsp;successive nodes often alternate in position, and thus formnbsp;more or less regular vertical series as shown in fig. 102.nbsp;The most obvious feature as regards the arrangement of thenbsp;branch-scars is their spiral disposition on the surface of thenbsp;pith-cast. The internodes are fairly uniform in length, andnbsp;there is no periodic recurrence of narrower internodes as innbsp;Calamitina. From an examination of specimens of Eucalamitesnbsp;in which the pith-cast is covered with a coaly layer representingnbsp;the carbonised remains of the wood and cortex, it would appearnbsp;that the surface of the stems was practically smooth. Thenbsp;coal}' investment on Eucalamites casts varies considerably innbsp;thickness�; it is very unsafe to make use of the thickness ofnbsp;this layer as a test of the breadth of the wood in Calamiteannbsp;stems. The branch-scars as seen in a surface-view of a stemnbsp;are situated a little above the nodal lines, while depressions onnbsp;the pith-casts occur in the slight nodal constriction or immediately above it. Small leaf-scars have been described as occurringnbsp;on the nodes between the branch-scars in specimens showing thenbsp;surface features^

The species long known as Catamites cruciatugt;s Sternb. is usually taken as the type of the sub-genus Eucalamites.

Weiss' has subdivided this species into several � forms,� which he bases on the number of branch-scars on each node and on othernbsp;characters; a more extended subdivision of G. cruciahts has

.a5 u.'.i*

� '1

recently been made by Sterzelb who admits the impossibility of separating the specific forms by means of the data at ournbsp;disposal, but for purposes of geological correlation he prefersnbsp;to express slight differences by means of definite � forms � ornbsp;varieties. The more comprehensive use of the specific namenbsp;cruciatus as adopted by Zeiller in his Flore de Valenciennes � is,nbsp;I believe, the better method to adopt. The specimen shown innbsp;fig. 102 affords a good example of a typical Calamites cruciatus,nbsp;it was found in the Middle Coal-Measures near Barnsley,nbsp;Yorkshire.

1831. nbsp;nbsp;nbsp;Calamitesnbsp;nbsp;nbsp;nbsp;alternans, Germar andnbsp;nbsp;nbsp;nbsp;Kaulfuss�.

1837. nbsp;nbsp;nbsp;Calamitesnbsp;nbsp;nbsp;nbsp;approximatus, Lindleynbsp;nbsp;nbsp;nbsp;andnbsp;nbsp;nbsp;nbsp;Hutton�.

1884. nbsp;nbsp;nbsp;�nbsp;nbsp;nbsp;nbsp;�nbsp;nbsp;nbsp;nbsp;�nbsp;nbsp;nbsp;nbsp;quaternarius, Weiss�.

1884. nbsp;nbsp;nbsp;�nbsp;nbsp;nbsp;nbsp;�nbsp;nbsp;nbsp;nbsp;�nbsp;nbsp;nbsp;nbsp;genarius, Weiss�.

1884. nbsp;nbsp;nbsp;�nbsp;nbsp;nbsp;nbsp;�nbsp;nbsp;nbsp;nbsp;imdtiramis, Weiss�.

This species occurs in the Upper, Middle and Lower Coal-Measures�. The casts of the cruciatus type have been found associated with wood possessing the structural features of thenbsp;sub-genus Calamodendron^^, but our knowledge of the structurenbsp;of the stem, and of the fertile branches of C. cruciatus is verynbsp;imperfect. A restoration of Calamites {Eucalamites) cruciatusnbsp;is given by Stur� in his classic work on the Calamites, butnbsp;he does not make quite clear the supposed connection with

� Sternberg (25), PI. xlix. fig. 5. nbsp;nbsp;nbsp;�* Brongniart (28�), p. 128, PI. xix.

� Lindley and Hutton (31), PI. ocxvi. nbsp;nbsp;nbsp;quot; Grand�Eury (77), p. 293.

u Kidston (94), p, 249. nbsp;nbsp;nbsp;Grand�Eury (90), p. 216 (expl. plates).

the stems and the fertile shoots of the Asterophyllites t3^pe^ which he describes. Another member of the Eucalamites group,nbsp;which is better known as regards its foliage-shoots, is Galamitesnbsp;ramosus, a species first described by Artis^ in 1825. Stems ofnbsp;this species have been found in connection with the branchesnbsp;and leaves of the Annidariaquot; type, bearing Galamostachys^ cones.nbsp;In all probability pith-casts included in the sub-genus Eucala-mites belonged to stems with foliage-shoots and probably alsonbsp;with cones of more than one form.

In the above account of a few common pith-casts it has been pointed out that there is occasionally satisfactory evidencenbsp;for connecting certain casts with wood of a particular structure,nbsp;and with sterile and fertile foliage-shoots of a definite type. Itnbsp;is, however, impossible in many cases to recognise with anynbsp;certainty the leaf-bearing branches and strobili of the differentnbsp;casts of Galamites; it is equally impossible to determine whatnbsp;type of pith-cast or what type of foliage-shoots belongs tonbsp;petrified stem-fragments in which it is possible to investigatenbsp;the microscopical features. Jhe scattered and piece-mealnbsp;nature of the material on which our general knowledge ofnbsp;Calamitean plants is based, necessitates a system of nomenclature which is artificial and clumsy; but the apparentnbsp;absurdity of attaching different names to fragments, which wenbsp;believe to be portions of the same genus, is of conveniencenbsp;from the point of view of the geologist and the systematist.nbsp;As our material increases it will be possible to further simplifynbsp;the nomenclature for Calamarian plants, but it is unwdse tonbsp;allow our desire for a simpler terminology to lead us intonbsp;proposals which are based rather on suppositions than onnbsp;established fact. If it were possible to discriminate betweennbsp;pith-casts of stems having the different anatomical charactersnbsp;designated by the three sub-genera, ArtAropffys, Arthrodendronnbsp;and Galamodendron, the genus Galamites might be used in anbsp;much narrower and probably more natural sense than thatnbsp;which we have adopted. The tests made use of by some

authors for separating pith-casts of Galamodendron and Ar-thropitys steins do not appear to be satisfactory; we want some term to apply to all Calainitean casts irrespective of the anatomical features of the stems, or of the precise nature of the foliage-branches. As used in the present chapter, Galamites standsnbsp;for plants differing in certain features but possessing commonnbsp;structural characters, which must be defined in a broad sense sonbsp;as to include types which may be worthy of generic rank, butnbsp;which for convenience sake are included in a comprehensivenbsp;generic name. The attempts to associate certain forms of foliagenbsp;with Arthropitys on the one hand and with Galamodendronnbsp;on the other, cannot be said to be entirely satisfactory; we stillnbsp;lack data for a trustworthy diagnosis of distinct Calamariannbsp;genera which shall include external characters as well asnbsp;histological features. If we restricted the genus Galamites tonbsp;stems with an Arthropitys structure and an Asterophylliteannbsp;foliage, we should be driven into unavoidable error. Withinnbsp;certain limits it is possible to distinguish generically or evennbsp;specifically between petrified branches, and we already possessnbsp;material enough for fairly complete diagnoses founded onnbsp;internal structure; but it is not possible to make a parallelnbsp;classification for pith-casts and foliage-shoots. For this reason,nbsp;and especially bearing in mind the importance of namingnbsp;isolated foliage-shoots and stem-casts for geological purposes, Inbsp;believe it is better to admit the artificially wide application ofnbsp;the name Calarnites, and to express more accurate knowledge,nbsp;where possible, by the addition of a subgeneric term. Innbsp;dealing with distinctions exhibited by Calamitean stems it maynbsp;be advisable to make use of specific names, but we must keepnbsp;before us the probability of the pith-cast and petrified stem-fragment of the same plant receiving different specific names.nbsp;If the structural type is designated by a special sub-genus, thisnbsp;will tend to minimise the anomaly of using more than onenbsp;binominal designation for what may be the same individual.

The following summary may serve to bring together the different generic and subgeneric terms which have been usednbsp;in the foregoing account of Galamites.

