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CAMBRIDGE BIOLOGICAL SERIES

FOSSIL PLANTS

CAMBRIDGE UNIVERSITY PRESS C. F. CLAY, Managernbsp;HDttÖon: FETTER LANE, E.C.nbsp;lEiimburgf): 100 PRINCES STREET

5-onBon: H. K. LEWIS AND CO. Ltd., LSe, GOWER STREET, W.C. JLontJon: WILLIAM WESLEY AND SON, 28, ESSEX STREET, STRANDnbsp;jjleto lotamp;: G. P. PUTNAM’S SONSnbsp;IBomfcng, Calcutta anU UKatrag: MACMILLAN AND CO., Ltd.nbsp;Coronto: J. M. DENT AND SONS, Ltd.

Coftuo; THE MARUZEN-KABUSHIKI-KAISHA

All riffhts reserved

.i

CHARLES RENÉ ZEILLER

Membre de I’lnstitut Inspecteur general des Minesnbsp;Professeur a l’École Nat*® Supérieure des Minesnbsp;(1847—1915)

¦ nbsp;nbsp;nbsp;Goo

FOSSIL PLANTS

BY

A. C. SEWARD

M.A., F.R.S., Hon. Sc.D. Dublin

PKOFESSOK OF BOTANY IN THE ÜNIVBESITT; MASTER OF DOWNING COLLEGE AND HONORARYnbsp;FELLOW OP EMMANUEL COLLEGE, CAMBRIDGE

WITH 253 ILLUSTRATIONS

Bibliotheek nbsp;nbsp;nbsp;-

Instituut voor aardwetenschappQII Budapestlaan 4nbsp;3684 CD Utrecht

VOLUME III

AT THE UNIVERSITY PRESS 1917

rijksuniversiteit UTRECHT 1577 0740

TO THE MEMORY OF MY FRIEND

CHARLES RENÉ ZEILLER

ILLUSTRIOUS AS A MAN OF SCIENCE AND A NOBLE-HEARTED GENTLEMANnbsp;WHOM TO KNOW WAS TO REVERE

PREFACE

TN the Preface to Volume II published in 1910 I rashly stated that it was my intention “to devote such space as is available within the limits of a text-book to the neglected subjectnbsp;of the geographical distribution of plants at different stagesnbsp;in the history of the earth,” also that Volume III would benbsp;completed with as little delay as possible. Though nearly sevennbsp;years have elapsed since the publication of the second volume itnbsp;may fairly be said that the delay is not entirely due to causesnbsp;which it was in my power to control. The subj ect of geographicalnbsp;distribution receives no connected treatment in Volumes IIInbsp;and IV for the simple reason that I underestimated the spacenbsp;required for the description of the Gymnosperms. The alternatives were either to insert a greatly compressed survey of thenbsp;successive floras of the world at the end of Volume IV or tonbsp;attempt a fuller and less technical treatment of the subject innbsp;a separate book. In choosing the latter course I am consciousnbsp;that a further obligation is undertaken which it may not benbsp;possible to fulfil; but the risk is deliberately taken. Volumenbsp;IV is in the press and will, it is hoped, be published before thenbsp;eud of 1917.

It is a pleasant duty to repeat my thanks to many friends who have helped me in various ways. Dr Kidston generouslynbsp;and without reserve allowed me access to his splendid collectionnbsp;of Palaeozoic plants, and the frequent occurrence of his name innbsp;the list of illustrations shows how freely I have availed myself

PREFACE

of his kindness. He has read some of the chapters and greatly-assisted me by his friendly criticism and encouragement. By reading the proofs of this volume Dr Scott has further increasednbsp;my already large debt to him. It is impossible to thank himnbsp;adequately; he not only corrected many careless mistakes butnbsp;by -wise counsel and advice he rendered me a service -whichnbsp;I greatly appreciate.

The exchange of views with Prof. Zeiller has been a constant source of profit and enjoyment, and it is hard to realise that thenbsp;completed book will not receive his kindly criticism. He wasnbsp;a singularly unselfish and generous colleague, always ready tonbsp;help fellow workers, and he had the faculty in an unusual degreenbsp;of influencing those who had the privilege of his friendshipnbsp;by his sound advice and lovable personality.

The death of Count Solms-Laubach has deprived Palaeo-botany of one of its most learned and strongest supporters. In common with all students of fossil plants I owe much tonbsp;the critical treatment of the subject in the Einleitung in dienbsp;Paldofhytologie. Prof. Jeffrey has very kindly given me severalnbsp;photographs and sections which have been of great service, andnbsp;I am similarly indebted to Prof. Zalessky. To Prof. Nathorstnbsp;my thanks are due for the great interest he has taken in mynbsp;work and for his generosity in providing drawings and showingnbsp;to me many of the treasures in the famous Stockholm Museum..nbsp;Prof. Bertrand and Prof. Lignier freely supplied photographsnbsp;and drawings of specimens in their possession, and I amnbsp;particularly grateful to them for the willingness with whichnbsp;they always responded to my requests.

Through the death of Prof. Lignier in March 1916 Palaeo-botany has been deprived of another original thinker who devoted himself with whole-hearted enthusiasm to botanicalnbsp;research and for many years faithfully served the University

PREFACE

of Caen: he was a generous friend to whom one never appealed in vain for assistance. Through the kindness of the Directornbsp;of the Indian Geological Survey I have been able to examinenbsp;several fossils from the Calcutta Museum described by Oldhamnbsp;and Morris and by Feistmantel. With the Director’s permissionnbsp;several photographs and drawings made for a forthcomingnbsp;paper to be published by the Indian Survey are reproducednbsp;in this volume. I take this opportunity of thanking friendsnbsp;in Australia who recently afforded me facilities for examiningnbsp;fossil plants in their charge, and I would especially thanknbsp;Mr A. B. Walkom of the University of Brisbane, who hasnbsp;recently undertaken an investigation of the rich plant-bedsnbsp;in the Ipswich district, for all that he did to enable me to makenbsp;the most of a very short time available for palaeobotanicalnbsp;work.

For the loan of specimens and for other help I am indebted to Prof. Bayly Balfour, Prof. Bower, Prof. Margaret Benson,nbsp;Prof. Oliver, Sir David Prain, Dr Smith Woodward, Prof. Weiss,nbsp;the Director of the Geological Survey, Dr A. H. Church, Drnbsp;Arber, and other friends. I would also acknowledge a debt,nbsp;by no means inconsiderable, to my Colleague Mr Hamshawnbsp;Thomas. Among younger friends in the Cambridge Botanynbsp;School to whom I am indebted I wish particularly to thanknbsp;Miss Ruth Holden, Miss Bancroft, Mr Sayers, Mr Dutt andnbsp;others who have rendered me willing help.

In the List of Illustrations mention is made of Corporate Bodies and individuals from whom blocks have been obtained,nbsp;and I am grateful to them for readily responding to mynbsp;apphcations.

My Wife, though prevented by more urgent calls in the later stages of my task from giving as much time to the illustrations as in the two former volumes, has contributed several

a5

Vlll PREFACE

•drawings, and my daughter Phyllis Seward has also given me much help in preparing drawings from previously publishednbsp;figures.

In spite of the vigilance and wise counsel of many friends numerous blemishes remain and for these the author is alonenbsp;responsible.

A. C. SEWARD.

Downing College Lodge,

February 10, 1917.

Note. The letters A and B added to references in the footnotes indicate that the works will be found in the Bibliographies at the endnbsp;of Volumes I and II.

TABLE OF CONTENTS

CHAPTEE XXVIII

CYC AD ALES (Recent). Pp. 1—34.

CHAPTER XXIX

PTERIDOSPERMEAE (continued from Volume ii.). Pp. 35—85.

I. LYGINOPTERIDEAE.......

Lyginopteris.........

TelaMgium 54, 55 ; Lagenostoma 55-64 ; Lagenospermimi 64-66 ; Pterüpermostrobus 66, 67.

Heterangium.........

Sphaerostoma 78-81.

CHAPTER XXX

MEDULLOSEAE........

Medullosa........ 86-109,

Myeloxylon lOd-llO •, Neuropteris 110-117; Alethopteris ¦awA Linopteris \1Z •, Trigonocarpusnbsp;nbsp;nbsp;nbsp;Codono-

theca 124-126 ; Schiltzia 126-128 ; Whittleseya 128-131 ; Dolerophylluni 132-139; Ottokaria 139-141 ; Strohilites 141, 142.

Colpoxylon.........

Ehexoxylon.........

Sutcliffia..........

General considerations svggested by the anatomical features of Medullosa .......

II. A. STBLOXYLEAE.......

Steloxylon..........

' nbsp;nbsp;nbsp;CHAPTER XXXI

PTERIDOSPERMEAE. (Foliage and seeds.) Pp. 166—174. Pecopteru Pluckeneti 166-168 ; Eremopteris artemisaefolianbsp;169-172 ; Wardia 172, 173 ; Adiantites helliduhis andnbsp;Pagenospernium Arheri 173, 174.

I. nbsp;nbsp;nbsp;MEGALOXYLEAE

Megaloxylon .

II. nbsp;nbsp;nbsp;RHETINANGIEAE

Ehetinangium.

III. nbsp;nbsp;nbsp;STENOMYELEAE

Stenomyelon .

IV. nbsp;nbsp;nbsp;CYCADOXYLEAE

Cycadoxylon

Ptych-oxylon

V. nbsp;nbsp;nbsp;CALAMOPITYEAE

Calamopitys Kalymma .nbsp;Eristophyton .

VI. nbsp;nbsp;nbsp;CLADOXYLEAE

Cladoxylon Völkelia .

VII. nbsp;nbsp;nbsp;PROTOPITYEAE

Protopitys

CHAPTER XXXIII

CORDAITALES. Pp. 214—299.

CHAPTER XXXIV

PITYEAE Pitys

Archaeopitys Callixylonnbsp;Coenoxylonnbsp;Parapitysnbsp;Mesopitysnbsp;Antarcticoxylon

i

CONTENTS

CHAPTER XXXVIII CYCADOPHYTA. Pp. 478—506.

i. nbsp;nbsp;nbsp;Bucklandia 480-490; Cycadeomyelon 490, 491;nbsp;Colymbetes 491-494 ; Cycadeolepis 494-496.

ii. nbsp;nbsp;nbsp;Carpolithus 497-500; Cycadospadix 500, 501;nbsp;Beania 502; Zamiostrobus, Cycadeostrobus 503-505; Androstrobus 505, 506.

CHAPTER XXXIX

CYCADOPHYTA (Fronds). Pp. 507—591.

I. nbsp;nbsp;nbsp;Bennettitales........

Ptilophyllum 512-529; Zamites 529-537; Otoza-mites 537-545 ; Dictyozamites 546-548; Ptero-phyllum 548-558; Cycadites and Pseudocycas

558-566.

II. nbsp;nbsp;nbsp;Nilssoniales........

Nilssonia 566-578; Ctenis 578-583; Pseudoctenis

584-587.

III. nbsp;nbsp;nbsp;Incbrtab sbdis........

Sphenozamites 587-589 ; Plagiozamites 589, 590 ; Cycadorachis 590, 591.

List of Works referred to in the Text (Vols. Ill amp; IV). Index..... .....

LIST OF ILLUSTRATIONS

Several of the illustrations are printed from blocks for which I am indebted to learned societies or to individuals. The sources from whichnbsp;clichés were obtained are mentioned within square brackets. Thenbsp;names of donors of photographs or drawings are added after thenbsp;descriptions of the figures.

Fkontispibcb. Charles René ZeUler. From a photograph given to me by Madame Zeiller.

FIG.

377. nbsp;nbsp;nbsp;Cycas circinalis. A. Mahns Smith

378. nbsp;nbsp;nbsp;Cycas revoluta. [G. B. Wieland.]

379. nbsp;nbsp;nbsp;Encephalartos horridus.....

380. nbsp;nbsp;nbsp;Cycas circinalis. [Encyclopaedia Britannioa.]

381. nbsp;nbsp;nbsp;Cycas revoluta and Zamia Loddigesii .

382. nbsp;nbsp;nbsp;Encephalartos Ohellinchii. [Camb. Phü. Soc.]

383. nbsp;nbsp;nbsp;Cycas siamensis. [Encyclopaedia Britannica.]

384. nbsp;nbsp;nbsp;Cycas circinalis ......

385. nbsp;nbsp;nbsp;Cycas Micholitzii and Zamia angustifolia

386. nbsp;nbsp;nbsp;Encephalartos Altensteinii ; Dioon edule. S. M. Wadham

387. nbsp;nbsp;nbsp;Cycadean Fronds .

388. nbsp;nbsp;nbsp;Zamia Wallisii

389. nbsp;nbsp;nbsp;Zamia integrifolia.

390. nbsp;nbsp;nbsp;Zamia Loddigesii .

391. nbsp;nbsp;nbsp;Bcnvenia spectabilis.

392. nbsp;nbsp;nbsp;Cycas pectinata, C.

and Stangeria.....

393. nbsp;nbsp;nbsp;Stangeria, Encephalartos, and Ceratozamia

394. nbsp;nbsp;nbsp;Macrozamia Preissii. [Camb. Univ. Press.]

395. nbsp;nbsp;nbsp;Zamia fioridana. [G. R. Wieland.]

396. nbsp;nbsp;nbsp;Dioon edule, Cycas circinalis, etc., Encephalartos, Bowenia

Macrozamia, Microcycas.....

397. nbsp;nbsp;nbsp;Stangeria paradoxa. [New Phytologist; A. G. Tansley.]

398. nbsp;nbsp;nbsp;Macrozamia.........

399. nbsp;nbsp;nbsp;Cycadean fohar bundles......

400. nbsp;nbsp;nbsp;Cycas Micholitzii. [Camb. Phü. Soc.]

Eristophyton fasciculare Eristophyton Beinertianwm. M. Zalesskynbsp;Cladozylon mirabile ; C. dubium ; 0. taeniatum ; Syncardianbsp;pusilla

Cladozylon Kidstoni ; C. mirabile Volkelia refracta

Protopitys Buehiana.......

Porozylon Edwardsii. 0. E. Bertrand and F. W. Oliver Poroxylon Edwardsii ; P. Boysseti. C. E. Bertrand .nbsp;Cordaites leaf. {C. Felicis.) R. Kidstonnbsp;Cordaites principalis ; Artisia transversa. R. Kidston

Cordaites Kngulatus.......

Cordaites (Rhizo-Cordaites) ; Cordaites circularis ; Cordaites sp. cf. C. Lacoei; C. crassifolius ....nbsp;Cordaites aeqvalis; C. Clerci. M. Zalesskynbsp;Cordaites (Noeggerathiopsis) Hislopi. G. R. Wieland .nbsp;Cordaites (Noeggerathiopsis) Hislopi. [Geological Society.]nbsp;Cordaites (Noeggerathiopsis) Hislopi. [Geol. Surv. India.]nbsp;Cordaites stemnbsp;475. Dadoxylon materiarumnbsp;Dadoxylon Pedroinbsp;Cordaites root

Cordaites ? root. T. N. Leslie Cordaianthus. E. E. Weiss .

Cordaianthus Pitcairniae; C. Volkmanni Cordaianthus Grand'Euryi ; C. Williamsoni ;

C. E. Bertrand Cordaianthus microsporangia .

Mesoxylon Sutcliffii

Pelourdea vogesiaca. [Geologists’ Assoc.]

Titanophyllum Grand'Ewryi .

487. Pitys antiqua ....

Pitys primaeva .....

Callixylon Trifdievi. M. Zalessky Mesopitys Tchihatcheffi, ....

Antarcticoxylon Priestleyi Diagram of a synthetic type of seed .

Lagenostoma ovoides; L.Lomaxi; Physostoma elegans; Telan glum Scotti; Stephanospermum akenioidesnbsp;Stephanospermum akenioides; Conostoma oblonga; Onetop-sis elliptica; Physostoma elegans; Mitrospermum compres-sum ...........

Polypterospermum Renaultii; Ptychotesta tenuis; Polylopho-

314

495.

LIST OF ILLUSTKATIONS

O. Bunburyanua [Encyclopaedia Britannica.]nbsp;Otommites bengalensis. [Geological Surv. India.]nbsp;Otommites Kliptsteini. [Geological Society.]nbsp;Dictyommites Hawelli ....

PteropJiyllum Jaegeri ....

Pterophyllum Nilasoni ; Nilssonia mediana Pterophyllum Fayoli ....

Pterophyllum Braunianum Pterophyllum Nafhorsti ; Nilssonia tenuicaulisnbsp;[Royal Society of Scotland.]

Pterophyllum Nilssoni.....

[Trustees of the British Museum.] Pterophyllum Lyellianum

[Trustees of the British Museum.] Pseudocycas insignis ......

Pseudocycas Saportae. [Encyclopaedia Britaimica.] Nilssonia pterophylloides ; N. brevis ; N. polymorphanbsp;Nilssonia brevis ; N. saighensis ....

Nilssonia rajmahalensis. [Geological Surv. India.] Nilssonia compta. [Trustees of the British Museum.]nbsp;Nilssonia princeps. [Geological Surv. India.]

625. Gtenis sp. [Manchester Phil. Lit. Society.]

Ctenis sulcicaulis .......

Pseudoctenis eathiensis ......

[Trustees of the British Museum.]

Sphenommites Roehei.......

Sphenozamites Belli. [Trustees of the British Museum.]

CHAPTER XXVIII.

CYCADALES (BECENr).

Among the fossil genera described in the last chapter of the second volume some were spoken of as true Ferns though mostnbsp;of them, it was added, ‘may safely be regarded as plants whichnbsp;will ultimately be shown to belong to some other group, in mostnbsp;cases that of the Pteridosperms.’ Since this was written additionalnbsp;evidence has been obtained in favour of the inclusion of certainnbsp;genera in the Pteridosperms. In the case of Taeniofteris, onenbsp;of the genera already described, there is reason to believe thatnbsp;at least one species is a member of the Cycadales and not a truenbsp;Fern as formerly supposed.

The Pteridosperms so far described are represented for the most part by sterile leaves preserved as impressions, the generanbsp;founded on more satisfactory material having been reserved fornbsp;treatment in this volume. As these genera are founded to anbsp;large extent on anatomical characters oscillating in their essentialnbsp;features between recent Ferns and Cycads, it is important thatnbsp;the student should be in possession of the anatomical characteristics of both of these classes; and for this reason a general accountnbsp;of recent Cycads is intercalated between the Pteridospermsnbsp;already described and those reserved for treatment in this volume.

The section of the Gymnosperms known as the Cycadales, J'epresented by nine recent genera and less than 100 species, is ofnbsp;exceptional importance phylogenetically and demands specialnbsp;attention from palaeobotanical students. Familiarity with thenbsp;®iorphology of recent forms is essential not only in relation to extinctnbsp;eycadean plants but also to types which, though not sufficiently close

S. Ill nbsp;nbsp;nbsp;1

CYCADALBS [CH.

to surviving species to be included with them in one class, exhibit features regarded by many botanists as indications of an affinitynbsp;either to true Cycads or to some generalised stock of which theynbsp;are an offshoot. The Cycads of to-day may fairly be spoken ofnbsp;as anachronisms, plants appropriate to a former age but out ofnbsp;harmony with the present. They are confined to tropical andnbsp;sub-troJ)ical regions in both the old and new world. In habit

Fig. 377.

many of them resemble tree-ferns, but the columnar stem, which may live to a great age and attain a height of 20 metres, differsnbsp;from that of ferns in its gradually tapered form consequent onnbsp;the presence of one or more cambial cylinders. Though oftennbsp;unbranched (fig. 377) branching of the main trunk is by no means

4

CYCADALES

unusual (fig. 378; fig. 381, B). Many Cycads are geophilous and have short tuberous stems (figs. 383, 395, 1 a; 396, E): the genusnbsp;Zamia includes a few epiphytic forms’-. The typical cycadeannbsp;stem is covered with persistent petiole-bases with or without annbsp;admixture of smaller scale-leaf bases (figs. 379, 380), while innbsp;several species a transversely wrinkled or irregularly fissurednbsp;periderm forms the superficial tissue (figs. 381, B; 383). Thenbsp;foliage-leaves are relatively large and, with the exception of thenbsp;bipinnate fronds of Bowenia (fig. 391), they are always pinnate.nbsp;The fronds usually form a terminal crown (figs. 377, 379) and

Fig. 380. Cycas circinalis. Stem sho-vving alternate zones of leaf-bases (F) and scale-leaf bases (S). (From the Encyclopaedia Britannica.)

as many as 100 may be produced from one bud. In Zamia pygmaea^ the fronds are only 10—12 cm. long, but in some cycadsnbsp;they reach a length of several metres. On both young foliage-leaves and scale-leaves long and very rarely branched® unicellularnbsp;hairs (fig. 396, N) form a characteristic feature and take the placenbsp;of the ramental scales of the majority of ferns. The apex of thenbsp;stem shown in fig. 386, A is covered with a mass of woolly hairsnbsp;and several scale-leaves are seen on the lower part of the bud.

All recent Cycads are dioecious. The reproductive shoots, except the megasporophylls of Cycas—which have departed to anbsp;less extent than those of other genera from the foliage-leaf plannbsp;(fig. 381, A; fig. 392, A—C) and are borne in a terminal cluster

XXVIIl]

through which the stem subsequently pushes its way—consist of a varying number of micro- or mega-sporophylls in densenbsp;spirals on the axis of an elongated or oval strobilus (figs. 386, B,nbsp;393, 394). The microsporophylls are occasionally verticillate^.