IV. Conclusion.

A brief sketch of the main features of Calamites suffices to bring out the many points of agreement between the arborescentnbsp;Calamite plants and the recent Equisetums. The slight variation in morphological character among the present-day Horsetails, contrasts with the greater range as regards structuralnbsp;features among the types included in Calamites. The Horsetails probably represent one of several lines of developmentnbsp;which tend to converge in the Palaeozoic period; the Calamitenbsp;itself would appear to mark the culminating point of a certainnbsp;phylum of which we have one degenerate but closely alliednbsp;descendant in the genus Equisetum. We shall, however, be innbsp;a better position to consider the general question of plant-evolution after we have made ourselves familiar with othernbsp;types of Palaeozoic plants. Grand�Eury�s^ striking descriptionsnbsp;1 Grand�Eury (77), (90).

of forests of Calamites in the Coal-Measures of central France, enable us to form some idea of the habit of growth of thesenbsp;plants with their stout branching rhizomes and erect aerialnbsp;shoots.

By piecing together the evidence derived from different sources we may form some idea of the appearance of a livingnbsp;Calamite. A stout branching rhizome ascended obliquelynbsp;or spread horizontally through sand or clay, with numerousnbsp;whorls or tufts of roots penetrating into swampy soil. Fromnbsp;the underground rhizome strong erect branches grew up asnbsp;columnar stems to a height of fifty feet or more; in the lowernbsp;and thicker portions the bark was fissured and somewhatnbsp;rugged, but smoother nearer the summit. Looking up thenbsp;stem we should see old and partially obliterated scars markingnbsp;the position of a ring of lateral branches, and at a higher levelnbsp;tiers of branches given off at regular or gradually decreasingnbsp;intervals, bearing on their upper portions graceful greennbsp;branchlets with whorls of narrow linear leaves. On thenbsp;younger parts of the main shoot rings of long and narrownbsp;leaves were borne at short intervals, several leaf-circles succeeding one another in the intervals between each radiatingnbsp;series of branches. On some of the leaf-bearing branchletsnbsp;long and slender cones would be found here and there takingnbsp;the place of the ordinary leafy twigs. Passing to the apicalnbsp;region of the stem the lateral branches given off at a less andnbsp;less angle would appear more crowded, and at the actualnbsp;tips there would be a crowded succession of leaf-segmentsnbsp;forming a series of overlapping circles of narrow sheaths withnbsp;thin slender teeth bending over the apex of the tree.

Thus we may feebly attempt to picture to ourselves one of the many types of Calamite trees in a Palaeozoic forest, growingnbsp;in a swampy marsh or on gently sloping ground on the shoresnbsp;of an inland sea, into which running water carried its burden ofnbsp;sand and mud, and broken twigs of Calamites and other treesnbsp;which contributed to the Coal Period sediments. The largenbsp;proportions of a Calamite tree are strikingly illustrated bynbsp;some of the broad and long pith-casts occasionally seen innbsp;Museums; in the Breslau Collection there is a cast of a stem

belonging to the sub-genus Galamitina, which measures about 2 m. in length and 23 cm. in breadth, with 36 nodes. In thenbsp;Natural History Museum, Paris, there is a cast nearly 2 metresnbsp;long and more than 20 cm. wide, which is referred to the subgenus Galamodendron.

In the Upper Devonian and Culm rocks casts of a well-defined Calamitean plant are characteristic fossils; stems, leafbearing branches, roots and cones have been described by several authors,' and the genus Archaeocalamites has been institutednbsp;for their reception. Although this genus agrees in certainnbsp;respects with Galamites, and as recent w'Ork has shown thisnbsp;agreement extends to internal structure, it has been thenbsp;custom to regard the Lower Carboniferous and Devonian plantsnbsp;as generically distinct. The surface features of the stem-casts,nbsp;the form of the leaves, and apparently the cones, possess certainnbsp;distinctive characters which would seem to justify the retentionnbsp;of a separate generic designation.

Pith-casts articulated, with very slightly constricted nodes; the internodes traversed by longitudinal ribs slightly elevatednbsp;or almost flat, separated by shallow grooves. The ribs andnbsp;grooves are continuous from one internode to another, and donbsp;not usually show the characteristic alternation of Galamites^.nbsp;Along the nodal line there are occasionally found short longitudinal depressions, probably marking the points of origin ofnbsp;outgoing bundles. Branches were given off from the nodesnbsp;without any regular order; a pith-cast may have branch-scarsnbsp;on many of the nodes, or there may be no trace of branchesnbsp;on casts consisting of several nodes. The leaves� are in whorls;nbsp;in some cases they occur as free, linear, lanceolate leaves, or onnbsp;younger branches they are long, filiform and repeatedly forked.

^ For good figures of the leaves vide Stur (75), Rothpletz (80), Ettings-hausen (66), Solms (96).

The structure of the wood agrees with that of some forms of Arthropitys. The strobili consist of an articulated axis bearingnbsp;whorls of sporangiophores, and each sporangiophore has fournbsp;sporangia. Our knowledge of the fertile shoots is, however,nbsp;very imperfect.

Renault^ has recently described the structure of the wood in some small silicified stems of Archaeocalamites from Autun.nbsp;A large hollow pith is surrounded b}� a cylinder of woodnbsp;consisting of wedge-shaped groups of xylem tracheids associatednbsp;with secondary medullary rays; at the apex of each primarynbsp;xylem group there is a carinal canal. The primary medullarynbsp;rays appear to have been bridged across by bands of xylem atnbsp;an early stage of secondary thickening, ^ as in the Calamitenbsp;of fig. 83,1).

Our knowledge of the cones of Archaeocalamites is far from satisfactory. Renault^ has recently described a small fertilenbsp;branch bearing a succession of verticils of sporangiophores;nbsp;each sporangiophore stands at right angles to the axis ofnbsp;the cone*and bears four sporangia, as in Calamostachys. It isnbsp;not clear how far there is better evidence than that afforded bynbsp;the association of the specimen with pith-casts of stems, fornbsp;referring this cone to Archaeocalamites, but the association ofnbsp;vegetative and fertile shoots certainly suggests an organicnbsp;connection. The cone described by the French author agreesnbsp;with Equisetum in the absence of sterile bracts between thenbsp;whorls of sporangiophores. It is an interesting fact that suchnbsp;a distinctly Equisetaceous strobilus is known to have existednbsp;in Lower Carboniferous rocks.

Stur� has also described Archaeocalamites at considerable length ; he gives several good figures of stem-casts and foliage-shoots bearing long and often forked narrow leaves. The samenbsp;writer describes specimens of imperfectly preserved cones innbsp;which portions of whorls of forked filiform leaves are given off

^ Renault (96), p. 80; (93), Pis. xlii. and xliii. Since the above was written an account of the internal structure of Archaeocalamites has been published bynbsp;Solms-Laubach (97); he describes the wood as being of the Arthropitys type.

from the base of the strobilush Kidston^ published an important memoir on thenbsp;cones of Archaeocalamites in 1883, innbsp;which he advanced good evidence innbsp;support of the view that certain strobili,nbsp;which were originally described asnbsp;Monocotyledonous inflorescences, undernbsp;the generic name Pothocites^, are thenbsp;fertile shoots of this Calamarian genus.nbsp;Kidston�s conclusions are based on thenbsp;occurrence on the Pothocites cones, ofnbsp;leaves like those o� Archaeocalamites,onnbsp;the non-alternation of the sporangio-phores of successive whorls, and on thenbsp;close resemblance between his specimens and those described by Stur.nbsp;Good specimens of the cones, formerlynbsp;known as Pothocites, may be seen innbsp;the Botanical Museum in the Royalnbsp;Gardens, Edinburgh; as they are innbsp;the form of casts without' internalnbsp;structure it is diflScult to form a clearnbsp;conception as to their morphologicalnbsp;features.

The fossils included under Archaeocalamites have been referred by different authors to various genera,nbsp;and considerable confusion has arisennbsp;in both generic and specific nomenclature. The following synonomy ofnbsp;the best known species, A. scrohiculatusnbsp;(Schloth.) illustrates the unfortunatenbsp;use of several terms for the same plant.

^ An examination of the specimens in the Museum of the Austrian Geology Survey did not enable me to satisfactorily verify the features of the cone asnbsp;described by Stur; the impressions are far from clear.

Archaeocalaniites scrobicidatus (Schloth.). Fig. 103.

Lithoxylon, Volkmann'.

Calamites scrohicidatua, Schlotheim^. Bornia scrohiculata, Sternberg^.

Calamites radiatus, Brongniart^.

Pothocites Oranton\ Paterson �.

Calamites transitionis, G�ppert�. Stigmatocanna Volkmanniana, ibid.nbsp;Anarthrooanna tuherculata, ibid.

Calamites variolatus, ibid.

C. ohliquus, ibid.

C. temdssimus, ibid.

Asterophyllites elegans, ibid.

Calamites laticulatiCs, Ettiiigshausen^. �quisetites O�pperti, ibid.

Sphenophyllum furcatum, ibid. Asterophyllites spaniophyllus, FeistmanteP.nbsp;Asterocalamites scrobicidatus, Zeiller'*.

For other lists of synonyms reference may be made to Binney�, Stur�, Kidston'^ and other authors.

Some of the best specimens of this species are to be seen in the Museums of Breslau and Vienna, which contain the originalnbsp;examples described by G�ppert and Stur. An examination ofnbsp;the original specimens, figured by G�ppert under various names,nbsp;enables one to refer them with confidence to the single species,nbsp;Archaeocalamites scrobiculatus. The generic name Archaeo-calamites, which has been employed by some authors, wasnbsp;suggested by Schimper�� in 1862, as a subgenus of Calamites,nbsp;on account of the occurrence of a deeply divided leaf-sheath,nbsp;attached to the node of a pith-cast, which seemed to differ from

2 nbsp;nbsp;nbsp;Schlotheim (20), p. 402, PI. xxii. fig. 4.nbsp;nbsp;nbsp;nbsp;'�gt; Sternberg (25).

� Paterson (41), PI. iii. nbsp;nbsp;nbsp;� G�ppert (52), Pis. iii., v., vi., viii., xxxviii.

�� Ettingshausen (66), Pis. i.�iv. nbsp;nbsp;nbsp;� Feistmantel (73), PI. xiv. fig. 5.

Schimper and Koechlin-Schlumberger (62), PI. i. The original specimens of Schimper�s figures are in the Strassburg Museum.

the usual type of Calamitean leaf. The specimens described by Schimper are in the Strassburg Museum; the leaf-sheathnbsp;which he figures is not very accui�ately represented.

The example given in fig. 103 shews very clearly the continuous course of the ribs and grooves of the pith-cast. Each rib is traversed by a narrow median groove which would seem tonbsp;represent the projecting edge of some hard tissue in the middlenbsp;of each principal medullary ray of the stem. The specimen wasnbsp;found in a Carboniferous limestone quarry, Northumberland;nbsp;there is a similar cast from the same locality in the Museum ofnbsp;the Geological Survey.

This genus agrees very closely with Calamites both in the anatomical structure of the stem and in the verticillate disposition of the leaves. The strobili appear to be Equisetaceous innbsp;character, and there is no satisfactory evidence of the existencenbsp;of whorls of sterile bracts in the cone, such as occur innbsp;Calaniostachys and in other Calamitean strobili. The continuousnbsp;course of the vascular bundles of the stem from one internodenbsp;to the next is the most striking feature in the ordinary specimensnbsp;of the genus; but it sometimes happens that the grooves on anbsp;pith-cast shew the same alternation at the node as in Calamites.nbsp;This is the case in a specimen in the Goppert collection innbsp;the Breslau Museum, and FeistmanteB has called attention tonbsp;such an alternation in specimens from Rothwaltersdorf. In thenbsp;true Calamites, on the other hand, the usual nodal alternationnbsp;of the vascular strands is by no means a constant character^.nbsp;Stur��, Rothpletz'', and other authors have pointed out the resemblance of Archaeocalamites to Sphenophyllum. The deeplynbsp;divided leaves of some Sphenophyllums and those of Archaeocalamites are very similar in form; and the course of thenbsp;vascular strands in SphenophyUiim may be compared with thatnbsp;in Archaeocalamites. But the striking difference in the structure

of the stele forms a wide gap between the two genera. We have evidence that the Calamites and Sphenophyllums werenbsp;probably descended from a common ancestral- stock, and itnbsp;may be that in Archaeocalamites, some of the Sphenophylliminbsp;characters have been retained; but there is no close affinitynbsp;between the two plants.

On the whole, considering the age of Ai'chaeocalamites and the few characters with which we are acquainted, it is probablenbsp;that this genus is very closely related to the typical Calamites,nbsp;and may be regarded as a type which is in the direct line ofnbsp;development of the more modern Calamite and the livingnbsp;Equisetum. Weiss' inchrdes Archo.eocalamites as one of hisnbsp;subgenera with Galamitina and others, and it is quite possiblenbsp;that the genus has not more claim to stand alone than othernbsp;forms at present included in the comprehensive genus Calamites.

The student will find detailed descriptions of this genus in the works which have been referred to in the preceding pages.

CHAPTER XI.

The genus Sphenophyllum is placed in a special class, as representing a type which cannot be legitimately included innbsp;any of the existing groups of Vascular Cryptogams. Althoughnbsp;this Palaeozoic genus possesses points of contact with variousnbsp;living plants, it is generally admitted by palaeobotanists that itnbsp;constitutes a somewhat isolated type among the Pteridophytesnbsp;of the Coal-Measures. Our knowledge of the anatomy of bothnbsp;vegetative shoots and strobili is now fairly complete, and thenbsp;facts that we possess are in favour of excluding the genus fromnbsp;any of the three main divisions of the Pteridophyta.

In Scheuchzer�s Herbarium Diluvianum there is a careful drawing of some fragments of slender twigs, from an Englishnbsp;locality, bearing verticils of cuneiform leaves, which the authornbsp;compares with the common Galium^. As regards superficialnbsp;external resemblance, the Galium of our hedgerows agrees verynbsp;closely with what must have been the appearance of fresh greennbsp;shoots of Sphenophyllum.

A twig of the same species of Sphenophyllum is figured by Schlotheim^ in the first part of his work on fossil plants; henbsp;regards it as probably a fragment of some species of Palm.nbsp;Sternberg� was the first to institute a generic name for thisnbsp;genus of plants, and specimens were described by him in 1825

Scheuchzer (1723), p. 19, PI. iv. fig. 1. Sehlotheim (04), Pi. ii. fig. 24, p. 57.

as a species of the genus Rotularia. The name SphenopJiyllites was proposed by Brongniart* in 1822 as a substitute fornbsp;Schlotheim�s genus, and in a later work^ the French authornbsp;instituted the genus Sphenophylliim. Dawson� was the first tonbsp;make any reference to the anatomy of this genus ; but it is fromnbsp;the examination of the much more perfect material fromnbsp;St. Etienne, Autun, and other continental localities, the Northnbsp;of England and Pettycur in Scotland, by Renault, Williamson,nbsp;Zeiller and Scott, that our more complete knowledge has beennbsp;acquired.

The affinity of Sphenophylluni has always been a matter of speculation; it has been compared with Dicotyledons, Palms,nbsp;Conifers (Ginkgo and Phyllocladus), and various Pteridophytes,nbsp;such as Ophioglossum, T7nesipteris, Marsilia, Salvinia, Equisetumnbsp;and the Lycopodiaceae'*.

Stem comparatively slender (1'.5�15 mm.?), articulated, usually somewhat tumid at the nodes; the surface of thenbsp;internodes is marked by more or less distinct ribs and groovesnbsp;which do not alternate at the nodes, but follow a straight coursenbsp;from one internode to the next. A single branch is occasionallynbsp;given off from a node. Adventitious roots are very rarely seen,nbsp;their surface does not show the ridges and grooves of the foliage-shoots.

The leaves are borne in verticils at the nodes, those in the same whorl being usually of the same size, but in some formsnbsp;two of the leaves are distinctly smaller than the others. Eachnbsp;verticil contains normally 6, 9, 12, 18 or more leaves, which arenbsp;separate to the base and not fused into a sheath; the numbernbsp;of leaves in a verticil is not always a multiple of six. They varj-in form from cuneiform with a narrow tapered base, and a laminanbsp;traversed by several forked veins, to narrow uninerved leavesnbsp;and leaves with a lamina dissected into dichotomously branched

* For reference vide an excellent monograph by Coemans and Kickx (64), also Potoni� (94).

The strobili are long and narrow in form, having a length in some cases of 12 cm., and a diameter of 12 mm.; they occur asnbsp;shortly stalked lateral branches, or terminate long leaf-bearingnbsp;shoots. The axis of the cone bears whorls of numerous linearnbsp;lanceolate bracts fused basally into a coherent funnel-shapednbsp;disc, bearing on its upper surface sporangiophores and sporangia.