CYCADALES

lateral strobili bas recently been described by Chamberlain^ who figures a stem of Macrozamia Moorei with fertile shoots wedgednbsp;among the persistent petiole-bases, a condition very similar tonbsp;that in the Mesozoic Bennettitales. Pearson has also describednbsp;clear cases of laterally-borne cones in Encephalartos. Cycasnbsp;exhibits two kinds of branching, the female plants being mono-podial while in the male the branching is sympodial. The microspores are produced in sporangia grouped in more or less wellnbsp;defined sori (figs. 389, A; 392, E—G). There is no definitenbsp;annulus, but in the occurrence of groups of thick-walled cellsnbsp;some microsporangia recall those of certain ferns^. The ovulesnbsp;vary considerably in size, sometimes exceeding 5 cm. in diameter:nbsp;there are usually two on each megasporophyll (figs. 393, C;nbsp;394; 395, Id) but in most species of Cycas (fig. 392, B) andnbsp;occasionally in other genera the number is larger®. A thicknbsp;integument encloses the nucellus with which it is fused exceptnbsp;in the apical region (fig. 396, A, B). Below the comparativelynbsp;long micropylar tube is a well-developed pollen-chamber (fig. 396,nbsp;B', p), a striking feature of Cycadean ovules, immediately abovenbsp;the megaspore; the latter is filled with prothallus-tissue andnbsp;bears a small apical group of archegonia on the floor of a depressionnbsp;(fig. 396, A—B'). In Microcycas'^ as many as 200 archegonianbsp;are recorded—a very exceptional case—and these are not confinednbsp;to the apical region, though only the apical archegonia arenbsp;functional. Each archegonium is characterised by a very largenbsp;oval egg-cell and a much reduced neck®. The microspores usuallynbsp;produce a single prothallus-cell, a stalk-cell, and body-cell, andnbsp;from the body-cell are developed two spirally ciliated spermato-zoids (fig. 396, M). In this respect also the monotypic genusnbsp;Microcycas is peculiar; it may have as many as 8 body-cellsnbsp;and 16 male gametes in a single pollen-tube (fig. 396, G), whilenbsp;in Geratozamia^ 4 gametes have been seen in one tirbe. Thenbsp;pollen-tube grows like a fungal mycelium into the nucellar tissuenbsp;and the male gametes are formed in the distended proximal end

^ Chamberlain (13). nbsp;nbsp;nbsp;^ Lang (97); (00).

“ Chamberlain (09) p. 410. nbsp;nbsp;nbsp;* Caldwell (07).

® For figures and references, see Coulter and Chamberlain (10).

“ Chamberlain (12) p. 11.

Xxvill]

which on bursting liberates the motile sperms with the watery cell-sap. Fertilisation is succeeded by the development of anbsp;homogeneous proembryo partially or completely filling the zygotenbsp;(fertilised egg): by the formation of long suspensors the embryonbsp;Js brought into contact with the food-store of the prothallus.nbsp;In some Cycads, e.g. Encephalarios, the embryogeny exhibits anbsp;close resemblance to that of Ginkgo'^. The embryo is dicotyle-donous^.

The single stele of the stem is characterised by a large pith which in some genera {e.g. Encephalartos, Macrozamia) contains

anastomosing system of collateral bundles. The vascular •tissue of a cycadean stem forms a cylinder of secondary xylemnbsp;^nd phloem, the primary xylem being represented only by a few,nbsp;Usually crushed, protoxylem elements on the inner margin ofnbsp;the reticulately pitted or scalariform tracheids. Both xylemnbsp;uud phloem are traversed by numerous broad and deep medullarynbsp;rays®. The looser texture and more parenchymatous structurenbsp;cf Cycadean wood afford a ready means of distinguishing it fromnbsp;the Wood of Conifers: for the Cycadean type the term manoxylicnbsp;18 proposed and pycnoxylic for the more compact coniferousnbsp;Wood*. Eims (or ‘bars’) of Sanio, of which much has been saidnbsp;111 discussions on the phylogeny of Conifers, have recently beennbsp;described in the petiolar xylem of Cycas revoluta: the rims arenbsp;8liort and ‘cling closely to the borders of the pits,’ features whichnbsp;also characterise the rims found in the cones of the Araucarineaenbsp;^ud in the root- and cone-wood of certain Pines®. In somenbsp;Cycads the secondary xylem and phloem form a single cylinder,nbsp;but in others {Cycas, Encephalartos, Macrozamia, Bowenid) thenbsp;cambium is succeeded by one or several concentric cylindersnbsp;of meristem which have their origin in the pericycle. Thenbsp;spasmodic occurrence of separate arcs of inversely orientatednbsp;secondary xylem and phloem between the normal cylinders isnbsp;u feature of importance from the point of view of comparison

1 Saxton (10*).

for an explanation of the occurrence of a single cotyledon in Ceratommia, see Dorety (08).

® Worsdell (00); (01); Chamberlain (11).

porous, loose in texture; ttvkvÓs, compact.

Sifton (15).

CYCADALBS

with the Palaeozoic Medulloseae^. The occurrence of concentric cauline strands in the cortex of Cycas is also a peculiarity worthynbsp;of notice. Successive bands of periderm, and occasionally anbsp;considerable amount of phelloderm^, are formed in the peripheralnbsp;region of the stem.

The leaf-traces in an adult stem exhibit a striking feature in their indirect or girdle-like course to the leaves (fig. 396, H, g)nbsp;and in the gradual change from an endarch (fig. 396, 0) to annbsp;apparently mesarch structure (fig. 400) as they pass from thenbsp;perimedullary zone to the petiole: except at the base of thenbsp;petiole the vascular bundles of the frond-axis consist of (i) centri-petally developed xylem with a median protoxylem and a muchnbsp;smaller amount of centrifugal xylem (fig. 400) separated by a fewnbsp;parenchymatous elements from the centripetal xylem, (ii) annbsp;external arc of protophloem and within this metaphloem andnbsp;parenchyma®. In the slender petiole of Bowenia there are a fewnbsp;collateral bundles arranged in the form of a circle or ellipse^; innbsp;Cycas and some other genera the more numerous bundles form anbsp;pattern like an inverted U, and in some species of Encephalartosnbsp;the number is greater and the strands more irregularly scattered®.nbsp;In the vegetative stems there is no centripetal xylem in the stele,nbsp;but scattered centripetal tracheids occasionally occur internal tonbsp;the protoxylem in the steles of the peduncles®.

Cycadeae. Megasporophylls each bearing 2—8 ovules, borne separately like foliage-leaves and not in strobili. Pinnae have a midrib but no lateralnbsp;veins (figs. 384, 387, A). Cycas (fig. 377).

Zamieae. Both kinds of sporophylls form strobili. Pinnae have several dichotomously branched, more or less parallel veins. Zamia (figs. 388—390),nbsp;Macrozamia, Encephalartos (figs. 379, 386, C), Ceratozamia, Dioon (fig. 386, B),nbsp;Microcycas.

Stangerieae. Strobili as in Zamieae. Pinnae fern-like, numerous dichotomously branched lateral veins given off from a midrib. Stangeria.

Bowenieae. Leaves bipinnate (fig. 391), strobili as in Zamieae. Bowenia.

Distribution. The most widely spread genus, Cycas, occurs in Siam, India, the Nicobar Islands, Ceylon, Madagascar, and

1 Worsdell (00); (06). See postea, Chap. xxx. nbsp;nbsp;nbsp;^ Worsdell (98“).

^ For figures, see Mettenius (60) B.; de Bary (84) A.; le Goo (14); Marsh (14).

^ Wieland (06) pp. 62, 63.

5 Matte (04) PI. vii. fig. 111. nbsp;nbsp;nbsp;« Scott (97); Matte (04) p. 164.

DISTRIBUTION

Australia, in many of the islands in the Indian and Pacific oceans, in New Guinea, Borneo, New Caledonia, New Britain, China andnbsp;Japan^. Zamia, the most northerly genus, extends from Northnbsp;Mexico and Florida through Central America and some of thenbsp;M^est Indian islands to Ecuador, Bolivia, Chile, and Peru. Dioonnbsp;and Ceratozamia are confined to South Mexico, and Microcycasnbsp;flourishes on the Cuban mountains. The continent of Africanbsp;possesses two endemic genera Encephalartos and Stangeria. Ence-phalartos extends from Cape Colony through Natal and Zululandnbsp;to Zanzibar and Mombasa^; a specimen in the Kew Herbariumnbsp;(probably E. Hildebrandti) is said to have been collected as farnbsp;north as the Soudan. Two species are recorded from the Congo®nbsp;and E. Barteri, discovered by Barter in Central Africa, is recordednbsp;from the Gold Coast^. Stangeria has a much more limited rangenbsp;in S.E. Africa®; Australia possesses Macrozaniia, represented bynbsp;Several species in Western Australia, New South Wales andnbsp;Queensland, Oycas in Queensland and the Northern territorynbsp;and the Queensland genus Bowenia. There are no Cycads innbsp;New Zealand. As a whole Cycads have a limited range and withnbsp;the exception of Cycas and Zamia none of them extend beyondnbsp;the limits of a single continent. They are as a rule not gregariousnbsp;plants and play a subordinate part in the facies of the vegetation,nbsp;flfacrozamw forms dense thickets® in some districts and occursnbsp;both in exposed situations and in association with Palms innbsp;flamp Queensland forests. Chamberlain^ speaks of 100 plants ofnbsp;Jdioon edule as visible in one view in South Mexico where thenbsp;apecies forms a mountain forest. In Florida Zamia -pumila^nbsp;grows in dense moist woods, a habitat in contrast to that of manynbsp;fllycads. The Mexican Ceratozamia is associated with luxuriantnbsp;'^egetation, while its compatriot Dioon^ lives in blazing sunshine.

^ The species Cycas taiwanensis was founded by Mr Carruthers (93) on material rota Formosa, and C. revoluta has also been recorded from Formosa [Thiselton-yer (02) p. 559], but according to Mr Elwes it is very doubtful whether anynbsp;native Cycad occurs on the island.

' Engler (95) p. 92; Stapf (14).

“ Card. Chron. June 11, 1904, p. 370.

* Bot. Mag. 1909, Tab. 8232. nbsp;nbsp;nbsp;^ Pearson (06).

Chamberlain (12^). nbsp;nbsp;nbsp;’ Chamberlain (06).

Webber (01). nbsp;nbsp;nbsp;* Chamberlain (09).

Sir Joseph Hooker^ speaks of Cycas living in the deepest and hottest valleys in Sikkim. Encephalartos is essentially a xero-philous genus. Stangeria paradoxa is said to be confined to forestsnbsp;in Cape Colony, and another species grows among the grass ofnbsp;the Park-lands in open country^. While it is true that manynbsp;Cycads are characteristic of dry regions some species flourishnbsp;in places where shade and moisture are abundant.

Though it is impossible in many cases to form an estimate of the age of individual plants, there are clear indications thatnbsp;some specimens afford notable instances of longevity. Chamber-lain estimates the age of some plants of Dioon spinulosum asnbsp;exceeding 400 years and mentions an example of D. ednle thatnbsp;is probably 1000 years old. An unusually tall plant of Encephalartos in the Botanic Garden of Amsterdam is believed by Prof, denbsp;Vries to have reached the venerable age of 2000 years®. Thenbsp;restricted range and in many cases the solitary existence of recentnbsp;Cycads, with their tall stems clothed with the persistent cork-covered stumps of thousands of fronds, deepens the impressionnbsp;of antiquity derived from a study of the geological history ofnbsp;this dwindling race.

Stems. The tall columnar stems of some species of Cycas, often branched or bearing numerous ovoid buds like enlargednbsp;bulbils^, are characterised by the regular alternation of large andnbsp;small leaf-bases as seen in the stem of C. circinalis reproducednbsp;in fig. 380. In older stems of this species the leaf-bases arenbsp;exfoliated and the stem is covered with wrinkled and fissurednbsp;cork; but in Cycas revoluta the leaf-bases are even more persistent.nbsp;The columnar but relatively stout stems of Encephalartos (figs.nbsp;379, 382, 386, A) and Ceratozamia are similarly encased in anbsp;covering of petiole-bases, but in these genera the differencesnbsp;between foliage-leaves and bud-scales is much less obvious andnbsp;there is no zonal alternation. On the stems of Macrozamia thenbsp;rhomboidal leaf-bases are more uniform in size and there are nonbsp;scale-leaves. The tall and often palm-like stems of Microcycas

’ Hooker, J. D. (91) A. p. 98 (footnote). nbsp;nbsp;nbsp;^ Pearson (06).

^ Prof, de Vries kindly informed me in a letter that this estimate is not to be regarded as anything more than a rough guess.

* Stopes (10).

sometimes show ti'ansverse rings on the bark marking the position of former terminal bnds, and in older trunks these may disappear,nbsp;leaving a fissured bark^. In Cycas siamensis the tuberous stem

is similarly covered with a rough bark (fig. 383) and the stems of Zamia are also characterised by an absence of persistent leaf-bases (figs. 381, B; 39-5, In, a). It is pertinent to remind the

1 Caldwell (07).

palaeobotanical student of the occurrence of flowering plants with stems closely simulating those of some Cycads. Prof. Bower^nbsp;in describing Rhynchopetalum montanum, an Abyssinian Lobelia-ceous plant, drew attention to the similarity in surface-featuresnbsp;and to some extent in anatomical structure to cycadean stems.nbsp;The resemblances are further emphasised in a more recentlynbsp;published account of the same species under a different name,nbsp;Lobelia Rhynchopetalum^.

Fronds. A general acquaintance with the various types of fronds illustrated by recent Cycads is important to the studentnbsp;of fossils not only to enable him to compare existing and extinctnbsp;forms but as affording safeguards against possible sources of errornbsp;in the description and identification of impressions®. The vernation exhibits less uniformity than in Ferns: in Cycas the rachisnbsp;is straight and the pinnae circinately coiled (fig. 220, B, vol. ii.nbsp;p. 283); in Zamia and Stangeria the rachis is bent and the pinnaenbsp;straight, while in Ceratozamia and other genera both the axisnbsp;and leaflets are straight. As Braun pointed out, there is as anbsp;rule no terminal leaflet, or it may be pushed to one side givingnbsp;a forked appearance to the frond apex^.

1 Bower (84).

® Seward (95) A. pp. 15 et seq.

are forked as in Cycas Micholitzii^ (fig. 385). Several years ago I noticed a similar instance of concrescence in a small plant of C. circinalis in the Royalnbsp;Gardens, Kew (fig. 387, I). In Cycas Micholitzii the pinnae, reaching a lengthnbsp;of 20 cm., are repeatedly and deeply forked (fig. 385, A, B; fig. 400): thenbsp;pinnae of C. Rumpliii var. bifida^ are also deeply dissected. Cycas Beddomeinbsp;has very narrow pinnae (15 cm. x 2 mm.) similar to those of the Wealden

Thiselton-Dyer (6S) B.; Bot. Thiselton-Dyer (02) p. 560.

species Cycadites Saportae, and it is noteworthy that narrow leaflets with a strongly revolute lamina would produce casts with two parallel ribs (thenbsp;grooves between the midrib and the edge of the lamina) simulating the doublenbsp;midrib of the fossil genus Pseudocycas. In some fronds, e.g. C. Cairnsiana,nbsp;the midrib is hardly visible on the upper face of a dried pinna which shows anbsp;longitudinal wrinkling simulating parallel venation.

Fig. 385. A,Ti, Cycas Micholitzii. (After Thiselton-Dyer.) C, Zamia angustifolia.

Encephalartos. The fronds of this genus, in Encephalartos Lanrentianus^ reaching the exceptional length of 7 metres, bear alternate pinnae exhibitingnbsp;a considerable range in form and breadth. In E. longifolius, E. Altensteiniinbsp;(fig. 386, C), E. Lehmanni, etc., the pinnae are for the most part linear, reachingnbsp;a length of 20 cm. and a breadth of 2 cm.: in E. cajfer (fig. 387, D), E. latifolius,nbsp;and others the pinnae are broader and shorter and often spinous. A frond ofnbsp;E. longifolius or E. Altensteinii may bear both entire and lobed, spinousnbsp;pinnae. In E. Frederici-Guilielmi (fig. 387, G) and E. GheUinclcii^ (fig. 382)nbsp;the pinnae are very narrow and almost filiform, with revolute edges. Thenbsp;thick and leathery pinnae of some species are attached obliquely to the edge or

Gard. Chron. 1904, June 11, p. 370.

to the upper sloping sides of the rachis which forms a prominent ridge between the rows of leaflets, and characteristic oval scars are left on the fall of thenbsp;pinnae (fig. 387, D, G'). The lamina in most species contains several veinsnbsp;more or less parallel to the margins and often much more prominent on thenbsp;lower than on the upper surface.

I'lG. 387. Cycadean fronds. A, Cycas circinalis; B, Macrozamia Fraseri; C, Macrozamia Dcnisoni-, D, Encephalartos cajfer; E, P, Dioon edule fromnbsp;below and above; G, Encephalartos Frederici-Guilielmi, G', side-view;nbsp;H, Ceratozamia mexicana; I, Cycas circinalis, lower part of young frond.

Zamia. In Zaniia angustifolia (fig. 385, C) and Z. linifolia the pinnae are long and very narrow: the other extreme is represented by Z. Wallisii^nbsp;(fig. 388) with broad ovate segments reaching a length of nearly -5 metrenbsp;and attached to the rachis by a short stalk; the veins are prominentnbsp;and dichotomously branched. Other forms of pinnae are represented bynbsp;Z. integrifoUa, Z. floridana, and Z. Loddigesii (figs. 389, 390, 395). Thenbsp;1 Braun, A. (75®) p. 376.

broad and short pinnae of Z. furftiracea^ bear a close resemblance, except in the absence of an auriculate base, to those of some species of the fossil gennsnbsp;Otozamites. The broadly linear pinnae ofnbsp;nbsp;nbsp;nbsp;(45 cm. x 3 cm.)

often show longitudinal wrinklings on drying which suggest comparison with the corrugated lamina of the fossil species Nilssonia brevis. A basal pad ornbsp;callosity on the slender bases of the pinnae is characteristic of many Zamianbsp;fronds.

Ceratozamia. The fronds bear a fairly close resemblance to those of Macrozainia: in Ceratozamia mexicana the linear pinnae reach a length ofnbsp;over 30 cm. and a breadth of 2—3 cm.; the lamina tapers to a narrow apexnbsp;and is more abruptly contracted at the base (fig. 387, H). The veins innbsp;Ceratozamia are sub-parallel and dichotomy occurs up to the middle of thenbsp;lamina^. A striking feature is the occurrence of two opposite stipule-likenbsp;projections a short distance above the base of the petiole.

Macrozamia. A noteworthy feature in some species is the attachment of the linear pinnae along the middle line of the rachis (fig. 387, C); in othersnbsp;(fig. 387, B) the leaflets are attached laterally and may have a basal callosity.nbsp;The parallel veins, which branch dichotomously near the base of the lamina,nbsp;are often much more prominent on the lower than on the upper face. Innbsp;M. heteromera^ (fig. 396, F, F') the narrow pinnae are deeply forked andnbsp;strongly revolute. The spirally twisted rachis of M. spirahs, M. heteromera,nbsp;®tc., is a striking feature recalling the Bhaetic fern Camptopteris spiralis

Xath^.

Dioon. The arrangement of the linear pinnae of D. edule (fig. 386, B), -D. spinulosum, and D. Purpusii^ forms a ready means of distinguishing thenbsp;fronds of this genus: the pinnae, often contiguous and at right-angles tonbsp;the rachis, are attached in a lateral groove by an expanded and slightlynbsp;deourrent base. The difference between the lower and upper face of a frondnbsp;(fig. 387, E, F) affords a good illustration of a common source of error in thenbsp;identification of fossil specimens. The leaflets of D. spinulosum, whichnbsp;except in their spinous margin are very similar to those of D. edule, maynbsp;reach a length of 15 cm. and a breadth of 8 mm. The parallel veins are

Unbranched®.

Microcycas’’. The pinnae of this genus, very like those of the Wealden species Zamites Buchianus, reach a length of 20 cm. and a breadth of 8 mm.:nbsp;on falling they leave oblong scars resembling those on the rachis of Encepha-lartos.

Etangeria. This genus is particularly interesting because of its fern-like habit and venation. The large fronds of S. paradoxa^ bear broadly linear

1 Bot. Mag. 1818, Tab. 1969. nbsp;nbsp;nbsp;* Matte (04) p. .34.

® Seward (95) A. p. 5; Robertson (02) fig. 4.

‘ Vol. II. fig. 287, p. 389. nbsp;nbsp;nbsp;® Chamberlain (09).

® Braun, A. (75); Bornemann (56) A. PI. x.

’ Caldwell (07); Caldwell and Baker (07).

* Bot. Mag. 1859, Tab. 5121.

2-^2

diverge slightly. Both entire and serrate pinnae may occur on the same plant, but Chamberlain has revived André’s specific term serrulata in preferencenbsp;to the generally adopted designation for the serrate forms, B. spectabilisnbsp;var. serrata^.

Reproductive shoots^. In Cycas circinalis, C. Rumphii, and other species the megasporophylls reach a considerable length andnbsp;bear several lateral ovules each of which may be as large as a

^ Vol. n. p. 485. nbsp;nbsp;nbsp;2 ijgnier (94).

* Chamberlain (12®).

For information on the anatomy of reproductive shoots, see Thibout (96); Scott (97); Worsdell (98); Matte (04).

goose’s egg: the sterile distal end has the form of a spear-point with an irregularly serrate edge. In G. revoluta, C. pectinata, etc.,nbsp;the sterile part is deeply dissected and may break off (fig. 392, A)nbsp;from the fertile portion of the sporophyll. The megasporophylls

of C. Riuminiana exhibit a striking variation in form (fig. 392, B, C); some are 15 cm. long with several ovules, while others,nbsp;reduced to 8 cm., bear only two ovules and resemble the sporo-phylls of Dioon. In all other genera the megasporophylls are

aggregated into cones, but in Dioon the strobili are characterised by their more ovoid form and by the looser arrangement of thenbsp;sporophylls (fig. 386, B), each of which consists of a horizontalnbsp;stalk expanded distally into a broadly lanceolate upturned endnbsp;covered with a thick felt of hairs and bearing at its base usuallynbsp;2, rarely 5—6, ovules on cushion-like swellings. In Dioon sfinu-losum the cones may be 50 cm. long. Between the cones ofnbsp;Microcycas, over 90 cm. long, and those of some Zamias, a fewnbsp;centimetres long, there are many intermediate forms. The

T

\

Fie. 394. Macrozamia Preissii, megastrobilus and (A) single megasporophyll; a, axis of cone; JJ, stalk of megasporophyll; s, unripe seeds. (After Rendle.)

large strobilus of an Encephalartos reproduced in fig. 393, D, shows the convex ends of the sporophylls with a jagged edge,nbsp;and in monstrous cones the marginal lobes may be abnormallynbsp;developed and assume the appearance of pinnae^. Each megasporophyll bears two large ovules (fig. 393, B). In certain speciesnbsp;of Encephalartos the swollen ends of the sporophylls have a truncate centre like the flattened umbo of some Pines (fig. 392, D).nbsp;The presence of two divergent spines is a peculiarity of the mega-

^ Thiselton-Dyer (01); Bot. Mag. 1915, Tab. 8592, 8593. For instances of monstrous cones, see Miquel (69), Wieland (02).

sporophylls of Geratozamia (fig. 393, C): in Macrozamia (fig. 394) the distal ends are prolonged as tapered processes. The surfacenbsp;of the strobilus of Stangeria is formed by imbricate and rounded

ends of sporophylls (fig. 392, H) not unlike the cone-scales of Pinus excelsa or P. cembra. The megasporophylls of Zamia arenbsp;expanded into regular cushion-like hexagons with a flat centralnbsp;area (figs. 389, B; 395, 16).

The microsporophylls (figs. 389, A; 392, E) are in all genera

aggregated into strobili which often bear a close resemblance to seed-cones (fig. 393, A). On a single sporophyll of Cycas circinalisnbsp;there may be as many as 700 sporangia while in Zamia floridananbsp;there are only two microsporangia. The spore-output is largenbsp;and in extreme cases, e.g. in Dioon spinulosum, the average numbernbsp;of spores in a sporangium is said to be 30,000^.

Seeds. In the great majority of recent species the seeds may be described as large and afford a striking contrast to the smallnbsp;seeds of the Mesozoic Bennettitales. A feature of interest fromnbsp;the point of view of comparison with Palaeozoic seeds is thenbsp;absence of a resting stage, germination in some cases followingnbsp;seed-fall without an interval. As Warming pointed out, thenbsp;embryo is often undeveloped when the seeds are shed. Annbsp;interesting fact is recorded by Capt. Dorrien-Smith^ with regardnbsp;to seed-dispersal: he describes the heavy pebble-like seeds of anbsp;Macrozamia as being hurled from the ripe cones a distance of 12 ft.nbsp;The seeds of Cycas are platyspermic; the woody shell exposednbsp;on removal of the outer flesh is slightly flattened and has twonbsp;prominent angles, but three-angled seeds may occur as in Ginkgonbsp;biloba (fig. 631, C). In other genera the seeds are radiospermic.nbsp;The seed of Encephalartos Altensteinii^ (fig. 396, T)) has a square-cut distal end with a small papiUa at the summit of the unusuallynbsp;long micropylar canal (17 mm.). The stone of this seed (fig. 396, C)nbsp;shows parallel curved ridges which mark the position of vascularnbsp;strands in the inner region of the outer flesh. The large oyulesnbsp;of Cycas circinalis^ have an integument 1 cm. thick consisting ofnbsp;s-n outer and inner flesh and an intervening stony layer whichnbsp;reaches its greatest development at the base and apex. Threenbsp;vascular strands enter the base of the seed, the concentric strandnbsp;breaks up in the broad inner flesh into a group of bundles whichnbsp;cnibrace but do not penetrate the lower end of the nucellus.nbsp;Each of the two lateral strands branches in the outer flesh nearnbsp;its entrance into the seed; the outer and larger collateral andnbsp;mesarch bundle passes up close to the surface of the shell to thenbsp;seed-apex, while the inner branch penetrates the shell and,nbsp;occasionally branching, passes up the inner region of the inner

® Dorrien-Smith (11) p. 287.

^ Stopes (04) p. 438, fig. 1; Warming (77) PI. III.

flesh as far as the micropyle. In other seeds the tracheal supply of the outer flesh consists of several bundles and not two as innbsp;Cycas. The inner flesh abuts on the nucellus and is connectednbsp;with it except at the apex (fig. 396, B). In ripe seeds the nucellusnbsp;is reduced to a thin membrane enclosing the large megaspore atnbsp;the upper end of which is a depression (fig. 396, B') or sometimesnbsp;two depressions (fig. 396, I) in the prothallus containing thenbsp;archegonia. In the seed of Dioon edule^ (fig. 396, A) the positionnbsp;of the absciss-layer (s) is indicated by a slight transverse constriction. In the seeds of Bowenia, constructed on the samenbsp;plan, the inner series of vascular strands appears to be nucellarnbsp;in position, thus differing from the strands in Dioon, Cycas, andnbsp;other genera which are confined to the integument. Miss Kershaw^nbsp;in describing Bowenia speaks of an upper and a lower pollen-chamber ; the former serves as a storage-place for the microspores

^ Chamberlain (06).

Eig. 396. A. Seed of Dioon edule in longitudinal section; a, integument;

V, vascular tissue; m, prothallus; n, nucellus; p, pollen-chamber; s, absciss-layer; ar, archegonia. (After Chamberlain.)

B, nbsp;nbsp;nbsp;W. Seed of Cycas circinalis; a, v, integumefit (sarcotesta) and

vascular tissue; 6, sclerotesta; c, inner sarcotesta; m, n, prothallus and nucellus. (After Stopes.)

B'. Apex of nucellus; p, pollen-chamber; i, integument; n, nucellus; eh, archegonial chamber; ar, archegonia.

C, nbsp;nbsp;nbsp;D. Seed of Encephalartos Altensteinii; C, surface of stone. (After

Stopes.)

E. nbsp;nbsp;nbsp;Stem of Bowenia serrulata; g, level of ground. (After Chamber-

lain. )

F, nbsp;nbsp;nbsp;F'. Pinnae of Macrozamia heteromera.

6. PoUen-tube of Microcycas Calocoma. (After Caldwell.)

H. nbsp;nbsp;nbsp;Transverse section of stem of Encephalartos horridus; s, stele;

g, girdle-bundles. (After Mettenius.)

I. nbsp;nbsp;nbsp;Apical view of prothallus of Cycas showing two archegonial chambers

{eh). (After Treub.)

K. nbsp;nbsp;nbsp;Encephalartos Barteri. Transverse section of stem; x, xylem;

?, nbsp;nbsp;nbsp;phloem. (After Matte.)

L. nbsp;nbsp;nbsp;Cycas siamensis. Transverse section of vascular tissue of young

stem. (After Matte.)

M. nbsp;nbsp;nbsp;Cycas revoluta-, two motile sperms. (After Miyake.)

N. nbsp;nbsp;nbsp;Long hair with short basal cell from the petiole of Macrozamia

heteromera. (After Robertson.)

O. nbsp;nbsp;nbsp;Vascular bundle of Dioon edule from base of petiole; p, phloem;

?, nbsp;nbsp;nbsp;cambium. (After Mettenius.)

prior to their further development in the lower chamber. Dr Stopes^ regards the integument as double in origin, a viewnbsp;suggested by Griffith^ in 1835, and as homologous with the singlenbsp;integument plus the cupule of Lagenostoma. This view is supportednbsp;by Mrs Thoday®: on the other hand Miss Kershaw’s investigationnbsp;of Bowenia seeds leads her to regard the integument as single.nbsp;Although there would seem to be a prima facie case in favour ofnbsp;the dual nature of the integument, the arguments on the othernbsp;side have greater weight'^.

Recent observations point to the probability that insects play a part in the pollination of cycadean ovules. Kraus® drewnbsp;attention to the strong smell emitted by the microstrobili ofnbsp;Dioon edule and noticed that small bees were attracted to thenbsp;ripe strobili of Macrozamia, while odourless cones of a neighbouringnbsp;Ceratozamia received no attention. Pearson® and Rattray^ havenbsp;obtained evidence that beetles and weevils act as pollinators tonbsp;species of Encephalartos.

Anatomical features. Allusion has already been made to some of the more striking anatomical features; the large pith, thenbsp;occasional occurrence of medullary vascular bundles, the presencenbsp;of one or more cambiums, the large size of the medullary rays,nbsp;etc. It is worthy of remark that the occurrence of an anastomosingnbsp;system of medullary bundles is not a constant feature within anbsp;genus; in Macrozamia Fraseri such a system is present, butnbsp;absent in M. Denisoni^. In the pith of stems with no medullarynbsp;bundles cylinders of collateral bundles may occur in connexionnbsp;with a fertile shoot. These bundles arise from the inner face ofnbsp;the main cylinder and pass upwards as a domical system intonbsp;the base of the terminal strobilus which is eventually pushed tonbsp;one side by the growth of a lateral bud®. The secondary xylemnbsp;tracheids are usually provided with several rows of borderednbsp;pits on the radial walls and resemble those of the Araucarieaei®,nbsp;but in Cycads the pits are often not contiguous and less compact

1 Stopes (04). nbsp;nbsp;nbsp;2 Oliver (13).

® Thoday (Sykes) (11); Sykes (10); Thoday (Sykes) and Berridge (12).

« Salisbury (14) p. 72. nbsp;nbsp;nbsp;s Kraus (96)'.

® Pearson (06). nbsp;nbsp;nbsp;’ Rattray (13).

* Worsdell (96); (01). nbsp;nbsp;nbsp;» gee ante, p. 5.

Chamberlain (11); Wieland (06).

in tKeir distribution. The wood of Stangeria is peculiar in consisting of scalariform tracheids^ (fig. 397). Chamberlain describes growth-rings in the wood of Dioon; but this is exceptional. Innbsp;tangential sections of the stele leaf-trace bundles are constantlynbsp;seen passing horizontally through the broad and deep medullarynbsp;rays. The pith-cast of a cycadean stem reproduced in fig. 398nbsp;shows the wide meshes in the reticulum of tracheal tissue originallynbsp;occupied by parenchyma, which on decay left lenticular depressions

re

Pig. 398. Pith-cast of a Maerozamia stem, (f nat. size.)

represented on the cast by tapered convex areas occasionally bearing the impress of an outgoing trace in the form of a narrownbsp;groove. The secondary phloem often rivals the xylem in breadthnbsp;and is not always easily distinguishable from it; it consists ofnbsp;sieve-tubes, parenchyma, and fibres. The secondary cambialnbsp;cylinders characteristic of Cycas, Encephalartos, Maerozamia, andnbsp;Bowenia, to which reference was made in the summary ofnbsp;anatomical features, arise in the pericycle, and a few layers of

^ Pavolini (09); Marsh (14).

pericyclic parenchyma occur between adjacent extrafascicular cylinders of xyleni and phloem. In a stem of Cycas media 35 cm.nbsp;in diameter examined by Worsdell there were 12 concentricnbsp;cylinders. Matte^ and Miss Dorety^ have described partiallynbsp;flattened arcs of extrafascicular xylem and phloem in the hypo-cotyl of Ceratozamia mexicana. Worsdell® first drew attentionnbsp;to the occasional occurrence of short tracheids on the inner edgenbsp;of the secondary wood and to the spasmodic development ofnbsp;cambial arcs in the tissue between the extrafascicular cylindersnbsp;forming strands of inversely orientated xylem and phloem. Morenbsp;recent work by Matte gives support to Worsdell’s comparisonnbsp;between Medullosean stems and those of recent Cycads withnbsp;inversely orientated arcs or concentric vascular cylinders. Thenbsp;French author draws attention to the close resemblance betweennbsp;the seedling stems of such species as Encephalartos Barterinbsp;(fig. 396, K) and Cycas siamensis (fig. 396, L) with their polystelicnbsp;type of structure and the adult stems of Medullosa^. In thenbsp;stems of Dioon, Microcycas, Stangeria, and Zamia no extrafascicular cylinders are recorded. Two main vascular bundles enternbsp;the cortex from each leaf-base and in most stems these divergenbsp;right and left and more or less completely encircle the stele beforenbsp;passing through the medullary rays and joining the inner portionnbsp;of the xylem of the stele either as double or single bundles. Thesenbsp;girdle-bundles (fig. 396, H) first described by Karsten and Metteniusnbsp;form a very characteristic cycadean feature®. Adjacent girdlesnbsp;are joined by connecting cortical bundles and, in addition, therenbsp;are cauline collateral bundles in the cortex which form annbsp;anastomosing system. In some cases, e.g. species of Macrozamianbsp;and occasionally in Stangeria, the female peduncle of a Ceratozamia, and in seedlings of Bowenia and Cycas revoluta^, the leaf-traces pursue a direct course from petiole to stele as in stems ofnbsp;Bennettitales. It is noteworthy that in seedlings of Microcycas’’,nbsp;a .genus characterised by a large number of male gametes—nbsp;presumably a primitive feature—the leaf-traces are of the girdle-type. The two bundles at the base of a petiole by repeated

1 Matte (08). nbsp;nbsp;nbsp;^ Dorety (08^); (09).nbsp;nbsp;nbsp;nbsp;^ Worsdell (96).

^ Matte (04) especially pp. 185—202. See also Worsdell (00); (06) etc.

5 Matte (04) p. 210. nbsp;nbsp;nbsp;« Worsdell (98^).nbsp;nbsp;nbsp;nbsp;' Caldwell (07).

subdivision give rise to the numerous collateral strands of the rachis. A leaf-trace in its passage to the leaf is like that of a Conifer innbsp;having the protoxylem on its inner edge, whereas in the petiolenbsp;and elsewhere in the frond it is characterised by an arrangementnbsp;of the xylem that has usually been described as mesarch. A typicalnbsp;Vascular bundle from a cycadean frond is seen in fig. 399, C; bynbsp;far the greater part of the xylem is centripetal, the centrifugalnbsp;xylem being confined to an arc of scattered tracheids or a smallnbsp;strand separated by a few parenchymatous cells from thenbsp;protoxylem.

-px

O ogt;.v

399. Sketches illustrating the changes in the structure of Cycadean vascular bundles in their course from stem to leaf: cp, cf, centripetal and centrifugalnbsp;xylem; p, phloem; px, protoxylem. (After Marsh.)

As considerable stress has been laid on the anatomical features of the cycadean foliar bundles in discussions on the affinities andnbsp;Phylogeny of certain Palaeozoic genera, it is important to considernbsp;the facts more closely^. French anatomists described the cycadeannbsp;bundle as diploxylic on the ground that the centripetal andnbsp;centrifugal xylems are distinctly different things, the centripetalnbsp;Xylem being primary—a relic of a former organisation—andnbsp;fhe centrifugal xylem secondary and homologous with the normal

^ Carano (04); le Goc (14); Marsh (14).

wood of the cauline bundle. The term mesarch has in recent years been applied to the cycadean type of bundle. A mesarchnbsp;bundle is, however, one in which centripetal and centrifugalnbsp;xylem are alike in origin, both being primary structures derivednbsp;from a desmogen strand. Typical mesarch bundles occur innbsp;several recent ferns; in the stele of the Osmundaceae, Gleichenia,nbsp;and other genera; but in these plants the xylem is all producednbsp;directly from one primary desmogen region and there is nonbsp;question of ‘primary’ and ‘secondary’ as in the two portions ofnbsp;the xylem of a cycadean bundle. Eecent researches into thenbsp;development of cycadean foliar bundles show that they do notnbsp;conform to the mesarch type as generally understood. A leaf-trace at the base of. a petiole (fig. 399, A) comprises centrifugalnbsp;xylem only, and this consists of regular rows of tracheids separatednbsp;by medullary rays; in the lower part of the petiole the structurenbsp;is gradually modified, the centrifugal xylem is reduced andnbsp;the formation of centripetal xylem is initiated. At a highernbsp;level (fig. 399, B) the centripetal xylem is in excess of thenbsp;centrifugal and the latter, for a time connected with the former,nbsp;eventually becomes separated by a few parenchymatous cellsnbsp;from the protoxylem and persists as a small strand or arc ofnbsp;tracheids. Fig. 399 illustrates stages in the transformation ofnbsp;a typical collateral bundle, at the base of a Stangeria petiole,nbsp;into one in which the xylem is almost wholly centripetal at anbsp;higher level in the axis of the frond. A cambium is present innbsp;all: in B the centrifugal xylem is more or less clearly differentiatednbsp;into two portions, loosely arranged tracheids near the phloem,nbsp;and the more compact groups abutting on the centripetal xylem:nbsp;figs. C—E show a further reduction in the centrifugal tracheids.nbsp;The conclusion drawn from developmental study is that the twonbsp;xylem portions of the bundle are independent in origin^. Marshnbsp;has, however, shown that in Stangeria bundles near the base ofnbsp;the petiole the centrifugal xylem consists of rows of secondarynbsp;tracheids and an inner portion not in rows which connects thenbsp;centrifugal with the centripetal elements; this connecting portion,nbsp;he adds, is ‘probably primary and connects up the Cycadean foliarnbsp;bundle with the truly mesarch bundle of the Cycadofilices.’

* Le Goc (14); Marsh (14).

petiole is abundantly supplied with secretory canals and in the liypodermal region is a cylinder of stereome. In some petioles,nbsp;^¦9- Macrozamia heteromera^, the ground-tissue cells are lignifiednbsp;and reticulately pitted, a feature met with in some Mesozoicnbsp;cycadean leaves®. In Cycas media Worsdell noticed a tendencynbsp;^ Seward (06).nbsp;nbsp;nbsp;nbsp;^ Robertson (02).nbsp;nbsp;nbsp;nbsp;® Seward (12^).

S. Ill nbsp;nbsp;nbsp;3

of the leaf-trace bundles towards a concentric arrangement and similar vascular strands are recorded in the peduncle of Dioonnbsp;edule, in various sporophylls^ and in other cases. It is possible,nbsp;as Worsdell believes, that the fairly frequent occurrence of concentric bundles in plants characterised by collateral bundles maynbsp;have a phylogenetic significance.

The pinnae are dorsiventral and the veins exarch or pseudo-mesarch: secretory canals occur between {Ence-phalartos), above, or below the veins. The mesophyll of Cycas is characterised bynbsp;the presence of isolated xylem-elements passing from the midribnbsp;to the edge of the lamina and, as Lignier^ suggests, these may benbsp;regarded as a reduced system of lateral conducting strands.

The epidermal cells of the leaflets have straight or slightly curved walls except in Stangeria where they are undulate and fernlike®. The stomata, with few exceptions confined to the lowernbsp;epidermis, are larger than in other gymnosperms (on the averagenbsp;•075 X -034 mm.) and are more or less depressed below the surface;nbsp;the guard-cells are usually surrounded by 4—6 subsidiary cells.

The roots exhibit no feature to which attention need be called; the pericycle is several cells broad and as in the stem there maynbsp;be extrafascicular cylinders of xylem and phloem.

1 Worsdell (98). nbsp;nbsp;nbsp;2 Lignier (92).

^ Nestler (95); Porsoh (05); Thomas and Bancroft (13); Dusanek (13).

CHAPTER XXIX.

PTERIDOSPEBMEAE.

I. LYGINOPTERIDEAE.

LYGINOPTERIS.

The genus Lyginopteris is selected for the first place in this chapter simply on the ground that we have a fuller knowledge ofnbsp;its morphology than in the case of other types. It is not regardednbsp;as the most primitive member of its class. Lyginopteris may benbsp;described in a few words as a plant having the habit and to a largenbsp;extent the anatomical features of a Fern, but differing from existingnbsp;ferns in the possession of integumented megasporangia or seedsnbsp;and in the power of secondary growth in thickness by means ofnbsp;a cambium in both stem and root. The seed (Lagenostoma)nbsp;agrees with those of recent Cycads and Gnetales more closelynbsp;than with the corresponding organs in Conifers or any other group,nbsp;while the structure of the secondary wood is practically identicalnbsp;with that of Cycads. The microsporangia occur as groups ofnbsp;small bilocular sporangia, or synangia, at the tips of fertile pinnaenbsp;of highly compound fronds.

Nomenclature and Historical Summary. In 1866 E. W. Binney'^ of Manchester published a short description of a small petrifiednbsp;stem from the Lower Coal Measures of Lancashire and named itnbsp;Dadoxylon oldhamium, employing Endlicher’s term Dadoxylonnbsp;which that author substituted for Pinites as previously used bynbsp;Withani^. Three years later Wilhamson® drew attention tonbsp;certain features in which Binney’s type differs from the genusnbsp;Dadoxylon and substituted a new name Dictyoxylon, suggestednbsp;by the reticulate pitting on the walls of the tracheids. In anbsp;1 Binney (66).nbsp;nbsp;nbsp;nbsp;^ Unger (SO) A. p. 378.nbsp;nbsp;nbsp;nbsp;® Williamson (69).