The stem is monostelic, with a triarch or hexarch triangular strand of centripetally developed primary xylem, consisting ofnbsp;reticulate, scalariform and spiral tracheae; the protoxylemnbsp;elements being situated at the blunt corners of the xylem-strand. Foliar bundles are given off, either singly or in pairs,nbsp;from each angle of the central primary strand. The secondarynbsp;xylem consists of radially disposed reticulate or scalariformnbsp;tracheae, developed from a cambium-layer. The phloem isnbsp;made up of thin-walled elements, including sieve-tubes andnbsp;parenchyma. Both xylem and phloem include secondarynbsp;medullary rays of parenchymatous cells. The cortex consistsnbsp;in part of fairly thick-walled elements; in older stems thenbsp;greater part of the cortical region is cut off by the developmentnbsp;of deep-seated layers of periderm.

The branch of Sphenophyllum emarginatum Brongn. given in fig. 109 shows the characteristic appearance of the genus asnbsp;represented by this well-known species which Brongniartnbsp;figured in 1822. The Indian species shown in fig. Ill illustrates the occurrence of unequal leaves in the same whorl, andnbsp;in fig. 110, B, we have a form of verticil in which the leavesnbsp;are deeply divided into filiform segments. A larger-leavednbsp;form is represented by S. Thoni, Mahr. (fig. 110, A), a speciesnbsp;occasionally met with in Permian rocks.

No specimens of Sphenophyllum have so far been found attached to a thick stem; they always occur as slender shoots,

which sometimes reach a considerable length. One of the longest examples known is in the collection of the Austriannbsp;Geological Survey; the axis is 4 mm. in breadth and 85 cm.nbsp;long, bearing a slender branch 61 cm. in length. Thenbsp;manner of occurrence of the specimen as a curved slendei-stem on the surface of the rock suggests a weak plant, whichnbsp;must have depended for support on some external aid, eithernbsp;water or another plant. The anatomical structure and othernbsp;features do not favour the suggestion of some writers thatnbsp;Sphenophyllum was a water-plant^ but there would seem tonbsp;be no serious obstacle in the way of regarding it as possibly anbsp;slender plant which flung itself on the branches and stems ofnbsp;stronger forest trees for support.

The following account of the structural features of the stem and root is based on tbe work of Eenault�, Williamson^ andnbsp;Williamson and Scott^. We may first consider such charactersnbsp;as have been recognised in different examples of the genus, andnbsp;then notice briefly the distinguishing peculiarities of two well-marked specific types.

In a transverse section of a young Sphenophyllum stem such as that diagrammatically sketched in fig. 105, A, we find in thenbsp;centre the xylem portion of a single stele with a characteristicnbsp;triangular form. The primary xylem consists mainly of fairlynbsp;large tracheae with numerous pits on their walls; towards thenbsp;end of each arm the tracheids become scalariform, and at thenbsp;apex there is a group of narrower spiral protoxylem elements.nbsp;In the British species there is a single protoxylem group at thenbsp;apex of each arm, but Renault has described some Frenchnbsp;stems in which the stele appears to be hexarch, having two protoxylem groups at the end of each of the three rays of the stele.nbsp;The primary xylem strand of Sphenophyllum has therefore a

root-like structure, the tracheids having been developed centri-petally from the three initial protoxylem groups. This type of structure is typical of roots, but it also occurs in the stems ofnbsp;some recent Vascular Cryptogams.

As a rule the tissue next the xylem has not been petrified, but in exceptionally well-preserved examples it is seen tonbsp;consist of a band of thin-walled elements, of which those innbsp;contact with the xylem may be spoken of as phloem, and thosenbsp;beyond as the pericycle. Succeeding this band of delicatenbsp;tissue there is a broader band of thicker-walled and somewhatnbsp;elongated elements, constituting the cortex. The specimennbsp;drawn in fig. 105, A, shows very prominent grooves in the cortexnbsp;opposite the middle of each bay of the primary wood. It isnbsp;these grooves that give to the ordinary casts of Sphenophyllumnbsp;branches the appearance of longitudinal lines traversing eachnbsp;internode. In a longitudinal section of a stem, the corticalnbsp;tissue (fig. 104, c) is found to be broader in the nodal regions.

c, outer cortex; b, space next the stele, originally occupied by phloem etc.-, a, xylem strand. (After Eenault^.) x 7.

* Specimen 929 in the Williamson Cabinet is a longitudinal section of the French Sphenophyllum, as described by Benault (76^).

thus giving rise to the tumid nodes referred to in the diagnosis. The increased breadth at the nodes does not meannbsp;that the xylem is broader in these regions, as it is in Calamitenbsp;stems. Small strands of vascular tissue are given off from thenbsp;three edges of the triangular stele (fig. 105^4) at each node;

these branch in passing through the cortex on their way to the verticils of leaves. The space h in the diagrammaticnbsp;section of fig. 104 was originally occupied by the phloem andnbsp;inner cortex. In some species of Sphenophyllum the apex ofnbsp;each arm of the xylem strand, as seen in transverse section, isnbsp;occupied by a longitudinal canal surrounded by spiral tracheids,nbsp;as in the primary xylem of the old stem showm in fig. 105, C.

With the exception of very young twigs the petrified Sphem-phyllum stems usually show a greater or less development of secondary wood. In the xylem-strand of fig. 105, B, the broadnbsp;concave bays of the primary wood have been filled in by thenbsp;development of two rows of large secondary tracheids, x, butnbsp;opposite the protoxylem groups, px, there are no signs ofnbsp;cambial activity. In the unusually large stem represented bynbsp;a rough sketch in fig. 105, G, the triangular primary xylemnbsp;lies in the centre of a thick mass of secondary vascular tissue.nbsp;The secondary and primary wood together have a diameter ofnbsp;about 5 mm.

After the bays between each protoxylem corner have been filled in, the formation of secondary wood proceeds uniformlynbsp;along the stem radii, but the rows of tracheids and medullarynbsp;rays which are developed opposite the corners of the primarynbsp;strand, c, differ in certain characters from the broader massesnbsp;of wood opposite the bays. For convenience, the secondarynbsp;wood, c, opposite the protoxylem groups has been spoken of asnbsp;fascicular wood, and the rest, d, as interfascicular wood.

The secondary xylem consists either of tracheae with numerous bordered pits on their radial walls (fig. 105, D), or ofnbsp;tracheae wdth broad and bordered scalariforrn pits (fig. 105, E).nbsp;The suggestion of concentric rings of growth in the wood innbsp;fig. 105, C, is rather deceptive ; there are no well-marked regularnbsp;rings in Sphenophyllum stems, but irregular bands of smallernbsp;elements occasionally interrupt the uniformity of the secondarynbsp;xylem. In some sterns the medullary rays have the form ofnbsp;rows of parenchymatous cells, which in tangential longitudinal

section are found to consist frequently of a single row of radially disposed elements; this type of medullary rays occurs in thenbsp;species Sphenophyllum msigne, in which the tracheae are scalari-form. Three medullary rays, r, are seen on the radial face ofnbsp;the scalariform tracheids in fig. 105, E, which represents a radialnbsp;section of this species. In other species, e.g. S. pluri/oliatum, thenbsp;medullary rays have a peculiar and characteristic structure; innbsp;a transverse section of the stem they appear as groups of anbsp;few parenchymatous cells in the spaces between the truncatednbsp;angles of the large tracheae (fig. 100). In longitudinal sectionnbsp;these medullary-ray elements resemble thick bars stretchingnbsp;radially across the face of the tracheae (fig. 105, D, r); thenbsp;apparent septa or bars are however thin-walled cells connectingnbsp;the different groups of medullary-ray cells, as seen in a transversenbsp;section. These radial connecting cells are occasionally seen asnbsp;short rays in transverse sections of stems.

The cambium and phloem elements are occasionally preserved in good specimens of older stems; the former consist of tabular flatted thin-walled cells, and the latter in some casesnbsp;include large sieve-tubes and narrower parenchymatous elements.

The sections shown in fig. 107, E and F, illustrate the preservation of cambial and phloem tissue. In the transversenbsp;section of fig. 107, F, the secondary xylem with the medullar}^nbsp;rays, r, is succeeded by a few tabular cambium cells, and externalnbsp;to these there are thin-walled elements of unequal size representing the phloem. In fig. 107, E, the scalariform tracheidsnbsp;are succeeded by narrow thin-walled cells, and the largernbsp;elements with transverse and oblique septa are no doubtnbsp;sieve-tubes.

In the large stem of fig. 105, 0, the xylem is succeeded by a band of tissue, a, which is no doubt phloem, and external tonbsp;this there is a considerable development of periderm (b). Thenbsp;periderm in Sphenophyllum stems had a deep-seated origin,nbsp;the phellogen or cork-cambium occasionally being formed innbsp;the secondary phloem-parenchyma, and in other cases in thenbsp;pericycle, as in the stems of some living dicotyledons. Williamson and Scott' describe stems in which a succession of phellogensnbsp;' Williamson and Scott (94), p. 926.

were formed at different levels, thus producing a scaly type of bark, such as we find in the Pine or the Plane tree.

Before describing the structure of the strobili of Spheno-phyllum, we may briefly point out the distinguishing features of two specific types of the genus recently described by Williamsonnbsp;and Scott. One of these species, S. insigne, was originallynbsp;described by Williamson as an Asterophyllites; the numerousnbsp;narrow linear leaves in each verticil led to the inclusion of thenbsp;specimens in the latter genus. The material on which thisnbsp;species is founded is from the volcanic beds of Pettycur,nbsp;Burntisland, on the coast of the Firth of Forth.

An intercellular space occurs at each angle of the three-rayed primary xylem strand, and spiral tracheae are abundant. The tracheae of the secondary wood have scalariform markingsnbsp;on the radial walls. Regular medullary rays extend throughnbsp;the secondary wood. The phloem contains large sieve-tubes.

This species occurs in the Calciferous sandstone rocks of Burntisland, and has lately been recorded from Germany. Itnbsp;characterises a lower horizon than S. plunfoliatum (Will, andnbsp;Scott).

The specific name plurifoliatum was proposed by Williamson and Scott for a type of stem originally described by Williamson�*nbsp;as an Asterophyllites, from the Coal-Measures of Oldham, Lancashire. This form of stem has not so far been connectednbsp;with any of the older species founded on external characters,

but it evidently bore foliage in which the leaves were deeply divided, as in Sphenophyllum trichornatosum (fig. 110, B).

In this species there are no canals at the angles of the primary xylem, and there are fewer spiral tracheae than innbsp;8. insigne. The tracheae of the secondary wood have numerousnbsp;.small pits on the radial walls, and the medullary rays arenbsp;chiefly composed of parenchymatous cells, which appear innbsp;transverse section as groups of cells between the truncatednbsp;angles of the tracheae. The characters are fairly well seen innbsp;the xylem portion of a stele shown in fig. 106. The fiiscicularnbsp;wood includes some rows of parenchymatous medullary-raynbsp;cells in addition to the characteristic groups, as seen in thenbsp;figure. A slightly oblique transverse section of a stem is oftennbsp;convenient in the interpretation of histological features; one ofnbsp;the sections of 8. plurifoUatum in the Williamson collectionnbsp;(no. 893), which has been cut somewhat obliquely, shows verynbsp;clearly the differences in pitting exhibited by the differentnbsp;xylem elements.

Our knowledge of the anatomy of Sphenophyllimi roots is very limited. Renault has described a somewhat' imperfectnbsp;example of a silicified root from St. Etienne and Autun. Thenbsp;drawing in fig. 107, B, which is copied from one of Renault�snbsp;figures, shows a cylindrical mass of xylem with a small band ofnbsp;narrower elements occupying the centre, and surrounded by'nbsp;rows of larger secondary tracheae. The central bipolar bandnbsp;is described as the diarch primary xylem, around which thenbsp;secondary pitted elements have been developed.

It is probable that the specimen described by Renault is a root of Sphenophyllum, but my irnpr�ssion gained frofn afinbsp;examination of the section was that the diarch primary strandnbsp;is not quite so clear as in the published figures. Until wenbsp;possess better material we cannot attempt any very satisfactorynbsp;description of the anatomical features of the roots of, thisnbsp;genus.

A section of a Sphenophyllum stem has been figured by Felix', in which a lateral member is being given off; this maynbsp;possibly represent the origin of an adventitious root, but thenbsp;preservation is not sufficiently distinct to render this certain.

Renault^ has described some silicified leaves of Sphenophyllum from Autun in which the laminae consist of thin-walled loose parenchyma, traversed by small groups of tracheids constituting the simple or forked veins. The epidermis is made upnbsp;of a single layer of cells, with here and there indistinct indications of stomata. A rnore perfect stoma has, however, beennbsp;described by Solms-Laubach from the epidermis of a bract in anbsp;strobilus (fig. 107, A).

Fig. 107. A. Stoma in a bract of Spheno�phyllostachys. B. Root of Sphenophylhim. C. Sphenophyllostachys ��meri, � Solms. s, sporangiophore, b, bract. D. Sporangium. E and F. Sections through the cambium, phloem andnbsp;secondary xylem of Sphenophyllum insigne (Will,), s, sieve-tube. G. Sporangium and pedicel. A, C, D. Afternbsp;Solms-Laubach. B. After Renault. E�G, After Williamson and Scott. E. F. x 100. G. x 115.

The hist�iy of the recognition of the cones of Sphenophyllum has already been briefly alluded to in chapter V., p. 100. Thenbsp;main points in the structure of the cones of this genus werenbsp;known for several years, before the fact was established thatnbsp;they belonged to Sphenophyllum stems. In 1871 Williamson^nbsp;published an account of an imperfect fossil strobilus from thenbsp;Lower Coal-Measures of Oldham, Lancashire, under the name ofnbsp;Volkmannia Dawso7ii. The generic term Volkmamiia has beennbsp;used by different writers for cones varying considerably innbsp;structural features; in the case of Williamson�s fossil, Weiss'�nbsp;substituted the name Bowmanites, a genus instituted by Binney�nbsp;for a strobilus apparently of the same type as Volhnannianbsp;Dawsoni. In 1891 Williamson^ described some additional specimens of Bowmayiites Dawsoni, and, as in his earlier paper, henbsp;compared the strobilus with Asterophyllites and Sphenophyllum,nbsp;but it was still a matter of speculation as to what was the formnbsp;of the vegetative branches. Soon after the more completenbsp;account of the English cones was published, Zeiller� recognisednbsp;a close agreement between some French and Belgian specimensnbsp;of Sphenophyllum strobili and the strobilus described by Williamson. A closer comparison thoroughly established the connectionnbsp;between Bowmanites Dawsoni and Sphenophyllum; and there isnbsp;little doubt that this strobilus belongs to the stem known asnbsp;Sphenophyllum cuneifolium (Sternb.)�a well-known species ofnbsp;the genus.

The most important morphological features of the strobilus of Sphenophyllum may best be illustrated by a detailed accountnbsp;of one specific type, and by a brief reference to other forms whichnbsp;are characterised by certain differences in the number and attachment of the sporangia. When we know that a given strobilusnbsp;must have grown on a Splteyiophyllum stem, the obvious namenbsp;to assign to it would seem to be that of the plant which bore it;nbsp;but there are advantages in making use of special generic termsnbsp;for detached cones, which cannot be referred with certainty to a

1 Williamson (71^). nbsp;nbsp;nbsp;Weiss (84), p. 200.nbsp;nbsp;nbsp;nbsp;� Binney (71).

particular species of stem. The genus Calamostachys affords an example of a name which is intended to denote that a conenbsp;so called belongs to a Calamarian plant; similarly such a namenbsp;as Sphenophyllostachys may he used for Sphenophylloid conesnbsp;which cannot be connected with certainty to particular speciesnbsp;of Sphenophyllum. It has been suggested that the genusnbsp;Bowmanites, first used for a cone which was afterwards recognised as belonging to a Sphenophyllum, should be employednbsp;instead of the sesquipedalian term Sphenophyllostachys. Thenbsp;latter is used here as being in accordance with a generall}'nbsp;accepted and convenient system of nomenclature, and as anbsp;name which at once denotes the fact that the fossil is not onlj-a cone but that it belongs to a Sphenophyllum.