3—2

subsequent paper Williamson^ gave a fuller description of Binney’s species and spoke of it as ‘ one of the most common plants in thenbsp;calcareous nodules of the Lower Coal Measures’ of Lancashirenbsp;and Yorkshire. He connected certain casts of arborescentnbsp;dimensions with Binney’s type on the ground that the surface-features of the casts are such as would be produced, by partiallynbsp;decorticated stems having a hypodermal reticulum of mechanicalnbsp;tissue like that preserved in the small petrified specimen describednbsp;by Binney (fig. 402). Mr Carruthers called Williamson’s attentionnbsp;to a paper by Mr Gourlie^ in which the generic name Lyginodendronnbsp;is instituted for stem-casts identical in surface-features with thenbsp;fossils figured by Williamson. In spite of the much larger dimensions of the reticulum on the casts described by Gourlie as comparednbsp;with that in the outer cortex of Binney’s stem, Williamson concluded that Lyginodendron is ‘undoubtedly an inorganic cast ofnbsp;the prosenchymatous layer of the bark of Dictyoxylond It is butnbsp;fair to add that Williamson was influenced in coming to thisnbsp;conclusion by a discovery by Mr Yield of a piece of a large petrifiednbsp;stem believed to be generically identical with Binney’s type,nbsp;but subsequently referred to a distinct genus®, which was comparable in size with the stems responsible for Gourlie’s Lyginodendron casts. The type-specimen of Gourlie’s Lyginodendronnbsp;iMndsburgii^, from Carboniferous rocks at Stevenston in Ayrshire,nbsp;Scotland, is represented in fig. 401. The convex areas representnbsp;casts of depressions in a reticulum of cortical tissue, originallynbsp;occupied by comparatively delicate cells, which decayed or shrunknbsp;more quickly than the enclosing framework of stronger fibrousnbsp;elements that remained as a prominent reticulum and producednbsp;the depressions bounding the raised portions of the cast. Suchnbsp;a cast would undoubtedly be formed by the stem on which Binneynbsp;founded his species: the radially disposed bands of thick-wallednbsp;cells seen in the outer part of the section (fig. 402) are portionsnbsp;of an irregular anastomosing mechanical system, the reticulatenbsp;arrangement of which is seen in the impression of a rachis of anbsp;Lijginofteris frond shown in fig. 405, E, and indicated in the morenbsp;slender axis reproduced in fig. 404, A,. 6. This reticulate form of

1 Williamson (73) A. nbsp;nbsp;nbsp;^ Gourlie (44).nbsp;nbsp;nbsp;nbsp;* See page 186.

Solms-Laubach (91) A. pp. 8, 217, 218.

cannot be regarded as a safe criterion of botanical affinity. The largest example of Gourlie’s Lyginodendron that has come undernbsp;ttiy notice is an incomplete sandstone cast from Upper Carboni-ferous strata near Harrogate reaching a length of 100 cm. andnbsp;Solms-Laubaoli (91) A. pp. 8, 217, 218.nbsp;nbsp;nbsp;nbsp;2 Vol. n. p. 220.

with convex areas 13 cm. long. A similar cast, 36 cm. broad, has recently been figured by Nathorst^ from the Culm of Spitz-bergen, and from the Upper Devonian of Ellesmere Land thenbsp;same author has described impressions of a cortical reticulumnbsp;under the name Lyginodendron Sverdriipi^. These specimens arenbsp;interesting as pointing to the former occurrence in the Arcticnbsp;regions of stems—probably Lepidodendroid—reaching the dimensions of a fairly large tree. As Potonié® pointed out, Gourlie’snbsp;generic name serves a useful purpose for casts of stems of thenbsp;type shown in fig. 401 that cannot be assigned to a definitenbsp;systematic position. The genus was first used for a specimennbsp;which has nothing to do with the plant usually spoken of asnbsp;Lyginodendron oldhamium (Binney). Though loath to give upnbsp;a name by which Binney’s type has long been known, in spite ofnbsp;its retention in the second volume of this work I feel compellednbsp;so far to conform to the recognised principles governing nomenclature as to adopt Potonie’s generic term Lyginopteris.

Lyginopteris oldhamia (Binney).

i. nbsp;nbsp;nbsp;Stem.

1866. Dadoocylon oldhamium, Binney, Proo. Lit. Phil. Manchester, vol. v. p. 113.

1869. Dictyoxylon oldhamium, Williamson, Monthly Micros. Journ. vol. ii.

p. 66.

1873. nbsp;nbsp;nbsp;Lyginodendron oldhamium, Williamson, Phil. Trans. Roy. Soc. vol.

CLxm. p. 404.

1899. Lyginopteris oldhamia, Potonié, Lehrbuch der Pfianzenpalaeontologie, p. 171.

ii. nbsp;nbsp;nbsp;Leaf.

1828. Sphenopteris Hoeninghausi, Brongniart, Prodrome, p. 51.

1872. Edraxylon, Williamson, Proc. R. Soc. vol. xx. p. 438.

1874. nbsp;nbsp;nbsp;Bachiopteris aspera, Williamson, Phil. Trans. R. Soc. vol. clxiv. p. 684.nbsp;1877. Calymmatotheca Hoeninghausi, Stur, Culm Flora, ii. p. 266.

1905. Crossotheca Hoeninghausi, Kidston, Proc. R. Soc. vol. nxxvi. p. 358.

iii. nbsp;nbsp;nbsp;Seed.

1877. Lagenoatoma, Williamson, Phil. Trans. R. Soc. vol. cnxvii. p. 234. 1903. Lagenostoma Lomaxi, Oliver and Scott, Proc. R. Soc. vol. lxxi. p. 477.

iv. nbsp;nbsp;nbsp;Root.

1876. Kaloxylon Hoolceri, Williamson, Phil. Trans. R. Soc. vol. clxvi. p. 23. ^ Nathorst(14)Pl. VII. fig. 1.nbsp;nbsp;nbsp;nbsp;^ Nathorst(04) B. p. 11.nbsp;nbsp;nbsp;nbsp;® Potonié (99) B. p. 171.

i. Stem.

The petrified stem on which Binney founded the species was first figured by Dr Arber^ from a section in the Binney collectionnbsp;in the Sedgwick Museum, Cambridge: this section (13mm. innbsp;diameter) is reproduced in fig. 402. The most striking featuresnbsp;are; (i) the pith consisting of an unusually large and irregularnbsp;group of dark thick-walled parenchyma, (ii) the broad cylindernbsp;of manoxylic secondary xylem characterised by multiseriatenbsp;medullary rays, (iii) the outer cortex composed of dark radially

r

quot;V

I'lG. 402. Lyginopteris oldhamia. Transverse section of the type-specimen in the Binney Collection, Sedgwick Museum, Cambridge. (After Arber.)

disposed and oblique bands of mechanical tissue separated from one another by partially destroyed and tangentially elongatednbsp;parenchymatous elements. It is this outer cortex that Williamsonnbsp;aptly compared with the Eoman numerals on a clock-face. Innbsp;the perimedullary region and in contact with the inner edge ofnbsp;tbe secondary-xylem cylinder are six strands of primary xylem

1 Arber, E. A. N. (02).

PTERIDOSPERMEAE

representing the xylem halves of collateral bundles separated from the primary phloem strands by the intervening cylindernbsp;of secondary wood. Two of the primary xylem.strands in lateralnbsp;contact are seen in fig. 404, C; the other four occur as separatenbsp;bundles. Each primary xylem strand contains a small group ofnbsp;spirally thickened protoxylem elements (fx) associated with .anbsp;few parenchymatous cells. The large primary tracheids internalnbsp;to the protoxylem are characterised by multiseriate borderednbsp;pits on their walls, while those external to the protoxylem, whichnbsp;are in contact with the innermost secondary tracheids, havenbsp;scalariform pitting. The dark patch s (fig. 404, C) is a portion ofnbsp;the large group of sclerenchymatous cells, shown in figs. 402, 403.nbsp;The perimedullary xylem strands of mesarch structure are thenbsp;lower portions of leaf-traces and, as Scott points out, ‘each ofnbsp;the bundles surrounding the pith is, in fact, a sympodium, composed of the united lower ends of successive adjacent leaf-traces.’nbsp;The larger of the two bundles shown in fig. 404, C, is on the pointnbsp;of passing out to a leaf, while the smaller strand is on its waynbsp;to a higher level before bending outwards through the secondarynbsp;wood. Slightly beyond the middle of the secondary xylem therenbsp;is an arc of narrower tracheids comparable with an incompletenbsp;annual ring. Although zones or arcs of narrow tracheids are notnbsp;uncommon in the wood of Lyginopteris there is no satisfactorynbsp;evidence of regularly recurring seasonal changes. On the outernbsp;face of the secondary wood are a few leaf-trace strands pursuingnbsp;a vertical course in the pericycle region; but the structure andnbsp;behaviour of these bundles are more clearly illustrated in thenbsp;stem reproduced in fig. 403. The tissue between the crushednbsp;phloem and pericycle and the outer cortex (fig. 402) consists ofnbsp;radially compressed parenchyma with scattered secretory cellsnbsp;separated from the more internal tissue by a narrow band ofnbsp;periderm formed by a phellogen in the outer part of the pericycle.

A larger and better preserved stem, 3-7 cm. in diameter, is seen in fig. 403. In this stem the pith of parenchyma and scatterednbsp;sclerenchymatous nests is larger in proportion to the stele thannbsp;in Binney’s type-specimen. From the inner edge of the secondarynbsp;xylem several primary xylem-strands project as rounded wedgesnbsp;or tangentially elongated groups where two traces are laterally

ï'iG. 403. Lyginopteris oUhamia. a—c, foliar bundles; ƒ, decurrent base of petiole; r, r', roots; s, seed (Lagenostoma). (x 3. Kidston Coll. 592, B.)

united in the perimedullary zone. The cylinder of secondary wood is partially interrupted at r by the bending outwards ofnbsp;the stele of an adventitious root cut across transversely as itnbsp;bends down after emerging from the outer cortical region. Innbsp;more or less close association with the outer surface of the secondarynbsp;xylem are four pairs of leaf-trace bundles and one larger tracenbsp;at d containing two widely separated protoxylem strands andnbsp;faced externally with an arc of secondary xylem: this is a leaf-trace which shows by the slight constriction on the outer edgenbsp;of its primary xylem that it is beginning to divide into a pairnbsp;of equal strands. A precisely similar strand is shown on a largernbsp;scale in fig. 404, D. The twin bundles seen at b, fig. 403,nbsp;represent a divided leaf-trace at a slightly higher level than thenbsp;partially severed trace at d, and the arcs of secondary xylemnbsp;are narrower. The appearance of the double leaf-trace at anbsp;still higher level is shown at c: the two strands are farthernbsp;apart and the secondary xylem has almost disappeared, whilenbsp;those at e, nearer their entrance into the leaf-stalk, consist exclusively of primary xylem and phloem. At a the two strands ofnbsp;a leaf-trace, still nearer to the petiole, are inclined towards onenbsp;another preparatory to reunion after reaching the leaf-stalk.nbsp;A slender root is seen in transverse section at r' immediatelynbsp;outside the two leaf-bundles. As Williamson and Scott^ havenbsp;pointed out, there are always five leaf-traces beyond the xylemnbsp;cylinder of a Lyginopteris stem as seen in transverse section, andnbsp;these traces in the pericycle, separated from one another by |nbsp;of the circumference, alternate in position with the lower portionsnbsp;of leaf-traces in the perimedullary region of the same stem. Thenbsp;phyllotaxis is thus seen to be |.

The secondary wood is succeeded by a cambium of normal structure passing gradually into a narrow band of secondarynbsp;phloem which in well-preserved stems is seen to consist of sieve-tubes and parenchyma with medullary rays rather broader thannbsp;those in the xylem. Beyond the phloem is the comparativelynbsp;broad pericycle consisting of parenchyma with nests of scleren-chyma like those in the pith and scattered secretory cells. Innbsp;the outer layers of the pericycle a phellogen was formed at annbsp;1 Williamson and Scott (95).

early stage in tlie growth of the nbsp;nbsp;nbsp;forms a

of secondary tissue, which is regarded a p nbsp;nbsp;nbsp;^

conspicuous feature in nbsp;nbsp;nbsp;f ^hmids outwards to wrap

paratively dark sinuous band where nbsp;nbsp;nbsp;tProiish the

»gt;u,d a, W-tace. m tWr .Imost ve«.l «»quot; nbsp;nbsp;nbsp;J;

perioydic legion (fig. 403). nbsp;nbsp;nbsp;Ameling W-»»'®

close to the crushed secondary phloem o nbsp;nbsp;nbsp;beyond the

in fig. 404, D. All the leaf-traces seen m fig. nbsp;nbsp;nbsp;J

secondary wood are still within the deep-sea ®

Williamson and Scott showed, each leaf-txac nbsp;nbsp;nbsp;lonsth of

the secondary wood remains in the pericyc e zone o nbsp;nbsp;nbsp;Once

five internodes as it very gradually nbsp;nbsp;nbsp;towarL

free from this region the twin bundles bend moie s a P

the petiole. Stated briefly, the history nbsp;nbsp;nbsp;^e

the perimedullary region to the leaf-base is as ®

outer edge of the pith a single trace consis s o

bundle with one protoxylem strand, P nbsp;nbsp;nbsp;the

five internodes and then bends out throug a nbsp;nbsp;nbsp;in...nbsp;nbsp;nbsp;nbsp;from

xylem-cyhuder, and the primary trachei^ nbsp;nbsp;nbsp;trace leaves

the cambium of the stele on their outer face. nbsp;nbsp;nbsp; lt;7 fi» 403

the secondary xylem it bends upwards and, as seen a , nbsp;nbsp;nbsp;. ,

begins to divide into twin bundles. As the trace pass the bisection of the protoxylem and metaxylemnbsp;nbsp;nbsp;nbsp;apnarate

the secondary xylem-arcs are gradually lost uuti e nbsp;nbsp;nbsp;^

strands of each pair are reduced to single mesarch nbsp;nbsp;nbsp;^

wholly of primary tracheids. As the trace bends ontwar nbsp;nbsp;nbsp;j. „„u

the cortex the phloem gradually encircles eac ^ ®^^ , i-until a concentric structure is substituted for the co a position of the conducting tissue. At the same time enbsp;xylem strands divide and occupy a position near t e inne

of the metaxylem. On reaching the petiole or after passm

distance up the axis of the frond, the twin bund es usually form a V-shaped vascular strand (figs. 404,nbsp;nbsp;nbsp;nbsp;,

The single meristele subsequently divides into two equa p preparatory to the bifurcation of the petiole (fig. 406).

The inner cortex, consisting of parenchymatous many secretory cells with an occasional group of sclerenc ymnbsp;elements in place of the abundant nests of this tissue in e pe

A, B. Frond fragments; a, pinnule; b, reticulum of sclerenchyma.

C. nbsp;nbsp;nbsp;portion of stele of the stem reproduced in fag. 402.

D. nbsp;nbsp;nbsp;px, protoxylem; 5, sclerenchyma; leaf-trace close to the edge of the

secondary xylem; p, peridei'm.

E. nbsp;nbsp;nbsp;Petiole; m, meristele.

(A, Kidston Coll. 664 B; B, Camb. Botany School 508; C, Binney Coll. 179; D, B, Camb. Botany School, 93, 159.)

cycle, has been invaded in the stem shown in fig., 403 by numerous rootlets of Stigmaria and Lyginopteris, some of which are seennbsp;interrupting the continuity of the outer cortex. The greaternbsp;¦width of the cortical region at ƒ, fig. 403, is due to the decurrentnbsp;base of a petiole the meristele of which is not included in thenbsp;section. The lighter and broader bands between the cross-sectionsnbsp;of the stereome-network in the outer cortex are occupied by remains of tangentially stretched parenchymatous cells, and beyondnbsp;this zone in a younger stem there are a few layers of parenchymanbsp;forming the superficial tissue, but there appears to be no well-defined epidermal layer.

Young stems have been recognised in which there is very little secondary xylem and phloem: in these the stereome bandsnbsp;m the outer cortex are closer together than in the stretched hypo-dermal tissue of older shoots and the scattered sclerous nests arenbsp;represented by unthickened cells. In addition to young stemsnbsp;Williamson and Scott described a distinct type of small stem innbsp;which the primary xylem forms an almost complete ring^ comparable with the primary xylem of some adult Sigillarian stemsnbsp;(vol. II. p. 220) but distinguished by its mesarch structure and bynbsp;the reticulate pitting of the centripetal xylem.

A characteristic feature of the stem is the occurrence of emergences from the outer cortex which have the structure eithernbsp;of spinous processes, broadly linear or flask-shaped, or of stalkednbsp;glands^. A portion of a glandular emergence is shown in fig. 405, B:nbsp;the group of small cells immediately below the blunt apex is innbsp;this instance still intact though showing signs of disorganisationnbsp;in the centre; but in many cases the secretory tissue has not beennbsp;preserved and the head of the emergence is occupied by a space.nbsp;A single stoma is seen at s in longitudinal section. Furthernbsp;reference to the emergences is made in the description of the leaf.

It occasionally happens that a meristematic layer is formed in the parenchymatous tissue immediately internal to some ofnbsp;the perimedullary xylem strands of a Lyginopteris stem fromnbsp;which either secondary parenchyma is produced or a zone ofnbsp;secondary xylem and phloem, the phloem facing the centre ofnbsp;the pith. An example of such internal xylem was figured by

^ WiUiamson and Scott (95) p. 720. nbsp;nbsp;nbsp;^ 'Williamson (90) PI. xii. fig. 6.

Williamson^ and similar occurrences are more fully dealt with by Williamson and Scott^ who consider that the perimedullarynbsp;cambium may represent an internal extension through a leaf-gapnbsp;of the normal cambial cylinder. In the stem represented in fig.nbsp;403 there are two perimedullary xylem strands to the left of thenbsp;bottom of the V-shaped gap in the secondary xylem-cylinder, r,nbsp;and on the inner face of one of these, as shown in fig. 405, C,nbsp;there is a narrow arc of internal secondary xylem, c, between thenbsp;xylem-strand and the outer edge of one of the sclerous nests.nbsp;The sporadic occurrence of arcs of inversely orientated secondarynbsp;vascular tissue affords an interesting parallel with a similar morphological feature in some recent Dicotyledonous genera suchnbsp;as Tecoma and lodes. As Williamson and Scott point out, thisnbsp;similarity affords ‘a striking warning against the indiscriminatenbsp;use of even conspicuous anatomical characters®.’ While admittingnbsp;the necessity of guarding against the danger of attaching importance to occasional and abnormal characters they may have somenbsp;significance as collateral evidence in comparisons of differentnbsp;types of stems. It is conceivable that these anomalous arcs ofnbsp;secondary tissue on the inner side of the primary xylem strandsnbsp;may, as WorsdelD maintains, be reversions to an ancestral characternbsp;and in this sense comparable with the strands of inverted vascularnbsp;tissue in some recent Cycadean stems. The question of relationship of Lyginofteris and allied types to recent Cycads and thenbsp;Palaeozoic Medulloseae is considered in a later chapter.

In 1902 Lomax® described two branching specimens of Lygin-ofteris, and more recently two others have been discovered at a locality near Bacup in Lancashire which have been thoroughlynbsp;investigated by Miss Brenchley® who constructed models fromnbsp;drawings of serial sections’^. One specimen shows six leaf-basesnbsp;in a length of 4| inches and branches spring from the axils of fivenbsp;of them: some of the branches show secondary ramifications.nbsp;The phyllotaxis of the leaf-bases on a branch is always the reversenbsp;of that on the main stem, a divergence to which no parallel was

1 nbsp;nbsp;nbsp;WilKamson (90) PI. xiii. fig. 3, b.

2 nbsp;nbsp;nbsp;Williamson and Scott (95) PI. xxiii. fig. 8.

* WorsdeU (06) pp. 140 et seq. nbsp;nbsp;nbsp;® Lomax (02).

’ For a description of the method, see Salisbury (13).

those of Davallia {Odontosoria) aculeata?-, a West Indian fern of climbing habit and with the prickles on Hemitelia and othernbsp;recent Cyatheaceous fronds^, while capitate glands, though simplernbsp;than those of Lyginopteris, occur on the leaf-stalks of some recentnbsp;Polypodiaceous species®. The concentric meristele may consist

in the lower part of the petiole of two separate and slightly curved strands like those seen in fig. 404, E, m\ sooner or laternbsp;the two strands unite to form a wide-open V or a W-shapednbsp;bundle with several slightly internal protoxylem groups close tonbsp;the lower edge. The two sections represented in fig. 406, A and

B show the gradual divergence of the two meristeles ^ J as they approach the level where it divides into t-onbsp;a characteristic feature of Sflienofteris Hoen^ngUus^ m nnbsp;fronds. At a lower level than that represented m fig^ 40^^^nbsp;vascular strand of the petiole would have t enbsp;nbsp;nbsp;nbsp;^

figured hy Williamson in one of his earlier memoirs . r , i with scattered secretory sacs and the adjacent tissue onbsp;stalk are occasionally preserved in wonderful per ec 'nbsp;endodermis has been recognised. Sclerous nests are amp;cnbsp;the ground-tissue as are also secretory sacs (figs- 40 ,nbsp;nbsp;nbsp;nbsp;, i'

A small root r has penetrated the parenchyma of t e rac in fig. 40.5, A.