The cone consists of a central axis bearing a number of verticils of bracts coherent in their lower portions in the form

of a widely open funnel-shaped disc, which splits up peripherally into 14�20 linear-lanceolate segments. The free segments ofnbsp;each verticil have an obliquely ascending or almost vertical position, and extend upwards for a distance of about six internodes.nbsp;The smaller drawing in fig. 108 shows the appearance in sidenbsp;view of the narrow bracts of a single whorl. A transversenbsp;section of a strobilus would include, therefore,, sections ofnbsp;several concentric series of ascending bracts. The verticils ofnbsp;Sphenophyllostachys Dawsoni are probably superposed, but thisnbsp;point has not been definitely settled. From the upper surfacenbsp;of the coherent basal portion of each verticil, there are given offnbsp;twice as many sporangiophores as there are free segments, andnbsp;these are attached close to the line of junction of the axis of thenbsp;cone and the funnel-shaped disc. Each sporangiophore has thenbsp;fotm of a slender stalk which bends inwards at its distal endnbsp;and bears a single sporangium {cf. fig. 107, D). The sporangiophores given off from the same verticil of bracts vary in length.nbsp;All the sporangiophores are attached to the coherent bracts atnbsp;the same distance from the axis of the cone ; but as the sporangianbsp;between each verticil of bracts are arranged in two or threenbsp;concentric series, it follows that the length of the sporangiophores varies considerably. The diagrammatic longitudinalnbsp;section of a strobilus in fig. 108 shows three concentric seriesnbsp;of sporangia between successive bract-verticils. A similarnbsp;diagram was published by Williamson in 1892', and afterwards copied by Potoni�^ but in Williamson�s restoration thenbsp;sporangiophores of the three series of sporangia are erroneouslynbsp;represented as arising from different points on the surface ofnbsp;the bracts. There is little doubt, as regards the strobilus of S.nbsp;cuneifoliwm, that the sporangiophores were given off in a singlenbsp;series close to the axils of the bracts, as is partially shown innbsp;fig. 108.

The central part of the axis of the cone is occupied by a single triangular stele like that of the stem, except that eachnbsp;ray of the xylem strand has a comparatively broad bluntnbsp;termination, and is not tapered to a narrow arm as in fig. 105,

A and B. The wood consists of pitted tracheae, with two groups of protoxylem elements at each of the truncated angles of thenbsp;solid strand of xylem. From the angles of the stele branchesnbsp;of vascular tissue pass out through the cortex to supply thenbsp;sterile and fertile segments of each verticil. One of thenbsp;transverse sections of the Sphmophyllum cone in the Britishnbsp;Museum Collection (no. 1898 E) affords a good example of thenbsp;misleading appearance occasionally presented by an intrudednbsp;� rootlet � of Stigmaria; the vascular tissue of the cone hasnbsp;disappeared, and a Stigmarian appendage with its vascularnbsp;bundle occupies the position of the stelar tis.sues.

The bracts consist of parenchymatous tissue limited externally by an epidermis containing stomata. A single stoma with subsidiary cells is represented in fig. 107, A. Thenbsp;sporangiophores are composed internally of thin-walled cellsnbsp;with stronger cells tow'ards the surface. The longer sporangiophores in a series may be more or less coherent for part ofnbsp;their length to the upper surface of the verticil of bracts. Innbsp;fig. 108 the slender sporangiophores do not appear to comenbsp;off always from the same portion of the bracts, but this is duenbsp;to some of them lying on the surface of the latter during partnbsp;of their course to support the external circle of sporangia.nbsp;The hook-like distal end of a sporangiophore, towards the pointnbsp;of attachment of the sporangium, is characterised by the largernbsp;size and greater prominence of the surface cells; these largernbsp;cells, which pass over the upper surface of a sporangium base,nbsp;probably constitute a kind of annulus which determines thenbsp;dehiscence of the sporangial walk.

Fig. 107, (t, represents a sporangiophore and its sporangium cut through transversely just below the point of attachment ofnbsp;the latter to the end of the hook-like termination of the former.nbsp;The spores are characterised by an irregularly reticulatenbsp;thickening of the outer coat or exospore, as seen in the figure.

One of the chief points of interest suggested by a Spheno-phyllum cone is the exact morphological nature of the sporangiophores. Are they branches borne in the axils of bracts, or

^ For a more complete account of this strobilus vide Zeiller (93), and Williamson (91^), etc.

may we regard each sporangiophore as a modified leaf, which has become coherent with the whorls of sterile leaves ? Or isnbsp;a sporangiophore merely a stalk of a sporangium ; or a ventralnbsp;lobe of a leaf, of which the sterile bracts represent the dorsalnbsp;lobes ? Although it is impossible without the evidence ofnbsp;development to decide with certainty between these alternatives, it would seem most probable that a sporangiophorenbsp;may be looked upon as a ventral lobe of a leaf, the sterile lobesnbsp;forming the bracts or members of the sterile whorls of thenbsp;cone. This question is discussed by Zeiller* and Williamsonnbsp;and Scotty also more recently by Scott^ in his memoir onnbsp;Cheirostrobus.

In another type of Sphenophyllum strobilus, recently described by Solms-Laubach, the incurved end of each sporangiophore bore two sporangia. In most respects this species,nbsp;which has not been found in connection with a vegetativenbsp;shoot, agrees with Sphenophyllostachys Dawsoni.

In fig. 107, C, which is copied from one of Solms-Laubach�s drawings�, we have an oblique transverse section of part of anbsp;strobilus, including portions of two series of sporangia borne onnbsp;one verticil of bracts, and at the right-hand edge the sectionnbsp;has passed through the sporangia belonging to another whorlnbsp;of bracts. There were probably three concentric series ofnbsp;sporangia attached to each verticil of bracts, as in the case ofnbsp;fig. 108. The unshaded area, b (fig. 107, C), represents the bractsnbsp;of two successive sterile whorls in transverse section. The shadednbsp;areas are the sporangia, with their sporangiophores, s. Thenbsp;relative position of the sporangia and sporangiophores suggestsnbsp;that each pedicil bore tw'o sporangia at its tip, instead of one,nbsp;as in the strobilus of Sphenophyllum cuneifolimn (Sternb.).

A further variation in the structure of the strobili is illustrated by some specimens of S. trichomatosuni Stur,nbsp;described by Kidston\ from the Coal-Measures of Barnsley.nbsp;Each whorl of bracts hears a single series of oval sporangianbsp;which appear to be sessile on the basal portion of the whorl.nbsp;It is possible that delicate sporangiophores may have beennbsp;present, but in the imperfect examples in Kidston�s collection^nbsp;the sporangia present the appearance of being seated directlynbsp;on the surface of the bracts. As the specimens do not shownbsp;any , internal structure, it would be unwise to lay too muchnbsp;stress on the apparent absence of the characteristic sporangiophores. In any case, Kidston�s cones afford an illustration ofnbsp;the occurrence of a single series of sporangia in each whorl,nbsp;instead of the pluriseriate manner of occurrence in some othernbsp;species.

The statement is occasionally met with that some Spheno-phyllum cones possessed two kinds of spores, but we are still in want of satisfactory evidence that this was really the case.nbsp;Renault has described an imperfect specimen, which he considers points to the heterosporous nature of a Sphenophyllumnbsp;cone, but Zeiller and Williamson and Scott have expressednbsp;doubts as to the correctness of Renault�s conclusions. Whilenbsp;admitting the possibility of undoubted heterosporous strobilinbsp;being discovered, we are not in a position to refer to Sphenophyllum as having borne strobili containing two kinds ofnbsp;spores�.

[The following are some of the specimens in the Williamson Cabinet which illustrate the structure of Sphenophyllum :�

S. plurifoliaUm. nbsp;nbsp;nbsp;874, 882, 884, 893, 894, 897, 899, 901, 903, 908, 1893.

� I am indebted to my friend Mr Kidston for an opportunity of examining these specimens.

� Vide Eenault (77), (96), p. 158. Zeiller (93), p. 34. Williamson and Scott (94), p. 942.

II. Types of vegetative branches of Sphenophyllum.

This species of Sphenophyllum bears verticils of six or eight wedge-shaped leaves varying in breadth and in the extent ofnbsp;dissection of the laminae; they are truncated distally, andnbsp;terminate in a margin characterised by blunt or obtusely-rounded teeth, each of which receives a single vein. Thenbsp;larger leaves are usually more or less deeply divided by a mediannbsp;slit. The narrow base of each leaf receive.s a single vein whichnbsp;branches repeatedly in a dichotomous manner in the substance

From a specimen in the Collection of Mr. E. Kidston, Upper Coal-Measures, Eadstook. f nat. size.