Sfhenopteris HoeninghausiTixongn.^,iou.nAed on mat '

English Coal Measures, was regarded by Williamson as e yy,pv. of Lyginofteris chiefly on the ground of the occurrence onbsp;genees on the axes (figs. 404, A, B) and laminae of t enbsp;nbsp;nbsp;nbsp;,

like those on the petrified stems, and this comparison recei support from the resemblance of the fragments of pinnu es ^nbsp;dated with Lyginopteris and its petioles in the calcareous nnbsp;’¦ Williamson (74) PI. Li. fig. 1.

^ Scott (09) B. fig. 139, p. 375. nbsp;nbsp;nbsp;^nbsp;nbsp;nbsp;nbsp;^ 42.

“ Brongniart (28) A. p. 199, PI. ui. For synonymy, see Kids nbsp;nbsp;nbsp;^

s. Ill

to the leaflets of Brongniart’s type. This identification is supported by subsequent work. The quadripinnate fronds, which attain a considerable size, resemble those of recent species ofnbsp;Davallia and other ferns, but the forking of the rachis and branchesnbsp;of the frond is a striking feature; the pinnae may reach a lengthnbsp;of 15 cm.^ The portion of carbonised rachis shown in fig. 405, E,nbsp;reveals the existence of a hypodermal reticulum like that in thenbsp;outer cortex of a Lyginofteris stem and the same feature is seennbsp;in the more slender axis represented in fig. 404, A, at 6.^ Thenbsp;pinnules are usually deeply lobed and the segments may benbsp;comparatively broad and blunt or narrow® (fig. 290, C, vol. ii.nbsp;p. 399; fig. 404, A, a, B; fig. 405, D'). The lamina has a wellnbsp;marked dorsiventral structure: the palisade-tissue next thenbsp;upper surface is separated from the epidermis by small hypo-dermal cells, possibly functioning as a water-storage layer, andnbsp;the central part of the mesophyll consists of loose aerenchyma;nbsp;the veins are collateral as in recent ferns and stomata occur innbsp;the lower epidermis. Emergences are seen both on impressionsnbsp;(fig. 405, D') and on petrified specimens. A striking feature ofnbsp;the pinnules is the rounded surface caused by the revolute edgenbsp;of the lamina as seen in the section reproduced in fig. 404, B.nbsp;This character coupled with the occasional occurrence of groupsnbsp;of short tracheal elements at the termination of the veins denotesnbsp;a tendency to a xerophilous habit.

On the strength of a very close resemblance between Sfhenof-teris Hoeninghausi and Calymmatotheca Stangeri (fig. 408, E, F) —characterised by fertile pinnules bearing stellate groups ofnbsp;small linear valves, regarded by Stur as the open lobes of annbsp;indusium—Zeiller included Brongniart’s type in the genus Calymmatotheca. The resemblance in general habit between the twonbsp;species extends to the presence in their rachises of the Dictyoxylonnbsp;form of cortex^. The view formerly held by some authors thatnbsp;the valve-like appendages to the fertile segments of Calymmatotheca are sporangia is incorrect: a re-examination of Stur’s

1 nbsp;nbsp;nbsp;Zeiller (88) A. p. 82, PI. vi.

2 nbsp;nbsp;nbsp;See also Kidston (06) B, fig. 5, p. 417; Renier (lOq, Pis. 60, 70.nbsp;® Kidston (06) B.

0 Star (77) p. 267, Pis. xxv. xxvi.

remains of a stellate group of cupular segments. An examination of the specimen in Dublin convinced me that there is no satisfactory evidence of the seed-nature of the appearance on thenbsp;rock believed by Johnson to be an elliptical Lagenostoma-YikQnbsp;seed. The actual attachment of the stellate lobes to the pinnae ofnbsp;the frond is not clearly demonstrated.

iii. Microsfomngia.

In 1905 Kidston^ announced the discovery of microsporangia on fronds of Lyginopteris: he described specimens from the Coalnbsp;Measures of Dudley identified by him with Sphenopteris Hoening-hausi showing sterile and fertile pinnae in organic connexion.nbsp;The fertile pinnules (fig. 407, B) are slightly expanded distallynbsp;into an oval limb about 2 mm. long bearing 6 to 7 bilocularnbsp;fusiform microsporangia 3 mm. long and 1-5 mm. broad: in thenbsp;immature condition the sorus is hemispherical, the summit beingnbsp;formed of the incurved apices of the sporangia. At maturitynbsp;the sporangia spread out, the sorus assuming the form of annbsp;epaulet. Fig. 408, H, shows a sorus in transverse section and innbsp;fig. 408, G, the limb and two pendulous sporangia are shown.nbsp;The microspores, 50—70 g in diameter, are studded with numerousnbsp;blunt spines and each spore shows a triradiate ridge. The sectionnbsp;reproduced ¦ in fig. 407, A, from the Coal Measures of Oldham isnbsp;probably a bilocular sporangium of the same type as thosenbsp;described by Kidston from Dudley. Dr Kidston^ describes anbsp;second type of microsporangial sorus as Crossotheca Hughesiananbsp;which agrees closely with C. Hoeninghausi, but the fertile segmentsnbsp;are not associated with any sterile pinnae. The generic namenbsp;Crossotheca, founded by Zeiller® in 1883, was substituted fornbsp;Sphenopteris on the ground that Brongniart’s species S. Hoeninghausi is shown to possess sporangia of the Crossotheca type. Ifnbsp;Kidston’s specific determination is correct, his discovery demonstrates that Lyginopteris fronds bore microsporangia having thenbsp;characters of Crossotheca, a type characteristic of several Carboniferous species belonging both to the form-genera Sphenopterisnbsp;and Pecopteris. Eeference has already been made to the difficultynbsp;of distinguishing between impressions of fronds of the Sphenopteris

53

xxix] nbsp;nbsp;nbsp;lygixoptebideae

HoeningUusi group, a difficulty tliat is nbsp;nbsp;nbsp;not

statementi that the Dudley specimens ot Lrossomec identical in the character of the sterile pinnules with ^nbsp;Hoeninghausi. An examination of Dr Eddston snbsp;me to agree with his determination; but, it maj

Eig. 407. A, B. Crossotheca Hoeninghausi.

C. Pinnule with a sporangium, s.

(A, Kidston CoU. 1277; B, after Kidstou; C, Camb. Botany Schoo .

we any evidence of the association with Lyginofteris ^ Pj,q£ sporangia other than those of the Crossotheca typ •nbsp;Chodat^ believes that certain petrified fragments o pnbsp;occasionally met with in the calcareous nodulesnbsp;8'nd apparently annulate sporangia belong to Lygmoftennbsp;These sporangia appear to be identical with those nam J

p. 49.

Scott Pteridotheca Butterworthp and regarded by him as filicean sporangia that cannot be referred to any known Carboniferousnbsp;genus. The piece of lamina bearing an empty sporangium,nbsp;which may or may not have possessed an annulus, reproducednbsp;in fig. 407, C, occurs in association with the larger specimennbsp;shown in fig. 404, B, and it would seem not unreasonable tonbsp;regard both as parts of the same frond, namely a frond of Lyginop-teris. As Prof. Weiss^ points out, the accurate determination ofnbsp;small pieces of petrified pinnules is exceedingly difficult and withoutnbsp;more decisive evidence we are hardly justified in asserting thatnbsp;the sporangia figured by Chodat and Scott and that shown innbsp;fig. 407 belong to the genus Lyginopteris. Although the availablenbsp;data appear to favour the view generally held that Kidston’snbsp;conclusion is correct additional evidence would be welcome.

Telangium. Reference was made in vol. ii.® to the genus Telangium instituted by Dr Benson for some petrified sporangianbsp;from the Coal Measures regarded by her as the microsporangianbsp;of a Pteridosperm, probabh^ Lyginopteris. The sporangia ofnbsp;Telangium are similar to those of Crossotheca. Scott points outnbsp;that they are borne on a flat disc or lamina ‘quite comparablenbsp;to a fertile pinna of Crossotheca^,' and he concludes that thesenbsp;sporangia are not generically distinct from the impressions onnbsp;which the genus Crossotheca was founded. Kidston® regardsnbsp;Telangium ScotH, Benson, as the microsporangium of a Pteridospermnbsp;though not of Lyginopteris, on the ground that the microsporangianbsp;described by Miss Benson are not attached to a limb and thatnbsp;they have a single loculus in place of the double loculus (fig. 407, A)nbsp;of Crossotheca. The presence of a limb in Telangium recognisednbsp;by Scott removes one of these distinguishing features. Therenbsp;are, however, no adequate reasons for regarding Telangium Scottinbsp;as specifically identical with Crossotheca Hoeninghausi. Thenbsp;synangium of Telangium Scotti, 5 mm. in length, consists of 6—12nbsp;sporangia united basally and opening when ripe by longitudinalnbsp;dehiscence. Pig. 493, E, shows eight sporangia of a synangium innbsp;transverse section: the two sporangia at the lower end of thenbsp;section are less distinct than the others, some are full of spores

2 Weiss, F. E. (12). nbsp;nbsp;nbsp;* Vol. n. p. 532.

® Kidston (06) B.

was the first to recognise as the megaspore-bearing organ of Lyginopteris oldhamia. Its structure has been thoroughly describednbsp;by Oliver and Scottand these authors contribute a judicialnbsp;summary of the evidence on which Lagenostoma and Lyginopterisnbsp;are believed to stand for one and the same plant. The evidencenbsp;is based chiefly on the following considerations: an agreementnbsp;in the structure of the vascular bundles in the investments of thenbsp;seed with those in the leaves of T^yginopteris; the presence innbsp;the outer envelope of the seed of stalked glands identical withnbsp;those on the stems and petioles. The evidence does not as yetnbsp;amount to absolute proof, as the seeds, which occur either withnbsp;or without a stalk, have not been found attached to a Lyginopterisnbsp;frond. But ‘ where vegetative and reproductive organs presentingnbsp;identical structural features, not known to occur in other plants,nbsp;are thus found in close and constant association, the inferencenbsp;that the one belonged to the other appears irresistible.’ Whilenbsp;most botanists believe that a satisfactory case is established therenbsp;are a few^ who refuse to believe in a connexion between Lagenostomanbsp;and Lyginopteris until an actual union has been demonstrated.nbsp;The discovery by Kidston® of seeds attached to pinnae bearingnbsp;Neuropteris pinnules and the demonstration of organic continuitynbsp;between seeds and the pinnules of other Palaeozoic fern-likenbsp;fronds supply abundant confirmatory evidence that leaves nonbsp;doubt as to the occurrence of seeds on modified pinnae of Sphenop-teris Hoeninghausi and of other closely allied fronds which representnbsp;the foliage of different forms of Lyginopteris. In this connexionnbsp;it is pertinent to add that Grand’Eury* has found seeds of thenbsp;Lagenostoma type in close association with impressions of Sphenop-teris Dubuissonis and other leaves of similar habit.

A seed of Lagenostoma Lomaxi reaches a length of 5-5 mm. with a maximum diameter of 4-4 mm.; it is broadly oval or barrellike (fig. 408, C) and when immature was invested by a loosenbsp;irregularly lobed glandular envelope (fig. 408, B) from which thenbsp;seed eventually freed itself by a natural process of abscission. Thenbsp;central body or nucellus, except in the apical region, is concrescentnbsp;with a fairly stout integument or testa (fig. 408, C, ƒ) the outer

1 Oliver and Scott (03); (04). ® Kidston (05*) B.

A'

C A nbsp;nbsp;nbsp;J d rlt;/

ch

408. A, Lagamp;nO’Spermwn Sinclairi, B, hage-nostoma^ restoration. C, Lage.-^ostoTna Lomaxi; c, micropyle; d, space between integument and nucellus; e, cupule; ƒ, integument; ch, chalaza. D, microspores of Lagmostmnanbsp;ovoides. E, E, Calymmatotheca Stangeri. G, H, Grossotheca Hoeninghaiisi.nbsp;H, section of G in line of arrow. (A, after Arber; B, C, E, F, after Oliver;nbsp;D, after Benson; G, H, after Kidston.)

portion of which is characterised by regular longitudinal rows of palisade-like cells comparable with the broad palisade-layernbsp;in the sporocarp of Pilularia. On the exposed surface of thisnbsp;palisade-tissue are small dark structureless pegs^, possibly thenbsp;remains of a mucilaginous layer such as occurs on the seed-coatsnbsp;of some recent Flowering plants. At the base of the nucellusnbsp;the chalazal region, fig. 408, C, ch, is provided with sclerousnbsp;elements and forms a hard investment to the axial vascular strandnbsp;from the pedicel. It is at the base of this chalazal region thatnbsp;the seed is eventually cut off by an absciss-layer. The integumentnbsp;is supplied throughout its length by nine vascular bundles of

endarch, or approximately endarch, structure. The free portion of the integument seen from the outside (fig. 408, B) has the formnbsp;of a fluted cone with a circular opening at its summit. Thenbsp;greater part of this domical apex, as seen in longitudinal sectionnbsp;in fig. 408, C, appears to be hollow, but in the living state the dome,nbsp;or canopy as Williamson called it, was filled with parenchymanbsp;in which the vascular bundles were embedded and, as shown innbsp;the transverse section in fig. 409, the canopy is divided intonbsp;compartments by radial septa which in its basal region are replaced

1 Oliver and Scott (04) PI. x. fig. 28; McLean (12).

by regular and deep furrows on the inner face. Enclosed by the canopy, with its outer surface fluted as the result of the partialnbsp;collapse of the outer 'wall of each compartment due to the decaynbsp;of the filling tissue, is the flask-shaped apex of the nucellus,nbsp;between the apical cone of nucellar parenchyma and the superficial layer is an annular cavity which Williamson^ called thenbsp;lagenostome. The parenchymatous core tapers to a narrownbsp;summit which slightly overtops the integument and is constrictednbsp;at the broad base (fig. 493, A, B; page 311). The bottle-shapednbsp;apical tissue is separated by an annular space, c, fig. 493, B,nbsp;from the limiting layer of the nucellus; this space is the pollen-chamber formed in the living seed by the disorganisation of thenbsp;subepidermal cells of the nucellar apex. The pollen-chamber isnbsp;a feature characteristic of recent cycadean ovules (see p. 6).nbsp;In Lagenostoma the annular form of the pollen-chamber is anbsp;peculiarity distinguishing this type of seed from those of recentnbsp;%mnosperms and most other Palaeozoic seeds. As Oliver says,nbsp;it marks an ‘advance in precision’^ over other forms as the microspores which fall into the chamber are brought direct to the surfacenbsp;of the underlying megaspore and presumably to the archegonianbsp;wfiich, it is reasonable to believe, were disposed m a circle at thenbsp;base of the annular crevice. Microspores frequently occur mnbsp;tfie pollen-chamber and some have been discovered apparentlynbsp;lU the act of liberating male gametes®.

outer wall of the nucellus is bounded externally by a

is clearly seen: its surface-layer consists of small cells succeeded by a broad band of radially elongated elements closely resemblingnbsp;the alveoli in the prothalli of some recent Gymnosperms, particularly certain Conifers. No archegonia have been discovered.nbsp;The cupular envelope of immature seeds, compared by Olivernbsp;and Scott with the lobed and glandular husk of Oorylus colurnanbsp;L.^, receives several vascular bundles of collateral and mesarchnbsp;structure from the axial strand, and these subdivide as theynbsp;ascend. The glands which occur on all parts of the cupule arenbsp;sessile or stalked and identical with those on the vegetative organsnbsp;of Lyginopteris. Assuming that pollination occurred at a comparatively early stage in the development of the seed when thenbsp;cupule was still intact, it is conceivable, as Sir Joseph Hookernbsp;suggested, that the glandular secretion may have attracted insectsnbsp;and so aided in the transport of pollen which were perhaps drawnnbsp;down the narrow pollen-chamber by exuded mucilage as in recentnbsp;Conifers. The evidence obtained in recent years in favour ofnbsp;insect-pollination in certain Cycads and in Welwitschia lendsnbsp;support to this view: the dragon flies hovering over a fertilenbsp;Lyginopteris frond in a recent restoration^ may be a legitimatenbsp;addition.

A striking feature of Lagenostoma as of other Palaeozoic seeds is the absence of an embryo; this and other considerationsnbsp;have led certain authors, notably Chodat®, to question the justification for the use of the term seed. Various suggestions havenbsp;been offered in explanation of this fact. In recent Cycads, asnbsp;already pointed out, the development of the embryo does notnbsp;always occur before seed-fall. It may be that these older seedsnbsp;had no resting-period or there may have been a period of restnbsp;after fertilisation and not as now at a stage subsequent to thenbsp;formation of the embryo^; it is also suggested by Scott thatnbsp;‘the nursing of the embryo had not yet come to be one of thenbsp;functions of the seed, and that the whole embryonic developmentnbsp;was relegated to the germination stage®.’ In this connexion

1 nbsp;nbsp;nbsp;Bor figure, see Lotsy (09) p. 714.

2 nbsp;nbsp;nbsp;Scott (11) p. 105.

3 nbsp;nbsp;nbsp;Chodat (08) B.nbsp;nbsp;nbsp;nbsp;i Scott (03).

® Scott (09) B. p. 220. See also Ofiver (05); Oliver and Scott (04) p. 231.

erence may be made to a statement by Miss Gribbs^ who speaks o seeds of a Podocarpus picked up from the ground in apparentlynbsp;mature state and with the associated bracts coloured and swollennbsp;O'S though ready to aid in dispersal but with no embryo: thenbsp;s had matured before fertilisation and fell from the tree afternbsp;Po mation. Whatever may be the true explanation of thenbsp;^ sence of embryos this negative character should not be allowednbsp;outweigh the evidence furnished by morphological featuresnbsp;Hh^'^ applicability of the term seed. As Prof. Oliver says,nbsp;®re IS a long chapter in evolution to be deciphered before wenbsp;connect...the seed of Lyginodendron wdth the sporangium ofnbsp;Th™ PJ’^sent known to us’^.

oute ^ nbsp;nbsp;nbsp;of Lagenostoma has been homologised with the

of the integument of a recent cycadean seed® which, havnbsp;nbsp;nbsp;nbsp;consists of an inner and an outer envelope that

anoth nbsp;nbsp;nbsp;concrescent, and this hypothesis is supported by

Gn author by a comparison between Lagenostoma and ffie coll^^ ®6eds^. A comparison has also been made betweennbsp;of 7°nbsp;nbsp;nbsp;nbsp;^ Ginkgo seed and the much more conspicuous cupule

com nbsp;nbsp;nbsp;Dr Benson and Miss Welsford® institute a

of the^^**^'^ between the vascular supply of the outer integument Laa ^nbsp;nbsp;nbsp;nbsp;°f Carpinus and Morus and that of the cupule of

on the ¦ nbsp;nbsp;nbsp;^ comparison suggested by Miss Kershaw’s remarks^

Mv ¦ ^ nbsp;nbsp;nbsp;between the vascular system of the ovules of

some * nbsp;nbsp;nbsp;^'^'igonocarpus. In 1908 Dr Benson® described

®pecie^^^T^^^^^^^ niicrospores in the pollen-chamber of another believed ° ^^S^^ostoma, L. ovoides, and recognised what shenbsp;for all^nbsp;nbsp;nbsp;nbsp;antherozoids. I am indebted to this author

Two nbsp;nbsp;nbsp;f® make a drawing from her section (fig. 408, D).

holes nbsp;nbsp;nbsp;^^0 ®6en with thick outer wmlls showing irregular

reticul^^*^ nbsp;nbsp;nbsp;secondary origin and not part of a regular

is a h'^^' Benson suggests. Close to the upper microspore np erical body, s, described as a male gamete, and a

^ Gibbs (12) p. 46. f opes (05); Prankerd (12).

^ykes (10) p. 219; Thoday (Sykes, M. G.) (11) p. bhaw (08).

^ Benson and Welsford (09) p. 633.

JSershaw (09) p. 359.

similar body is seen still enclosed by the lower microspore. It is by no means improbable that these are antherozoids: theynbsp;were presumably ciliate like those of Ginkgo and recent Cycadsnbsp;(fig. 396, M). The microspores are approximately 70 in lengthnbsp;and the supposed antherozoids have a maximum diameter ofnbsp;45 fjL, the latter being about | the size of the sperms of Microcycasnbsp;and g the diameter of those of Zamia. The smaller and morenbsp;delicate cells near the lower microspore (fig. 408, D) are no doubtnbsp;fungal cells as Miss Benson suggests. With reference to thenbsp;difficulty of determining the nature of Miss Benson’s supposednbsp;gametes it is worth calling attention to some figures given bynbsp;Zopf^ of vesicular cells and sporangia of the Phycomycetousnbsp;genera Rhizophidium and Lagenidium in the pollen of Floweringnbsp;plants and Pines. It has been suggested by Burlingame^ thatnbsp;the ‘gametes’ may be prothallial cells ; but this is very improbable.

Lagenostoma ovoides Williamson.

In the memoir in which the genus was founded Williamson described two species from the Lower Coal Measures of Lancashire,nbsp;Lagenostoma ovoides and L. physoides^. The seeds described undernbsp;the latter name had previously been assigned by him to anothernbsp;new genus, Physostoma, and named P. elegans*. Lagenostomanbsp;physoides was afterwards figured by Butterworth® who recognisednbsp;some new features. For this species Prof. Oliver® has adoptednbsp;Williamson’s earlier name, Physostoma elegans. The formernbsp;species, which has recently received exhaustive treatment bynbsp;Miss Prankerd'^, agrees generally in its morphological charactersnbsp;with L. Lomaxi, but differs in the structure of the surface-tissuenbsp;of the integument and in some anatomical features. Moreovernbsp;no cupules have been found and there is ‘very little trace of anbsp;layer of separation’ such as occurs in L. Lomaxi. Over thenbsp;surface of the integument is a layer of prismatic cells, much shorternbsp;and less palisade-like than those in L. Lomaxi, and there are nonenbsp;of the pegs which are a constant feature in that species. There

1 Zopf (92) Pis. I. II. ® Williamson (77) B.nbsp;® Butterworth (97).

’ Prankerd (12).

^re, however, indications that mucilage was poured out by the rupture of the distended cells. Some microspores were foundnbsp;lu the pollen-chamber with an average size of 72 x 53 p; theynbsp;may be as much as 90 p, long. None were observed with sperm-ike contents like those described by Dr Benson. Miss Prankerdnbsp;iscusses the morphology of the integument in relation to thatnbsp;cycadean seeds and makes an instructive comparison betweennbsp;the lagenostome (that is the modified nucellar apex) and suchnbsp;n sporangia as those of Angiopteris, Osmunda, and Schizaea,nbsp;especially the sporangia of Senftenbergia^ with their multiseriate

annulus.

^n interesting feature is shown in the longitudinal section reproduced in fig. 493, A (p. 311). The apex of the nucellarnbsp;eone appears to be composed of thick-walled, dark cells and itnbsp;^®^®^ggested that this may have served as a stopper blocking upnbsp;^ ^ circular orifice of the pollen-chamber (seen below the apexnbsp;een the nucellar cone and the thick surface-layer of thenbsp;nucellus) and serving as a protection to the embryo. A comparablenbsp;’]§'Up of the micropyle occurs in the seeds of Gnetum Gnemon^nbsp;in the beak of cycadean seeds. At the time of pollination.

tke lagenostome, the tip of the nucellar cone may have secreted some sticky substance to which the microspores would adhere.

Prof. Lignier^ has recently described some large megasporangia from the Westphalian Coalfield of Ostrau in Austrian Silesianbsp;which he made the type of a new genus Mittagia, after Herrnbsp;Mittag, Director of Mines. Two sporangia, between 2 and 3 mm.nbsp;in diameter, were found in close association as though belongingnbsp;to a single sorus; one was empty and the other contained fournbsp;megaspores. The structure of the thick wall of the sporangianbsp;is very similar to that of the testa of Lagenostoma Lomax%, butnbsp;it apparently split into two valves. Lignier refers the new type,nbsp;Mittagia seminiformis, to some unknown Palaeozoic group ofnbsp;beterosporous Filicineae, possibly the ancestral stock of thenbsp;Pteridosperms, and he thinks it probable that the sporangianbsp;resembled seeds in their facilities for dispersal. In the structure

Vol. II. p. 364, fig. 270. nbsp;nbsp;nbsp;® Berridge (11).

* Lignier (13*).

64 PTBRIDOSPBRMEABnbsp;[CH.

of the sporangial wall Mittagia also resembles the sporocarp of Püularia.

Seeds presented as impressions, without internal structure, superficially resembling Lagenostoma.

Lagenospermum Nathorst.

This generic name is adopted for seeds represented by casts or impressions agreeing in external features with Lagenostomanbsp;but which on the available evidence cannot be confidentlynbsp;assigned to that genus^. Two types of seed were described bynbsp;Arber^ from the Lower Coal Measures of Scotland as Lagenostomanbsp;Kidstoni and L. Sinclairi: the former has been removed bynbsp;Oliver® to Physostoma and both are included by Arber^ in anbsp;recent paper in the genus Radiospermum. This new generic termnbsp;is proposed by Arber for a number of small sub-cylindrical seedsnbsp;founded on impressions including ‘small seeds which, when thenbsp;structure is preserved, are known as lagenostoma, Physostoma,nbsp;and Conostoma.' The question of nomenclature is invariablynbsp;raised by cases in which impressions resemble in their superficialnbsp;characters genera founded on anatomical characters; the seedsnbsp;originally referred to Lagenostoma Sinclairi afford a good examplenbsp;of this difficulty. Nathorst has recently proposed the genericnbsp;name Lagenospermum as preferable to Lagenostoma and Radiospermum in the case of Lagenostoma Sinclairi and similar seedsnbsp;which afford no proof of the possession of such morphologicalnbsp;characters as would justify their inclusion in the genus Lagenostomanbsp;but which may be examples of that genus. As Nathorst pointsnbsp;out, the adoption of Radiospermum for L. Sinclairi is inadvisablenbsp;on the ground that it is also applied to seeds of a different type.nbsp;The type-species of Lagenospermum is L. Sinclairi and Nathorst'nbsp;describes additional species from Lower Carboniferous rocks innbsp;Spitzbergen.

Lagenospermum Sinclairi (Arber ex Kidston ms.).

Although it is not certain that these seeds are morphologically identical with the genus Lagenostoma, a brief description is inter-

XXIX] LAGEXOSPEEMUMnbsp;65

calated here as the habit of the seed-bearing axes supplies a probable key to the habit of the fertile fronds of Lyginofteris. The

gt;~’3 nbsp;nbsp;nbsp;rl d bv Kidston as

Coal Measures of Ayrshire, Scotland, and recor nbsp;nbsp;nbsp;manu-

Lagenostonia sp. •. they were afterwards name nbsp;nbsp;nbsp;-nbsp;nbsp;nbsp;nbsp;, •nbsp;nbsp;nbsp;nbsp;^ppe

script L. Sindairi and handed to Dr Arber ,, ,, „^^etrical seeds are elliptical-oblong, 4-5-5 X 1-5-3nbsp;nbsp;nbsp;nbsp;Jm tibbed and

and enclosed by a loose envelope which is ° nbsp;nbsp;nbsp;4^03^nbsp;nbsp;nbsp;nbsp;A')-

divided distally into several lineai-lanceo a nbsp;nbsp;nbsp;Jj^^enostoma

This covering, though much longer than t P ^ interesting

Lowaxf, is probably a homologous structure. nbsp;nbsp;nbsp;branches of a

point is the attachment of the seeds to nbsp;nbsp;nbsp;„ppds were

compoimd aris (Sg. 408, A). It is

Wne on a frond claracterised by the re uc 1

abortion of the sterile lamina or perhaps, as m (.ojnpound

Thyrsofteris elegans^, some of the pinnae o a g

frond were fertile. It i, worthy of “lt;gt;« .‘“““y, »»lt;«”.

pinnules of Bfhenofteris obtusiloba^ in associa nbsp;nbsp;nbsp;oisnifi-

a fact. » he eaya, in iteeif of no vatae b.t wh.e “^rireloee canr..nbsp;nbsp;nbsp;nbsp;discovery by Carpentier or c i-

ii-xr

y Kidston® from the

canopy formed of the expanded apical free portion of H. pp. 294, 295.

Carpentier (11) p. 3.

Widston (14) p. 160, PI. vn. figs. X, 2.

Ib^d. p. 161^ PI S. II

the integument. The lack of anatomical data in both these seeds is a reason for the substitution of some less committal term thannbsp;Lagenostoma.

Grand’Eury^ and Carpentier^ have published accounts of impressions of seeds from the Coal Measures of France comparednbsp;by them with species of Lagenostoma though not assigned to newnbsp;species. These and similar seeds should be referred to Nathorst’snbsp;genus Lagenospermum.

The difficulty of recognising the true nature of seed-like impressions is illustrated by some specimens in the Goldenbergnbsp;collection in Stockholm described by Arber® as Carpolithusnbsp;Nathorsti: these consist of pieces of Sphenopteris pinnae probably,nbsp;as Zeiller suggested, Sphenopteris Schaumburg-Lippeana (Stur)nbsp;bearing at the ends of the segments of deeply divided pinnulesnbsp;what appeared to be seeds 1 mm. long, oval and longitudinallynbsp;ribbed, and possibly enclosed in a cupide. Arber considerednbsp;the ‘seeds’ to be related to Lagenostoma, probably belonging tonbsp;some member of the Lyginopterideae. An examination of thenbsp;specimens by Nathorst* showed that the supposed seeds arenbsp;collections of spores; but whether the spores of a true Fernnbsp;or the microspores of a Pteridosperm cannot be determined.

Pterispermostrobus Stopes.

Plerispermostrobus bifurcatus Stopes.

Dr Stopes® has recently called attention to a resemblance between specimens from the Westphalian of New Brunswick,nbsp;described by her as Pterispermostrobus bifurcatus, and Lagenospermum Sinclairi. The New Brunswick fossil is made the typenbsp;of a new genus Pterispermostrobus, which is employed for fructifications of Pteridosperms that cannot be associated with a knownnbsp;species of parent and may be either seeds or complex male organsnbsp;borne on a definitely branched rachis. The type-species is represented by a slender axis bearing lateral branches divided intonbsp;two widely divergent arms each of which bears a terminal body,

Grand’Eury (05^) B.

^ Arber, E. A. N. (08).

* Nathorst (08) p. 10, PI. ii. figs. 19—21.

^ Stopes (14) p. 74, Pis. xvii. fig. 45, xxv. fig. 69, text-fig. 15.

XXIX] PTEKISPEEMOSTEOBtTSnbsp;67

4x3 mm., characterised by 3—5 apical lobes extending 2 mm. beyond the distal end of the seed-like organ and resembling anbsp;cupule. In this as in many other cases it is impossible to determinenbsp;the true nature of the reproductive bodies, whether they arenbsp;small seeds or groups of microsporangia: the new generic namenbsp;serves a useful purpose though it is not always possible definitelynbsp;to refer doubtful fructifications of this kind to a Pteridosperm.nbsp;The organs in question may also be compared with Codonotheca^.

Pterispermostrobus pusillus (Nathorst).

The name, Codonotheca pusilla, is given by Nathorst^ to some doubtful specimens from the Culm of Spitzbergen representingnbsp;short stalks bearing linear-lanceolate scale-like bodies, 9—10 mm.nbsp;long by 1 mm. broad, coalescent at the base. Nathorst comparesnbsp;them with Sellard’s species, Codonotheca caduca, but adds that theynbsp;may be cupules of some Pteridosperm and calls attention tonbsp;their resemblance to some fossils figured by Carpentier asnbsp;^olymmatotheca acuta. Both Nathorst’s species and the Frenchnbsp;specimens described by Carpentier® as cupules may be referrednbsp;to Dr Slopes’ genus Pterispermostrobus as their morphologicalnbsp;mature cannot be determined.

V. Roots.

In 1876 Williamson^ described some petrified vegetative organs from the Lower Coal Measures of Lancashire under thenbsp;name Kaloxylon Hooheri characterised by a division of thenbsp;secondary xylem into cuneate masses (fig. 415, C) like those innbsp;some recent Bignoniaceous stems. Williamson at first believednbsp;Kaloxylon to be a stem, but in a later memoir he expressed thenbsp;opinion that ‘it is difficult to believe that these organs have beennbsp;other than roots’®. Felix® had meanwhile described a specimennbsp;from the Coal Measures of Westphalia as Kaloxylon cj. Hooherinbsp;nnd suggested that it might be a waterplant. In 1894 Williamsonnbsp;nnd Scotf^ demonstrated that Kaloxylon Hooheri is the root ofnbsp;Lyginofteris, a conclusion independently reached by Hick®.

^ Nathorst (14) p. 23, PI. sv. fig. 43.

^ Williamson (76) B. ® Williamson (87) p. 297. ' Williamson and Scott (94).nbsp;nbsp;nbsp;nbsp;® Hick (95) p. 114.

5—2

The roots of Lyginopteris arise on all sides of the radially symmetrical stem in the pericycle region; they are copiously branched as is shown by the abundance of roots of various sizes in closenbsp;association. No roots have been discovered exceeding 1 cm. innbsp;diameter nor have any been recorded with secondary periderm-tissue. The absence of root-hairs and the more or less lacunarnbsp;structure of the cortex are indicative of swampy ground. Itnbsp;is seldom that the palaeobotanist has an opportunity of investigating the growing-points of Palaeozoic plants, and for this reasonnbsp;some well-preserved apices of Lyginopteris roots, attributed tonbsp;that genus on the ground of constant association with fragmentsnbsp;of stems in the calcareous nodules of Dulesgate, are of specialnbsp;interest. One of these specimens was figured by Dr Stopes andnbsp;Mr Watson^ in their account of plant-bearing nodules, and a description of that and other examples has since been published bynbsp;Prof. Weiss^. A longitudinal section of a root-tip, -21 mm. innbsp;diameter at its broadest part, shows a root-cap which suggestsnbsp;an origin from a single cell, but an examination of the plerome-cylinder in a slightly tangential section does not afford conclusivenbsp;evidence of the occurrence of a single initial cell. Weiss on thenbsp;whole inclines to the view that Lyginopteris possessed a singlenbsp;apical cell like the roots of Leptosporangiate Ferns, though henbsp;prefers to leave the decision open. Attention is drawn to thenbsp;fact that the plate of tracheidal tissue in emerging lateral rootletsnbsp;is vertical as in Phanerogams and not horizontal as in recentnbsp;Pteridophyta.

The vascular tissue of a Lyginopteris root (fig. 410) consists of from three to eight alternate strands of centripetal xylemnbsp;and phloem, and with the metaxylem is associated a small amountnbsp;of conjunctive parenchyma which does not form a central pith.nbsp;The pericycle, one to several layers broad, is succeeded by annbsp;endodermis which occasionally shows the characteristic thickeningsnbsp;on the radial walls. A broad cortex of thin-walled lacunar tissuenbsp;with numerous secretory cells is bounded externally by a superficial cylinder of two or more layers of comparatively large andnbsp;thin cells, the outermost of which are radially elongated. This

1 nbsp;nbsp;nbsp;Stopes and Watson (08) PI. xvii. fig. 1.

2 nbsp;nbsp;nbsp;Weiss, F. E. (13).

69

LYGINOPTEEIS

ouperficial tissue forms a striking feature by which a Lyginopteris root may often be recognised at a glance. The root representednbsp;in fig. 410, approximately 2 mm. in diameter, has a heptarchnbsp;stele divided into seven xylem-groups by crushed bands ofnbsp;parenchyma and a protoxylem strand occupies the apex of eachnbsp;projecting angle (fig. 410, px). The superficial cylinder of clearnbsp;cells is seen at a. A very small root is seen at r in fig. 410.

r

Pro. 410. Lyginopttris oUhamia. young root, X 30. (Kidston Coll. 403.)

Fig. 415, C, represents part of an older root in which the pent-arch primary xylem is enclosed by broad wedge-like groups of secondary xylem and phloem separated by conspicuous medullarynbsp;rays opposite the protoxylem strands {px). Crushed primarynbsp;phloem arcs, p, are often clearly recognisable beyond the cambium.nbsp;The secondary thickening, as Williamson and Scott state, takesnbsp;place exactly in the manner typical of roots of Dicotyledons,nbsp;so that this fossil might very well be used for purposes of demonnbsp;stration as illustrating the secondary growth of a root withnbsp;diagrammatic clearness’r. The young roots of Lyginopterisnbsp;resemble in many respects those of Marattiaceous Ferns, thoughnbsp;the presence of a single apical cell, if such occurs, is a distinguishing

^ Williamson and Scott (95) p. 739.

feature; but in the presence of secondary conducting tissue they agree with those of Phanerogams.

Distribution of Lyginofteris.

The frequency with which petrified fragments of Lyginofteris stems occur in the calcareous nodules of the English coal seamsnbsp;shows that the genus must have been plentifully represented innbsp;the Upper Carboniferous vegetation, and the occurrence in bothnbsp;North American^ and European localities of fronds identical withnbsp;or closely resembling Sfhenofteris Hoeninghausi affords evidencenbsp;of wide geographical range. Petrified specimens were recordednbsp;by Felix^ from Westphalia in 1886, and Zalessky^ has recentlynbsp;discovered Lyginofteris in the Donetz coal-basin of Russia. Annbsp;investigation by Kubart^ of the calcareous nodules, to whichnbsp;attention was first drawn by Stur, in the Ostrau Coal Measuresnbsp;led to the discovery of several examples of Lyginofteris stems.nbsp;The descriptions and figures so far published are hardly sufficientnbsp;to enable us to estimate the degree of relationship to the Englishnbsp;type, but some of the stems appear to be new species and Kubartnbsp;considers them all to be specifically distinct from Lyginofterisnbsp;oldhamia. Lyginofteris heterangioides contains scattered tracheidsnbsp;in the pith and thus affords an interesting transitional type betweennbsp;Lyginofteris and Heterangium. In L. lacunosum the inner cortexnbsp;is lacunar and the primary xylem bundles pursue an independentnbsp;course in the stele in contrast to the anastomosing arrangementnbsp;in L. oldhamia and in another Hungarian species L. tristichum.nbsp;The species recorded by Kubart occur in the Millstone grit andnbsp;the Coal Measures.

The geological range of Lyginofteris as represented by petrified stems does not extend beyond the limits of the Carboniferousnbsp;system.

HETERANGIUM.

The generic name Heterangium was first used by Corda® for a piece of stem from the Coal Measures of Radnitz, Bohemia,nbsp;represented by part of the vascular axis of a stem consisting

1 White (99) B. p. 40. nbsp;nbsp;nbsp;^ j-elix (86) A.

s Zalessky (10). nbsp;nbsp;nbsp;* Kubart (14); (11).

^ Corda (45) A. PI. xvi.

of strands of large reticulately pitted tracheids intermixed with parenchyma and exhibiting structural features differing apparentlynbsp;from those of any known type. Corda’s material has beennbsp;re-examined by Kubart^ who figures a section from it. Heteran-giiini is a genus closely allied to Lyginopteris both in habit and innbsp;general anatomical characters. The stem is monostelic; thenbsp;Vascular cylinder prior to secondary thickening resembles thenbsp;protostele of certain recent species of Gleichenia and may be compared also with Trichomanes scandens^. It agrees with that *ofnbsp;Lyginopteris in the possession of primary mesarch bundles butnbsp;differs in the substitution of a cauline axial mass of metaxylemnbsp;for the pith of Lyginopteris. The secondary vascular tissue agreesnbsp;closely with that of recent Cycads and Lyginopteris. A characteristic feature is the occurrence of numerous horizontal bands ofnbsp;sclerous cells in the cortex (fig. 412) of the stem and in the ground-tissue of the rachis and larger branches of the fronds. The stemnbsp;quot;quot;^as erect and rarely branched ‘ giving off large foliar appendagesnbsp;^t somewhat distant intervals and from its entire circumferencenbsp;Our knowledge of the reproductive organs is less precise than innbsp;tffe case of Lyginopteris) but we are justified in asserting thatnbsp;^Bterangium is a Pteridosperm which in all probability bore fern-fike microsporangia and seeds similar in general plan to Lageno-

stoma.

The association of some seeds included in Williamson’s genus Lonostoma with Heterangium Grievii in the Pettycur beds andnbsp;their resemblance to Lagenostoma, the seed of Lyginopteris,nbsp;suggested the possibility of actual connexion; further evidencenbsp;in support of this view has recently been brought forward bynbsp;T*r Benson* in the case of a species of Gonostoma which she transfers

a new genus Sphaerostoma.

' Heterangium Grievii Williamson. {Stem.)

'.~y nbsp;nbsp;nbsp;1872. Dictyoxylon Orievii, Williamson, Brit. Ass. Rep. (Edinburgh Meeting),

p. 112.

1873. Heterangium GneTO, Williamson, Phil. Trans. R. Soc. Vol. 162, p. 404.

(Leaf.)

Fumaria officinalis, Volkmann, Silesia subterranea, p. 111, PI. XIV. fig- 2.]

Filicites (Sphenopteris) elegans, Brongniart, Class. Vég. p. 233. Sphenopteris elegans, Brongniart, Hist. Vég. Ross. p. 172.nbsp;Cheilanthites elegans, Goeppert, Eoss. Farnkr. p. 233.

Diplothmema elegans, Stur, Culm Flora, ii. p. 130.

Stem.

At the Edinburgh meeting of the British Association William

gave a brief account of some petrified stems from the Lower

Carboniferous strata of Burntisland on the Firth of Forth which he included in the genus Dictyoxylon. One of these was namednbsp;D. Grievii after Mr Grieve the discoverer of the specimens. Innbsp;.1 later and more complete description Williamson adopted Corda’snbsp;generic name on the ground of the close resemblance of the Scotchnbsp;stem to the Bohemian fragment Heterangium paradoxum. Innbsp;1873^ Williamson added new facts in regard to H. Grievii andnbsp;in 1890® he described a very closely allied type from the Lowernbsp;.Coal Measures of Lancashire. Five years later his descriptionsnbsp;were considerably extended and modified in the joint memoirnbsp;with Dr Scott*.

The great difference in age between the English Upper Carboniferous stem and the Scotch specimens from the Lower Carboniferous beds of Burntisland suggests a probable specificnbsp;, difference. Dr Scott has recently adopted the name Heterangiumnbsp;Lomaxi, proposed but not published by Williamson, for the Englishnbsp;oype. Though in the following account the species Heterangiumnbsp;Grievii is treated in the, broader sense it should be recognised thatnbsp;the geologically younger stem is worthy of specific recognition;nbsp;' it is characterised, to quote Scott®, by ‘the great distinctness ofnbsp;l;he primary xylem strands, by their nearly exarch structure,

¦ nbsp;nbsp;nbsp;* Williamson (72^).nbsp;nbsp;nbsp;nbsp;^ Williamson (73) A.nbsp;nbsp;nbsp;nbsp;® Williamson (90).