' Brongniart (22), p. 234, PI. n. flg. 8. nbsp;nbsp;nbsp;^ Brongniart (28), p. 68.

Bischofl (28), PI. xiii. fig. 1. nbsp;nbsp;nbsp;^ Eiimer, F. (62), p. 21, PI. v. fig. 2.

of the lamina. Several drawings have been given by Sterzel* in a memoir on Permian plants, showing the variation in leaf-form in Sphenophyllum emarginatum, but as Kidston^ andnbsp;Zeiller^ have pointed out Sterzel�s specimens probably belongnbsp;to S. cuneifolium (Sternb.).

Branches are given off singly from the nodes, and the cones are borne at the tips of branches or branchlets. The cone ofnbsp;S. emarginatum agrees very closely with that of S. cuneifolium,nbsp;and is of the same type as that shown in fig. 108. The smallnbsp;branch of S. emarginatum represented in fig. 109 does not shownbsp;clearly the detailed characters of the species, as the leaf-margin.snbsp;are not well preserved.

In one of the largest specimens of this species which I have seen, in the Leipzig Museum, the main stem has internodes ofnbsp;about 3 9 cm. in length, from which a lateral branch with muchnbsp;shorter internodes is given off from a node.

It is important to notice the close resemblance, as pointed out by Zeiller, between some of the narrower-leaved forms ofnbsp;8. emarginatum and 8. cuneifolium (Sternb.)^; but in the latternbsp;species the margins of the leaves have sharp, and not bluntnbsp;teeth.

The cone described and figured by Weiss'* as Bowmanites germanicus, since investigated by Solrns-Laubach'*, must benbsp;referred to this species. Geinitz*' figured a cone in 1855 asnbsp;that of 8. emarginatum, but his determination of the speciesnbsp;is a little doubtful. Good figures of the true cone of 8. emarginatum have been given by Zeiller* in his Flore denbsp;Valenciennes, as well as in his important memoir on the ,nbsp;fructification of Sphenophyllum.

The finely-divided leaves of the single whorl shown in fig. 110, B (from the Middle Coal-Measures of Barnsley, Yorkshire),

* nbsp;nbsp;nbsp;Sterzel (86), pp. 26, 27, etc.nbsp;nbsp;nbsp;nbsp;^ Kidston (93), p. 333.

* nbsp;nbsp;nbsp;Ibid. p. 411.nbsp;nbsp;nbsp;nbsp;5 Weiss (84), p. 201, PI. xxi. fig. 12.

afford an example of a form of SpJienophyllum which is represented by such species as S. tenerrimum Ett.h S. trichomatosuvi Stur�, and 8. myriophyllum^ Crep. Probably the specimennbsp;should be referred to 8. trichomatosum, but it is almostnbsp;impossible to speak with certainty as to the specific valuenbsp;of an isolated leaf-whorl of this form. It has long been knownnbsp;that the leaves of 8phenophyllum may vary considerably, asnbsp;regards the size of the segments, on the same plant; and thenbsp;occurrence of such finely-divided leaves has lent support tonbsp;an opinion which was formerly held by some writers, thatnbsp;Asterophyllites and 8plienophyllmn could not be regarded as well-defined separate genera. This heterophylly of 8phenophyllumnbsp;has thus been responsible for certain mistaken opinions both asnbsp;to the relation of the genus to Galamocladus'^ {Asterophyllites),nbsp;and as regards the view that the finely-divided laminae belongednbsp;to submerged leaf-whorls, while the broader segments were thosenbsp;of floating or subaerial whorls.

There is a very close resemblance between some of the deeply-cut and linear segments of a 8phenophyllum and thenbsp;leaves of Calamocladus, bu^ in the former genus the linearnbsp;segments are found to be connected basally into a narrownbsp;common sheath. The assertion� that the deeply-cut leaves occurnbsp;on the lower portions of stems is not supported by the facts.nbsp;Kidston� has pointed out that the cones are often borne onnbsp;branches with such leaves, and the same author refers to anbsp;figure by Germar, in which entire and much-divided leavesnbsp;occur mixed together in the same individual specimen. M. Zeillernbsp;recently pointed out to me a similar irregular association ofnbsp;broader and narrower leaf-segments on the same shoots in somenbsp;large specimens in the Ecole des Mines, Paris. Cones ofnbsp;8phenophyllum tenerrimum have been figured by Stur�� andnbsp;others; they are characterised by their small size and by thenbsp;dissection of the slender free portions of the narrow bracts ^

� Eenault (82), p. 84, and Newberry (91). nbsp;nbsp;nbsp;� Kidston (90), p. 62.

Another type of Sphenophyllum is illustrated by S. Thoni Mahr as shown in fig. 110, A. This species was first described

Sphenophyllum trichoniatosum, Stur. From a specimen in the Woodwardian Museum; from the Coal-Measures of Barnsley,nbsp;Yorks. A and B ^ nat. size.

by Mahi�i from the Coal-Measures of Ilmenau, and has since been figured by Zeiller and other authors. Each whorl consistsnbsp;of six large obcuneiform leaves with the broad margin somewhatnbsp;irregularly fringed. The unusually good specimen of whichnbsp;fig. 110, A, represents a single verticil was originally describednbsp;and figured by Zeiller in 1880^; it is now in the �cole desnbsp;Mines Museum, Paris.

The leaf-forms illustrated by figs. 109 and 110 are some of the more extreme types of Sphenophyllum leaves; but thesenbsp;are more or less connected by a series of intermediate forms.

For a more complete systematic account of the different species the student should consult such works as those by Coemans andnbsp;Kickxh Zeiller, Schimper, and others.

The species shown in fig. Ill has been usually described as a separate genus Trizygia, a name instituted by Royle in 1834nbsp;for some Indian fossils from the Lower Gondwana rocks ofnbsp;India'*. Zeiller'* has lately pointed out the advisability ofnbsp;including this Asiatic type in the genus Sphenophyllum. Thenbsp;slender stem bears verticils of cuneate leaves in three pairs atnbsp;each node, the anterior pair being smaller than the two lateralnbsp;pairs. The characteristic Sphenophyllum venation is clearlynbsp;seen in the enlarged leaf, fig. Ill, B.

The inequality of the members of a single whorl, which characterises this Indian plant, is sometimes met with in

* nbsp;nbsp;nbsp;For other figures of this plant, vide Feistmantel (81), Pis. xi. a and xii. a.

European species. A specimen of Sphenophyllum oblongifolium, which Prof. Zeiller showed me in illustration of this point, wasnbsp;practically indistinguishable from Trizygia^.

In some of the earlier descriptions of the Indian species the generic name Sphenophyllum^ was used by McClelland andnbsp;others, hut the supposed difference in the leaf-whorls was madenbsp;the ground of reverting to the distinct generic term Trizygia.nbsp;Now that a similar type of leaf-whorl is known to occur innbsp;Sphenophyllum, it is better to adopt that genus rather than tonbsp;allow the question of locality to unduly influence the choicenbsp;of a separate generic name for an Indian plant.

It has been pointed out in the description of Sphenophyllum, that the most widely separated families of recent plants have beennbsp;selected by different authors as the nearest living allies of thisnbsp;Palaeozoic genus. It is now generally admitted that Sphenophyllum is a generic type apart; it cannot he classed in anj'nbsp;family or subclass of recent or fossil plants, without considerablynbsp;extending or modifying the recognised characteristics of existing divisions of the plant-kingdom. The anatomical characters of the Sphenophyllum stem are such as one finds in somenbsp;recent genera of the Lycopodinae, especiallj^ Psilotum. If thenbsp;stele of Psilotum were composed internally of a solid strand ofnbsp;xylem, we should have a close correspondence between thenbsp;centripetally-developed wood of this genus and that ofnbsp;Sphenophyllum. Similar comparisons might be drawn withnbsp;other existing genera, hut the more detailed consideration ofnbsp;the affinities of the Palaeozoic plant will be more easily dealtnbsp;with after other members of the Pteridophytes have beennbsp;described. The recent discovery of an entirely new type of Carboniferous strohilus in rocks of Calciferous sandstone age on thenbsp;shores of the Firth of Forth has thrown new light on thenbsp;position of Sphenophyllum. Cheirostrobus Petty cur ensis, thenbsp;new cone which Scott has described in an able memoir, affords

certain points of contact with Sphenophyllum on the one hand and with Galamites on the other. This important question willnbsp;be dealt with after we have given an account of Gheirostrobus^.nbsp;To put the matter shortly, Sphenophyllum agrees with somenbsp;Lycopodinous plants in its anatomical features; with thenbsp;Equisetales it is connected by the verticillate disposition of thenbsp;leaves, and some of the forms of Sphenophyllum strobili presentnbsp;features which also point to Equisetinous affinities.