* Williamson and Scott (95). nbsp;nbsp;nbsp;® Scott (15).

73

HETBEANGITJM

with little primary centrifugal wood, by the abundant secretory sacs of the stele, and by the rather scattered leaves.’

Heterangium Grievii has a radially symmetrical stem bearing compound leaves with decurrent petioles which give to the otherwise cylindrical axis an angular outline as seen in transversenbsp;section (fig. 411, A). The phyllotaxis appears to be |. The

IXo. 411. Hüerangium Grievii. U, c, leaf-traces; J’’r, root; ph, phloem; x\ primary and secondary xylem, px, proto ynbsp;s, sclerous tissue.

Stem rarely exceeds 1-5 cm. in diameter; in the

paratively large stele consisting in young stems o nbsp;nbsp;nbsp;pvlinder

and phloem, but in older stems these are separated by ^

of secondary vascular tissue which in this species is a nbsp;nbsp;nbsp;,nbsp;nbsp;nbsp;nbsp;.

than in Lyginopteris oldhamia and, as Williamson poi

often of unequal thickness on different radii. The me u a

of Lyginopteris is replaced by a solid xylem-cylinder consisting mainly of groups of large tracheids, reaching -3 mm. in diameter,nbsp;with multiseriate bordered pits (fig. 411, D) embedded in annbsp;anastomosing parenchymatous tissue-system. In the stele reproduced in fig. 411, B, which with the exception of a very narrownbsp;zone of secondary xylem, x^, consists entirely of primary xylem,.

the parenchyma is represented by a darker reticulum {cf..

fig. 415, B) dividing the metaxylem into islands as in Gleichenia. In the peripheral portion of the xylem the tracheids are rathernbsp;narrower and arranged in more definite groups in many of whichnbsp;is a single strand of narrow spiral elements (fig. 411, A', px) closenbsp;to the outer margin. These peripheral primary bundles in whichnbsp;protoxylem is recognisable may be described as leaf-traces ofnbsp;mesarch structure consisting of centripetal xylem and, to a muchnbsp;less extent, of smaller centrifugal elements for the most part withnbsp;. dense spiral bands in place of the multiseriate pits of the rest ofnbsp;the metaxylem. The structure of these leaf-traces is practicallynbsp;identical with that of the primary bundles of Lyginopteris. Therenbsp;is, however, a difference to which attention is drawn by Williamsonnbsp;and Scott. While in Lyginopteris in any transverse section thenbsp;primary bundles in the stele are equal in number to the leaf-traces in the pericycle and cortex, in Heterangium the peripheralnbsp;groups in the stele may be as many as twenty, a number considerably in excess of the leaf-traces beyond the limits of the primarynbsp;xylem of the stele. It may be that the leaf-trace of each leaf,nbsp;which joins the stele at a distance of 6—10 internodes below itsnbsp;entrance into the cortex from the leaf-stalk, may branch in itsnbsp;descent in the axial region, or some of the primary groups ofnbsp;xylem may be confined to the axial region and independent ofnbsp;the leaf-traces. Portions of the peripheral region of the stelenbsp;may be occupied by metaxylem groups without protoxylem andnbsp;identical with those which make up the bulk of the metaxylem.

Scott^ has recently published a note in which he states that most of the British Coal Measures Heterangiums were polydesmic.nbsp;Two bundles, and not a single strand as in the Scotch H. Grievii,nbsp;leave the stele for each leaf, and these divide into four, in somenbsp;cases at least, before entering the petiole.

^ Scott (15).

The secondary xylem is continuous at its inner edge with the outermost primary tracheids (fig. 411, A') and consists of rows ofnbsp;tracheids, 1—3 elements broad, alternating with numerous broadnbsp;medullary rays of radially elongated parenchyma. Beyond anbsp;typical cambium-zone the secondaryphloem consists of parenchymanbsp;and sieve-tubes bounded by crushed arcs of primary phloem.nbsp;Abutting on the phloem is a pericycle composed of several layersnbsp;of small parenchymatous cells (fig. 411, A, p) and in the outernbsp;layers of this tissue a phellogen (fig. 411, C, p) and some peridermnbsp;are usually present though, as Williamson and Scott point out,nbsp;the periderm is less regular and narrower than in Lyginopteris.nbsp;The inner cortex, composed of short parenchymatous cells, isnbsp;traversed by numerous narrow bands of dark, thick-walled cellsnbsp;similar in the structure of the elements, though peculiar in thenbsp;horizontal elongation of the groups, to the sclerous nests in thenbsp;pericycle and pith of Lyginofteris. These characteristic bandsnbsp;are chiefly seen in the oblique longitudinal section of a stemnbsp;represented in fig. 412. In this section, 25 mm. in length, thenbsp;lighter band, p, is the pericycle and in it a few obliquely cut leaf-traces are shown as dark patches. The horizontal bands arenbsp;similar in structure and shape to the diaphragms of thick cellsnbsp;in the pith of Abies magnificat, and in both plants they probablynbsp;serve as supports to the softer parenchyma. There may be asnbsp;many as 46 bands in a vertical length of cortex of 1 inch (aboutnbsp;19 per centimetre). It was the occurrence of precisely similarnbsp;transverse lines on the carbonised impressions of the rachis ofnbsp;Spheno'pteris elegans that led Kidston^ to suggest a connexionnbsp;between that species and the stem of Heterangium Grievii.

The outer cortex, consisting of alternate strands of parenchyma and stereome similar to that of Lyginofteris, is much narrower andnbsp;a less conspicuous feature than in Heterangium', the stereomenbsp;bands do not form so regular a hypodermal network and extendnbsp;touch further vertically without anastomosing. The epidermisnbsp;has been described as a layer of fairly thick cells showing in onenbsp;Case an appearance of a depressed stoma®. There are no secretorynbsp;Canals like those of Cycads but, as in Lyginofteris, scattered cells

t Jeffrey (05) PL in. fig. 21. nbsp;nbsp;nbsp;^ Kidston (91*) B. p. 49.

® Williamson and Scott (95) p. 753.

with dark contents in the stem-tissues probably represent secretory sacs.

The leaf-traces on leaving the stele pursue a very gradually ascending course to the petiole; they retain their collateralnbsp;structure in the pericycle and cortex and have no secondarynbsp;xylem, but become concentric as they enter the base of a leaf.

Before passing to the description of the leaves, the more striking features in the stem may be summarised with reference to thenbsp;diagrammatic sketches shown in fig. 411. Fig. 411, A, representsnbsp;a section of Heterangium Grievii approximately 2 cm. in itsnbsp;maximum diameter; at the periphery of the primary xylem, x^,nbsp;and close to its outer margin are several protoxylem groups,nbsp;not shown in the drawing, each of which marks the position ofnbsp;a mesarch trace. The zone of secondary xylem, x^, is interruptednbsp;bv the exit of leaf-traces and one of these is seen at a in fig. 415, A,nbsp;separated from the central primary xylem by a foliar gap fillednbsp;with parenchyma. The pericycle is shown at p in fig- 412 and

77

Xxix] nbsp;nbsp;nbsp;HBTBRAX6IXJM

its outer boundary at p in fig. dll, Beyond the pericycle is the broad parenchymatous cortex with leaf-traces, U, annbsp;some sclerenchymatous patches, s. The vascular strand a isnbsp;passing into the base of a leaf-stalk. In the stem shown in fig.nbsp;dll, B, 14 cm. X 7 mm., a decurrent petiole is seen at the uppernbsp;end with its single vascular strand, a, and two sclerous nests,nbsp;a similar though detached leaf-base occurs at the opposite end ofnbsp;the long diameter. Other leaf-traces are seen at b and c. Fromnbsp;the left-hand side of the stele a curved strand of tracheids is

passing out to supply a root, r. ii. Root.

Adventitious roots of endogenous origin are occasionally met with in Heterangium stems, but we have less information as tonbsp;their anatomy than in the case of Lyginofteris. In a specimen ofnbsp;Heterangium Lornaxi figured by Williamson and Scott^ three rootsnbsp;are seen in a vertical series growing outwards through the cortexnbsp;of a stem. The roots agree generally with those of Lyginofterisnbsp;but the outermost cortical layers possess no special features.

iii. Leaf.

The iMge compound fronds long known .s were recognised by Kidston ss the leaves o ^nbsp;closely arranged transverse striae or narrnbsp;nbsp;nbsp;nbsp;• t ¦ orirpssions

and pinnae which are the expression on the carbonise nbsp;nbsp;nbsp;stems

of the horizontal plates of sclerous tissue in the petri and petioles of Heterangium. The dichotomously brandiednbsp;are included by Stur in his genus Diflotmema and t anbsp;figures several typical examples in his Culm Flora .nbsp;nbsp;nbsp;nbsp;^ i

shows a forked axis with the bases of more slen er ranc

the characteristic transverse bands and in fig. 413, nbsp;nbsp;nbsp;® rratinn

is reproduced. In general appearance, except in t e i pinnae, the fronds resemble those of DamKanbsp;which Brongniart compared the Palaeozoic species.nbsp;little doubt that S-phenofteris dissecta and some other SPnbsp;were also borne on Heterangium stems. The rachis an p

^ Williamsoii and Scott (95) PI- xxvil, fig- 28.

2 Stur (77) p. 236, Pis. xm. xiv.

difïer from those of Lyginopteris fronds in the absence of emergences (cf. fig. 404, E). The petioles (fig. 411, B, a) have a single concentric vascular bundle with internal protoxylem.

iv. Reproductive organs.

As yet no satisfactory evidence has been published with regard to the nature of the microsporangia but in all probability thesenbsp;were constructed on the same plan as those of Lyginopteris.nbsp;There is a strong prima facie case for assigning the seed Sphaero-stoma to Heterangium: absolute proof of organic connexion isnbsp;still lacking though Dr Benson’s recent account of the seeds

associated with Heterangiuni Grievii almost amounts to demonstration of continuity between vegetative organs and seeds.

^'phaerostoma ovale (Williamson).

In 1877 Williamson described some detached petrified seeds from the Lower Carboniferous rocks of Fifeshire, Scotland, asnbsp;Conostoma ovale and C. intermedium. Dr Benson’s investigation^nbsp;^f these two forms leads her to confirm Williamson’s doubts asnbsp;to the validity of a specific separation and she assigns the single

-m

ï'w. 414. Sphmrostoma ovate. A. Longitudinal section showing the cupule, c, integument, e, ƒ, with vascular bundle, v, the upper part of the nucellus, n,nbsp;and uiegaspore, m; a, archegonia. B. Transverse section through the roofnbsp;of the pollen-chamber, pc, and the summit of the nucellus, n. (After Benson.)

type to the new genus Sphaerostoma. The seeds are always associated with the vegetative organs of Heterangium Grievii.nbsp;In 1909 Oliver^ expressed the opinion that the Burntisland speciesnbsp;of Oonostoma (= Sphaerostoma) is probably the seed of Heterangium.nbsp;The seed consists of a central body representing the nucellus, annbsp;inner integument, and an enveloping cupule or outer integument.nbsp;naost specimens have lost the cupule and in this condition theynbsp;S'le 3-5 mm. long with a maximum breadth of 2-2 mm. In the

^ Oliver (09) p. 111.

middle the seed is circular in transverse section and octagonal near the base and apex. The free apical part of the integumentnbsp;forms a frill (canopy) round the micropyle and extends beyondnbsp;the nucellar apex which consists of a relatively flat plinth surmounted by a central dome or lagenostome (fig. 414). Thenbsp;lagenostome is surrounded by an annular pollen-chamber on tonbsp;the lower surface of which abuts the large embryo-sac, andnbsp;remains of archegonia were noticed below the pollen-chamber.nbsp;The roof of the chamber in the young, state consists of a layer ofnbsp;thin-walled cells extending across the flattened apex of thenbsp;nucellus, n, but as the pollen-chamber becomes differentiatednbsp;from the nucellar tissue by the disorganisation of the zone ofnbsp;cells its roof-cells thicken their vertical walls and assume thenbsp;structure of a multiseriate annulus, which acts as a mechanismnbsp;for opening the pollen-chamber by a circular dehiscence in suchnbsp;a way that the edge of the ruptured roof of the pollen-chambernbsp;slightly overlaps the periphery of the central column of nucellarnbsp;tissue after it has returned to its original position subsequent tonbsp;the entrance of the microspores. The micropylar region is surrounded by eight lobes of the integument and each is characterisednbsp;by a crest of radially elongated cells, fig. 414,/, especially prominent on the outer side. External to this is the slightly longernbsp;cupular sheath (fig. 414, c) which may also have been lobed. Thenbsp;surface of the integument below the terminal crests consists ofnbsp;a layer of cells with small papillae which eventually rupturednbsp;and discharged mucilage. Both integuments have a vascularnbsp;supply, that of the inner integument being represented by eightnbsp;vascular bundles, some of which were found to have mesarchnbsp;xylem, given off from the single strand in the pedicel. Eig. 414nbsp;shows the apical region of a seed of Sfhaerostoma: the flat-toppednbsp;nucellar cap, n, is surrounded by the annular pollen-chamber, pc,nbsp;below which are indicated the archegonia: the wall of the megaspore (embryo-sac) is seen at m and external to this vascularnbsp;bundles, v, run up the inner portion of the integument accompanied by some large cells (aqueous tissue). The elongatednbsp;epidermal cells at the apices of the lobes of the integument formnbsp;the frill,/, and at a lower level the cells of the same layer are muchnbsp;smaller and papillate (e): the outer integument, c, forms the

81

HETEEANGIUM

so-called cupule. The transverse section shown in fig. 414, B, is taken at the level of the roof of the pollen-chamber and ofnbsp;the nucellar cap; it illustrates the contrast between the multi-seriate annulus’ and the central column of small parenchyma.

SpJiaerostonia differs from Lagmostoma in the whorl of crests around the micropyle, in the nearly hemispherical form of thenbsp;lagenostome and in the relatively wider pollen-chamber wrihnbsp;its peculiar form of dehiscence. Miss Benson, while regardingnbsp;Sphaerostoma as similar to Lagenostoma in general plan, believesnbsp;the distinguishing features of the former to be such as are con

sistent with a more primitive form.

An important argument in support of connecting this seed ¦'^ith Heterangium is derived from the juxtaposition of somenbsp;seeds and portions of Heterangium petioles, a juxtaposition thatnbsp;is believed to demonstrate original continuity.

Grand’Eury^ has recorded the association of two species of leaves, Sphenopteris elegans and S. dissecta, with small seedsnbsp;Compared by him with Lagenostoma. In the absence of petrifiednbsp;specimens it would be practically impossible to distinguish betweennbsp;lagenostoma and Conostoma or Sphaerostoma.

Carpentier^ has described some impressions from French Westphalian beds as Conostoma and he records cupules withoutnbsp;seeds on fronds of Sphenopteris obtusifolia which he speaks of asnbsp;having transverse striations like those of Heterangium. Dr Kidstonnbsp;pointed out to me that the surface-features of the Sphenopterisnbsp;i^s-chis are probably due to ramental scales and not to the presencenbsp;of horizontal sclerous bands. Carpentier’s seeds may be comparednbsp;with Lagenospermum Sinclairi.

Heterangium tiliaeoides Williamson, Phil. Trans. R. Soc. Vol. 178, P. 289.

This species, founded by Williamson on material from the Lower Coal Measures of Halifax, Yorkshire, while agreeing innbsp;fhe structure of the primary stele and in the general featuresnbsp;of the cortex with the older Heterangium Grieviiy is clearly dis-finguished by certain well-marked characters. Sclerous groupsnbsp;occur in the inner cortex as in H. Grievii but they are present also

I Grand’Eury (OS^).

S, III

in the pericycle. The peripheral leaf-traces in the stele show the mesarch structure rather more distinctly than in H. Grievii, andnbsp;the secondary xylem, which forms a much broader cylindernbsp;than in the Scotch type, is divided by broad medullary raysnbsp;into characteristic cuneate masses each of which rests at its basenbsp;on the centrifugal tracheids of a leaf-trace strand of xylemnbsp;(fig. 415, B). The most striking distinctive feature is affordednbsp;by the secondary phloem, which is often preserved in wonderfulnbsp;perfection; this is unusually thick and owing to the tangentialnbsp;expansion of the principal medullary rays the secondary phloemnbsp;IS divided into separate masses which decrease in breadth towardsnbsp;the external arcs of primary phloem. The triangular form ofnbsp;the phloem rays, composed of tangentially stretched parenchyma,nbsp;suggested the specific name tiliaeoides on account of their strikingnbsp;resemblance to the rays of Tilia. The leaf-traces are nearlynbsp;always in pairs as they pass out through the cortex; they subsequently divide and appear as four vascular strands in thenbsp;petiole. The portion of stem reproduced in fig. 415, B, 8 mm.nbsp;broad, shows clearly the separation of the secondary xylenj andnbsp;phloem into wedge-shaped groups; in each group there are severalnbsp;Harrow medullary rays. The extrastelar tissues are representednbsp;by a few fragments only. Several layers of crushed peridermnbsp;uccur in the pericyclic region but the more external tissues havenbsp;been almost completely exfoliatedr.

Reference has already been made to Heterangium Lomaxi, the English type originally included by Williamson in Heterangiumnbsp;Grievii. The provisional species Heterangium cylindricum Williamson and Scott^ differs, as Scott says, in no important respect fromnbsp;Lomaxi and should not be retained. A new species, H. mini-Scott®, has been founded on a very small stem from thenbsp;Coal Measures of Dulesgate in which the leaf-traces leave thenbsp;stele as single bundles as in the Scotch H. Grievii.

The French species Heterangium DuchartreH Ren. from Permian rocks was originally referred by Renault to the genus Poroxylon:nbsp;rt is represented by little more than the xylem of the stele and

^ For a fuller description, see Williamson and Scott (95).

, Scott (09) B. p. 410; (15). nbsp;nbsp;nbsp;s goott (15).

Renault (79) B. p. 276, PI. xiv. figs. 4—8; (96) A. p. 251, PI. LXV. figs. 1, 2.

6—2

PTBRIDOSPERMEAE

bears a close resemblance to H. tiliaeoides. Heterangium punctatum Ren. and H. Renaulti^ (Brongn.) also from tbe Permian of Francenbsp;were originally placed in the genus Lycopodium and afterwardsnbsp;recognised as stems of Heterangium. A fourth French Permiannbsp;species, H. bibractense^, is peculiar in the possession of a verynbsp;small primary stele encircled by deep wedges of secondary xylem,nbsp;but without more information it is impossible to speak withnbsp;confidence as to its systematic position. Kubart® has recentlynbsp;published brief descriptions of some stems from the Ostrauernbsp;coal-basin in Moravia all of which he regards as specifically distinctnbsp;from the English types. In Heterangium Sturi the primary xylemnbsp;is almost exarch and the peripheral xylem groups are not verynbsp;clearly defined: in H. alatum, so called from the presence of lateralnbsp;wings on the petioles, the leaf-trace strands are more sharplynbsp;differentiated from the rest of the stele. H. polystichum is anbsp;similar type, and H. Andrei, with a relatively larger amountnbsp;of parenchyma in the stele and thicker stems forms an additionalnbsp;link between Heterangium and Lyginopteris*'. Prof. Johnson® hasnbsp;described a species of Heterangium, H. hibernicum, from Uppernbsp;Devonian and Lower Carboniferous beds in Co. Cork, Ireland, basednbsp;on some impressions of frond fragments without any pinnules. Thenbsp;occurrence of numerous transverse striae on the rachis and lateralnbsp;branches suggests comparison with Heterangium fronds, but an examination of the specimens led me to suspect that some at least ofnbsp;the striae are cracks and not original features. The presence ofnbsp;spur-like appendages from the lower surface of the pinnae near theirnbsp;origin from the rachis is recorded as a peculiar character, and somenbsp;obscure oval bodies, the nature of which is extremely doubtful,nbsp;are considered to be seeds. The imperfection of the materialnbsp;hardly justifies the institution of a new species of Heterangium.

Heterangium ranges from the Lower Carboniferous to the Permian strata and is thus older than Lyginopteris which in thenbsp;form of petrified stems is not recorded from the Lower beds ofnbsp;the Carboniferous system. Heterangium has been described as

1 Renault (96) A. pp. 253, 255. nbsp;nbsp;nbsp;^ Ibid. p. 252, PL Lxv. figs. 3, 6.

* nbsp;nbsp;nbsp;Kubart (14).

* nbsp;nbsp;nbsp;Dr Scott who has seen sections of this species tells me that it is a strikingnbsp;intermediate form.

“ Johnson (12).

having a ‘great preponderance of fern-like characters,’ but having regard to the resemblance of the primary xylem of the latter tonbsp;that of the Osmundaceae it would seem doubtful whether innbsp;their relation to the Ferns there is any important difference.nbsp;Heterangium may safely be spoken of as the more primitive genus.nbsp;The polydesmic character of the petioles of most species is particularly interesting as it brings the genus nearer to the Medulloseaenbsp;and to Rhetinangium'^.

Scott (15),

CHAPTER XXX.