In his Presidential address to the Botanical Section at the British Association Meeting of 1896 Scott^ thus refers to thenbsp;Sphenophyllums:�� We may hazard the guess that this interesting group may have been derived from some unknownnbsp;form lying at the root of both Calamites and Lycopods. Thenbsp;existence of the Sphenophyllae certainly suggests the probability of a common origin for these two series.� The result ofnbsp;the subsequent investigation of the new cone Gheirostrohusnbsp;amply justifies this opinion as to the position of Sphenophyllum.

It is probable that Sphenophyllum lived during the Devonian period, but the unsatisfactory specimens on whichnbsp;Dawson has founded a species of this age, S. antiquunG, cannbsp;hardly be said to afford posttive evidence of the Pre-Carboni-ferous existence -of the genus. From the Culm rocks andnbsp;other strata older than the Coal-Measures, we have such speciesnbsp;as S. insigne (Will), Sphenophyllostachys Rdmeri (Solms-Laubach), and Sphenophyllum tenerrimum, Ett.^ while S. emar-gmatunG, Brongn. occurs in the Upper Coal-Measures and in thenbsp;Transition rocks. S. cuneifolium^ (Sternb.) has been recordednbsp;from the Transition, Middle and Lower Coal-Measures. Sphenophyllum oblongifolium, Germ.�, is recorded from Lower Permiannbsp;rocks, as is also S. ThonG, Mahr.

The comparison which has naturally been drawn .between Sphenophyllum with its slender stems bearing occasionallynbsp;dimorphic leaves, and water-plants is not, I believe, supportednbsp;by the facts of anatomy or external characters. The entirenbsp;and finely-dissected leaves do not exhibit that regularity of

relative disposition which is characteristic of aquatic plants; the two forms of leaves may occur indiscriminately on the samenbsp;branch. The well-developed and thick xylem is not in accordance with the anatomical features usually associated withnbsp;water-plants. It is true that in some living dicotyledons of thenbsp;family Leguminosae, which inhabit swampy places, the secondarynbsp;xylem is represented by a thick mass of unlignified and thin-walled parenchyma, as in the genus Aesohynomene^, from whichnbsp;the material of � pith �-helmets is obtained; but the wood ofnbsp;Sphenophyllum was obviously thick-walled and thoroughlynbsp;lignified.

It is not improbable that the long and slender stems of this plant may have grown like small lianas in the Coal-Measure forests, supporting themselves to a large extent on thenbsp;stouter branches of Calamites and other trees. The anatomicalnbsp;structure of a Sphenophyllum stem would seem to be in accordnbsp;with the requirements of a climbing plant. It has beennbsp;shewnthat in recent climbing plants the tracheae and sieve-tubes are characterised by their large diameter, a fact whichnbsp;may be correlated with the small diameter of climbing stemsnbsp;and the need for rapid transport of food material. In Sphenophyllum the tracheae of the xylem have a wide bore, and innbsp;8. insigne the phloem contains unusually wide sieve-tubes.nbsp;The central position of the stele is another feature which is notnbsp;inconsistent with a climbing habit. Schwendener and others^nbsp;have demonstrated that in climbing organs, as in undergroundnbsp;stems and roots, there is a tendency towards a centripetalnbsp;concentration of mechanical or strengthening tissue. The axialnbsp;xylem strand of Sphenophyllum would afford an efficientnbsp;resistance to the tension or pulling force which climbing stemsnbsp;encounter.

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Schiitt, F. (93) Das Pflanzenleben der Hochsee. Kiel and Leipzig, 1893. (From Hensen�s Plankton-Expedition.)

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Schweinfurth, G. (82) ,Zur Beleuchtung der Frage iiber den verstein-erten Wald. Zeit. deutsch. geol. Ges. vol. xxxiv. p. 139, 1882.

Schwendener, S. (74) Das mechanische Princip im anatomischen Bau der Monocotylen. 1874.

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Palaeozoic rocks. On Cheirostrohus, a new type of fossil cone from the Lower Carboniferous strata (Galciferous Sandstone Series).nbsp;Phil. Trans. R. Soc. vol. ci.xxxix. B. p. 1, 1897.

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Sharpe, S. (68) On a remarkable incrustation in Northamptonshii�e. Oeol. Mag. vol. v. p. 563, 1868.

Sherborn, C. D. (93) An index to the genera and species of the Fora-minifera. Smithsonian miscellaneous Collections, 856. Washington, 1893.

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28�2

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dTbantelly (Basses-Pyr�n�es). Btdl. Soc. G�ol. France, vol. xxili. [3] p. 482, 1895.

presence, dans cette flore, du genre Phyllotheca. Compt. Bend. vol. cxx. p. 1228, 1895.

Zenker, F. 0. nbsp;nbsp;nbsp;(33) Beschreibung von Galium sphenophylloides. Neues

INDEX.

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Athenatim. The author is to be congratulated on having produced a work of exceptional value, dealing with a difficult subject in a thoroughlynbsp;sound manner.

. . ,v nbsp;nbsp;nbsp;.....

�*�. nbsp;nbsp;nbsp;gt; '�nbsp;nbsp;nbsp;nbsp;11'nbsp;nbsp;nbsp;nbsp;-�� '

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1 '�	EQUISETITES.
In.	PHYLLOTHECA.
jiii.	SCHIZONEURA.
IV.	CALAMITES.
V.	ARCHAEOCALAMITES.

SiS

Eontion: O. J. OLAY and SONS, CAMBEIDGB UNIVERSITY PRESS WAREHOUSE,nbsp;AVE MARIA LANE,

H. K. LEWIS,

136, GOWER STREET, W.C.

FOSSIL PLANTS

OO0L 66^^^

AT THE UNIVERSITY PRESS. .nbsp;nbsp;nbsp;nbsp;1898

1577 0807

Cambri�ge:

PEEFACE.

TABLE OE CONTENTS.

PAET I. GENERAL.

CHAPTER I.

HISTORICAL SKETCH. Pp. 1�11.

CHAPTER II.

RELATION OF PALAEOBOTANY TO BOTANY AND GEOLOGY. Pp. 12�21.

CHAPTER III.

GEOLOGICAL HISTORY. Pp. 22�53.

CHAPTER V.

DIFFICULTIES AND SOURCES OF ERROR IN THE DETERMINATION OF FOSSIL PLANTS. Pp. 93�109.

CHAPTER VI.

NOMENCLATURE. Pp. 110�115.

PAE� II. SYSTEMATIC.

CHAPTER VII.

CHAPTER X.

EQUISETALES (continued). Pp. 295�388.

I- Historical sketch....... 295-302

II. nbsp;nbsp;nbsp;Description of the anatomy of Calamites .nbsp;nbsp;nbsp;nbsp;. 302-364

III. nbsp;nbsp;nbsp;Pith-casts of Calamites...... 365-380

CHAPTER XI.

SPHENOPHYLLALES. Pp. 389�414.

I. nbsp;nbsp;nbsp;The anatomy of Sphenophyllum .... 392-406

III. nbsp;nbsp;nbsp;Affinities,nbsp;nbsp;nbsp;nbsp;Range and Habit of Sphenophyllum . 412-414

LIST OF ILLUSTRATIONS.

PAI^T I. GENEEAL.

CHAPTER I.

CHAPTER II.

13

n]

15

S.

CHAPTER HL

24

26

];'A:

30

34

35

36

II. Cambrian.

37

III. Ordovician.

V. Devonian.

VI. Carboniferous.

41

Ill]

m]

45-

VII. Permian.

46

YIIl. Trias.

49

Upper

51

4�2

53

CHAPTER IV.

\;^y.

^......- nbsp;nbsp;nbsp;. .....wj^lC y?Srv...^-. .-^ �

IS�

61

63

64

66

67

68

70

Pil

74

76