II. MEDULLOSEAE.

The term Medulloseae was first employed by Goeppert and StenzeP for a family of Palaeozoic plants that appears to havenbsp;reached its maximum development in the Permian period: thenbsp;oldest representatives so far discovered are of Upper Carboniferousnbsp;age. Our knowledge of the family is chiefly derived from a studynbsp;of the anatomical characters of stems, and it is therefore on thisnbsp;basis that any grouping of genera or species should be attempted.nbsp;Although there is little information with regard to the reproductivenbsp;organs of Medullosa, the type-genus, it is certain that the Medulloseae are Pteridosperms differing from members of that groupnbsp;included in the Lyginopterideae in the presence of more than onenbsp;stele in the stem, in the habit of the fronds, and in the structurenbsp;of the rachis, as also in the structure of the seeds, though thesenbsp;organs bear a fairly close resemblance to the seeds of Lyginopterisnbsp;and Heterangium. The fronds of the Lyginopterideae are of thenbsp;Sphenopteris type while in the case of such species of Medullosanbsp;as afford evidence of connexion between stems and leaves thenbsp;latter have the characters of Neuropteris, Alethopteris, Odonto-pteris, Linopteris, and other form-genera usually included innbsp;the Neuropterideae. Dr Lotsy^ speaks of Lyginopteris andnbsp;Heterangium as members of the Sphenopteridophylla and assignsnbsp;species of Medullosa either to the Neuropteridophylla or to thenbsp;Pecopteridophylla, the latter subdivision including species withnbsp;fronds of the Alethopteris type. There is, however, little doubtnbsp;that other forms of leaves, such as Odontopteris and possiblynbsp;Taeniopteris, were borne on Medullosan stems. It is undesirable

Goeppert and Stenzel (81).

except in the absence of more trustworthy criteria to make use of so protean a feature as leaf-form as a basis of classification.nbsp;The name Neuropterideae has been frequently employed fornbsp;Pteridosperms other than the Lyginopterideae on the ground thatnbsp;the foliage of Medullosa is represented by species assigned to;nbsp;form-genera included in the Neuropterideae. It is, however,nbsp;preferable to restrict the family-name Neuropterideae to fronds and.nbsp;to speak of the second family of Pteridosperms as the Medulloseae,nbsp;including the genera Medullosa, Sutcliffia, and Rhexoxylon.

MEDULLOSA.

Some species of Medullosa probably resembled in habit Angio-¦pteris evecta and the larger Marattias; they had short and relatively thick stems clothed with the large decurrent bases of long compound fronds superficially like those of some recent Ferns andnbsp;the leaves of the Cycad Bowenia. It is probable that, as Zeiller^^nbsp;has pointed out, the fronds of Medullosa and of other Pteridospermsnbsp;had a greater tendency than those of true Ferns to a dichotomynbsp;of the rachis. In other types the stems reached a considerablenbsp;length and leaves and branches were separated by several feet ofnbsp;bare stem. The large size of the leaf-stalks in proportion to thenbsp;diameter of the stem as shown by such species as Medullosa *nbsp;anglica and M. Leuckarti (fig. 416) suggests either a short andnbsp;thick main axis or, in the case of long stems bearing scatterednbsp;leaves, a plant that supported itself partially at least by a habitnbsp;of growth comparable with that of tropical Aroids or other lianes.nbsp;While Medullosa anglica with its contiguous leaf-bases affordsnbsp;an example of the first type, the occurrence of stems of a Permiannbsp;species, M. stellata, 3| metres long without branches or leaf-scars,nbsp;suggests the habit of a liane; similarly a specimen of Medullosanbsp;Leuckarti in the Chemnitz Museum bearing a few spreading petiolesnbsp;but little narrower than the stem and given off at a wide anglenbsp;Would seem to favour the view that some species were ill adaptednbsp;to be mechanically self-supporting plants. The longest piece ofnbsp;stem that has come under my notice is a specimen of M. stellatanbsp;in the Chemnitz Museum reaching a length of nearly 8 metres:nbsp;some species attained a diameter of about 50 centimetres.

1 Zeiller (05) B. p. 725.

Medullosa is always polystelic: the plan of the vascular system varies considerably as regards both the number and form of thenbsp;steles, but there is a uniform type of structure within the limitsnbsp;of each stele that recalls the single stele of Heterangium. Thenbsp;steles consist of a central region composed of primary xylem,nbsp;originally surrounded by phloem, which in its mesarch or exarchnbsp;structure agrees with the vascular tissue of some species ofnbsp;Gleichenia or Lygodium. To this central region a cambiumnbsp;added secondary xylem and phloem either in the form of a cylindernbsp;of uniform breadth, or more frequently the centrifugally developednbsp;xylem exceeded in amount the secondary conducting tissue addednbsp;to the inner side of the primary region. Apart from anatomicalnbsp;details a Medullosan stem with its several steles, each withnbsp;secondary tissue, embedded in parenchymatous ground-tissuenbsp;resembles the stems of some Dicotyledonous climbers such asnbsp;Thinouia scandens, species of Serjania and Paullinia^.

Anatomically the main features of the stelar system of Medullosa, neglecting the secondary xylem and phloem, are in closer agreement with the stems of Ferns than with those of any othernbsp;plants. It has been shown that the genus Heterangium bearsnbsp;a close resemblance to Gleichenia in the structure of the primarynbsp;stele (fig. 418, C): one of the oldest types of Medullosa, M. anglica,nbsp;may be described as a Heterangium with three steles and may benbsp;compared with a dictyostelic Fern in which the irregular vascularnbsp;framework is made up of three main strands. In certain typesnbsp;of Medullosa (fig. 416) the ground-plan of the vascular systemnbsp;recalls that of a solenostelic Fern, while in others the greaternbsp;complexity suggests comparison with such Ferns as Matonia,nbsp;Angiofteris, Psaronius, or Cyathea', ‘it is as though Nature werenbsp;at the Carboniferous moment in the midst of a series of amazingnbsp;engineering experiments, most of which were either buried deepnbsp;in Palaeozoic oblivion, or permitted to survive only as vestigialnbsp;relics and atavistic ghosts’^. Though many Medullosae resemblenbsp;Ferns there is an important difference between the two groupsnbsp;in the origin of the various plans of Medullosan stelar systems:nbsp;in Ferns the leaf is the determining factor in the evolution ofnbsp;stelar arrangement, while in Medullosa the occasional interruption

1 Schenck (93) B. Pis. i—v, etc. nbsp;nbsp;nbsp;“ White, D. (OS^) B. p. 389.

of a solenostele or the development of an apparently complex dictyostele are features independent of the leaf and leaf-traces.nbsp;In the structure of the secondary xylem and phloem and in root-structure Medullosa agrees with recent Cycads. The genus is innbsp;short a generalised type with filicinean and cycadean affinities.nbsp;In the possession of seeds borne on modified pinnae of compoundnbsp;fronds, Medullosa resembles both Cycas and the Lyginopterideae.nbsp;The seeds exhibit a fairly close agreement with those of Lygino-pteris, Heterangium and recent Cycads, but they appear to havenbsp;advanced further towards the cycadean type than is the casenbsp;with the closely related seeds of the Lyginopterideae. Thenbsp;naicrosporophylls are very imperfectly known but they werenbsp;undoubtedly much less advanced and more fern-like than thenbsp;naegasporophylls.

The genus Medullosa is recorded from the Permian strata of Saxony, France, and Bohemia^; also from the Coal Measuresnbsp;of England, and the discovery of petrified petioles of Myeloxylon,nbsp;the type borne on Medullosan stems in European species, maynbsp;be taken as evidence of the existence of the genus in North Americanbsp;during the Carboniferous period^.

The name Medullosa was applied by Cotta® to three types, Medullosa elegans, M. stellata, and M. porosa, from the Koth-begende of the Chemnitz district. The first of these was recognisednbsp;by Brongniart^ as a distinct genus for which he proposed thenbsp;designation Myeloxylon and this was afterwards identified bynbsp;Renault, Williamson, and other palaeobotanists as a petiole andnbsp;not a stem. Further reference is made to Myeloxylon on a laternbsp;page. Cotta spoke of Medullosa as the most puzzling of thenbsp;genera dealt with in his ‘Dendrolithen,’ and in spite of the manynbsp;additions to our knowledge the position of this Palaeozoic genusnbsp;IS still a fertile source of speculation. The generic designationnbsp;Medullosa is applied to stems, with or without petioles; petiolesnbsp;nr rachises of fronds that frequently occur apart from stems arenbsp;referred to the genus Myeloxylon. The leaves of Medullosanbsp;include several well-known species of Carboniferous and Permiannbsp;genera such as Alethopteris, Neuropteris and others that have in

Solms-Laubacli (97) PI. vi. fig. 3. Cotta (32) B. p. 59.

recent years been transferred from the Filicales to the Pterido-sperms. In a few instances seeds have been found in organic connexion with Medullosean foliage, and there can be no reasonablenbsp;doubt that Trigonocarpus, some forms of Rhabdocarpus, Pachytesta,nbsp;and other seeds represent the integumented megasporangia ofnbsp;Medullosa or some closely allied genus.

Before attempting to summarise the salient features of Medullosa a description of a few selected types will serve to placenbsp;us in a better position to consider the genus as a whole. Thenbsp;British species are placed first on the ground that they are bothnbsp;geologically the oldest though, historically, the most recentlynbsp;described, representatives of the genus; and in the organisationnbsp;of the stem they are simpler than the continental species. Theirnbsp;resemblance to Heterangium serves to some extent to bridge thenbsp;gap between the majority of species of Medullosa and the simplernbsp;types of Pteridosperms represented by Heterangium and Lygino-pteris.

Medullosa anglica Scott^.

Prior to the discovery of this species the genus Medullosa had not been recorded from Britain. A section in the Williamsonnbsp;collection recognised by Scott as that of a Medullosa had beennbsp;identified by Williamson as a large Heterangium stem. Annbsp;undescribed specimen was found by Arber® in the Binney collectionnbsp;at Cambridge which afforded some additional information as tonbsp;the structure of the roots.

The specimens on which Scott’s thorough description is based were obtained by Messrs Wilde and Lomax from the Lower Coalnbsp;Measures of Lancashire. The stem of this oldest species has thenbsp;habit of a tree-fern and is almost completely invested by thenbsp;stout decurrent bases of the petioles of large spirally disposednbsp;compound fronds with a phyllotaxis of |, the leaves of the samenbsp;orthostichy being separated from one another by a vertical distancenbsp;of approximately 10 cm.

A transverse section of a slightly flattened stem is shown in fig. 416, A, the bases of three petioles give to it an angular form.nbsp;Its dimensions are approximately 10 x 4 cm. The ground-tissuenbsp;1 Scott (99).nbsp;nbsp;nbsp;nbsp;2 Arber, E. A. N. (03).

of two of the petioles is continuous with that of the stem, while that of the third leaf-stalk is cut through near its separation fromnbsp;the stem and its adaxial face is already defined by a hypodermalnbsp;band of stereome, d. The surface of the stem is characterisednbsp;by fine longitudinal ribs caused by the slightly projecting stereomenbsp;in the outer cortex, and from the narrow furrows between thenbsp;leaf-bases adventitious roots emerge in vertical series. Thenbsp;position of an interfoliar furrow is shown by a small arrownbsp;in fig. 416, A. There are three steles, 2-3 cm. x 6-10 mm. innbsp;diameter: each agrees very closely in structure with the singlenbsp;stele of Heterangium. Medullosa anglica may be described asnbsp;a polystelic Heterangium and as having the same relation tonbsp;Heterangium as regards the stelar system as Primula auriculanbsp;bears to the monostelic Primula. The central core of the stelenbsp;(the black patches in the diagram, fig. 416, A) consists of annbsp;anastomosing system of tracheal groups embedded in an irregularnbsp;parenchymatous reticulum. The large primary tracheids reachnbsp;a diameter of 150 p. and have multiseriate pitting: at the peripherynbsp;of the primary xylem there is a more definite grouping of tracheidsnbsp;as in Heterangium, and the slightly internal (mesarch) protoxylemnbsp;elements are associated with scalariform and densely spiralnbsp;tracheids (fig. 416, B, C) narrower than the more internal reticulatenbsp;elements. The secondary xylem is manoxylic as in Cycads,nbsp;tracheids in 2-4 radial series alternating with medullary raysnbsp;1-3 cells broad and usually of considerable, depth (fig. 416, B).nbsp;The principal rays are continuous with the parenchymatous matrixnbsp;of the central core. Thick-walled tubular elements, no doubt ofnbsp;the nature of sieve-tubes, form a conspicuous feature in thenbsp;phloem.

The three steles occasionally divide and fuse with one another. The tissue between the steles is crushed and disorganised and innbsp;the living plant was probably small in amount. In the imperfectly preserved inner cortical region there is a sinuous band ofnbsp;secondary parenchyma (periderm; fig. 416, A, c) developed fromnbsp;a deep-seated phellogen; in older stems this formed the superficial tissue after the fall of the leaves. There is no definitenbsp;boundary between the cortex of the stem and the petiole-basesnbsp;except when the hypoderm cuts across the cortex preparatory to

the separation of a leaf-stalk. The stem-cortex and the ground-tissue of the petioles consist of parenchyma with numerous secretory canals, not sacs only as in Heterangium, and arenbsp;abundantly supplied with scattered vascular bundles of collateralnbsp;and exarch structure.

The leaf-traces are furnished by the peripheral tracheal groups at the free surface of the primary portion of each stele: eachnbsp;trace is at first concentric and consists of primary xylem withnbsp;one or more protoxylem strands near the outer surface and isnbsp;completely or partially enclosed by secondary xylem and phloem.nbsp;In the course of its passage to the leaf a leaf-trace loses its secondarynbsp;tissues, which were added by the cambium during the traversenbsp;of the zone of secondary wood, and divides into small collateralnbsp;bundles consisting mainly of spiral and scalariform tracheids.nbsp;The collateral bundles accompanied by some narrow fibres are ofnbsp;the Myeloxylon type (fig. 420), the xylem being wholly centripetal.nbsp;In the behaviour of the leaf-traces and in the vascular systemnbsp;of the petioles Medullosa differs from Heterangium and Lyginofteris.nbsp;Each leaf-base is supplied by sets of vascular strands which passnbsp;into it from the stem at different levels; a large leaf-base reachingnbsp;4 cm. in diameter receives as many as 70-80 bundles. Thenbsp;hypoderm is like that first described in the French species Myeloxylon Landriotii^ and often spoken of as the Sparganum type ofnbsp;hypoderm. The branching of the rachises points to a compoundnbsp;frond, and the occurrence of numerous linear pinnules withnbsp;revolute margins (fig. 420, D) in association with the stem suggestsnbsp;that the ultimate segments were of the Alethopteris form. Thisnbsp;inference receives confirmation from the occurrence of petrifiednbsp;specimens of undoubted Alethopteris rachises with the structure,nbsp;of Myeloxylon. It is practically certain that the leaves bornenbsp;on the stems of Medullosa anglica are those long known asnbsp;Alethopteris lonchitica (Vol. ii. A, p. 553, fig. 364).

An interesting feature in the stems is the occurrence of cortical '''¦ascular strands (fig. 416, A, a, h), reaching a diameter of 7 mm.,nbsp;containing scattered tracheids in a parenchymatous core surroundednbsp;hy secondary xylem and phloem. These cauline bundles arenbsp;almost identical both in structure and distribution with the

^ Renault (76) B.

accessory steles in the stem of a recent Cycas, and the agreement is emphasised by the presence of short square-ended tracheidsnbsp;in the primary xylem.

The roots branch freely and may attain a diameter of more than 1 cm.: they are generally triarch and the triangular primarynbsp;xylem is enclosed by secondary xylem except opposite the proto-xylem. The cortex is like that of Lyginopteris roots and a conspicuous double layer of superficial tissue is another feature commonnbsp;to both {cf. fig. 410). The exceptionally well preserved specimensnbsp;described by Arber^ show very clearly the thick zone of peridermnbsp;which forms the covering of older roots, and in some of the sieve-tubes groups of dark brown patches show the form and arrangement of the sieve-plates.

Refroductive organs. We have as yet no precise information in regard to the reproductive organs of Medullosa anglica, butnbsp;there can be little or no doubt that the fronds bore seeds thatnbsp;have long been known under the generic name of Trigonocarfus.nbsp;Many years ago Mr Hemingway noticed the almost constantnbsp;association of the fronds of Alethopteris lonchitica with Trigonocarfus, and Dr Kidston’s discovery^ of seed-bearing Neurofterisnbsp;pinnae considerably strengthened the evidence derived from merenbsp;association. The structure of Trigonocarfus is described laternbsp;(p. 117) in a section devoted to reproductive organs attributednbsp;to Medullosa. Nothing is known as to the microspore-bearingnbsp;organs.

While in the structure of each of the steles Medullosa anglica agrees very closely with Heterangium, it differs from that genusnbsp;in the presence of three steles and in the structure of the petiolesnbsp;which are much less fern-like than the simpler petioles of Heterangium and Lyginofteris. From the continental species thenbsp;British species is distinguished by its simpler stelar system, thoughnbsp;there is a close correspondence as regards individual steles.

Medullosa fusilla Scott.

This species, briefly referred to by Scott in 1909® and fully described in a recent paper*, is founded on material from the

1 Arber, E. A. N. (03).

® Scott (09) B. p. 441 (footnote).

Lower Coal Measures of Colne, Lancashire. It agrees in essential features with Medullosa anglica, but differs in the following particulars; the linear dimensions of the stem are about one quarternbsp;those of a typical stem of the older species; the leaf-traces possessnbsp;little or no secondary xylem and the relatively large decurrentnbsp;leaf-bases have a narrower and simpler hypoderm. The stemnbsp;has a tri-stelar vascular system enclosed in a ring of internalnbsp;periderm, and each stele (3 mm. in diameter) consists of a roughlynbsp;triangular strand of reticulate tracheids and a small amount ofnbsp;scattered parenchyma. The protox3dem is either exarch or, asnbsp;in M. anglica, niesarch, the exact position being difficult to determine in the available material. The secondary xylem closelynbsp;resembles that of M. anglica.

Scott suggests the possibility that Alethopteris decurrens may be the foliage of Medulhsa fusilla. It is possible that there isnbsp;no specific difference between M. pusilla and M. anglica, butnbsp;on the present evidence the employment of a distinctive namenbsp;is desirable.

Medullosa centrofilis de Fraine.

This species was founded by Miss de Fraine^ on a petrified stem from the Lower Coal Measures of Lancashire. The maximumnbsp;diameter of the flattened stem including four decurrent leaf-basesnbsp;is 5 cm. The vascular system consists of an outer group of fournbsp;steles, reduced to three by fusion in the upper part of the specimen,nbsp;enclosing a central smaller stele or star-ring (fig. 417). It is thenbsp;presence of the star-ring that distinguishes this type from thenbsp;other two British species and forms a connecting link with certainnbsp;continental Medullosae. The peripheral steles agree with thenbsp;steles of M. anglica but, as in M. pusilla, there is some doubt as tonbsp;the exarch or mesarch position of the protoxylem. In the structure of the xylem the central stele conforms to the rest of thenbsp;Vascular system and a strand of protoxylem is preserved that isnbsp;almost certainly exarch. There is evidence that the peripheralnbsp;steles occasionally anastomose, but the central stele follows annbsp;independent course at least in the piece of stem examined. Leaf-traces are furnished by the primary xylem of the outer steles, and

^ De Fraine (14).

they appear to be without secondary tracheids as in M. pusilla. A zone of secondary cortex encloses the vascular system as in thenbsp;other British stems: it is pointed out by Miss de Fraine^ thatnbsp;this tissue, usually described as a deep-seated periderm, mustnbsp;have differed from cork in that there is no sign of drying up ornbsp;decay in the tissues external to it. The leaf-bases are of the usualnbsp;Myeloxylon type. In size this species is intermediate betweennbsp;Medullosa anglica and M. pusilla.

Medullosa stellata Cotta.

Cotta^ described Medullosa stellata as a stem characterised by the occurrence of several many-rayed stellate columns (‘viel-strahlige Sternsaule’) in a pith enclosed by a double cylinder ofnbsp;secondary xylem. The so-called pith is the central ground-tissuenbsp;of the stem and the double ‘striated ring’ of Cotta is a cylindricalnbsp;stele identical in structure with each of the steles of Medullosanbsp;anglica but having a tubular form instead of forming a relativelynbsp;broad and short band [cf. fig. 416, D and A). Goeppert® in hisnbsp;Permian Flora gave a detailed account of the species, some ofnbsp;his sections being cut from Cotta’s material, and by the employment of varietal epithets emphasised the range of variationnbsp;within the limits of the type. Goeppert and StenzeG and, several

1 nbsp;nbsp;nbsp;De F’laine (14) p. 259. See also Kisch (13).

2 nbsp;nbsp;nbsp;Cotta (32) B. p. 66, PI. xiii. The well-preserved specimen figured by Cottanbsp;in his PI. XIII. fig. 2 is in the Dresden Museum.

2 Goeppert (66) A. p. 209, Pis. XL.—xuii.

* Goeppert and Stenzel (81).

years later, Weber and SterzeP adopted the same plan as a convenient method of drawing attention to differences in anatomical characters. As Schenk^ pointed out, there is a considerable risknbsp;in the case of small pieces of stems of attaching excessive importance to structural variations, and it is by no means improbable,nbsp;as he said, that differences which are the expression of statesnbsp;of preservation or stages in development have been incorrectlynbsp;regarded as distinguishing marks of individual plants. It is,nbsp;however, . convenient to recognise some of the more strikingnbsp;deviations from the type-species by speaking of the differentnbsp;forms as varieties though, as Weber and Sterzel fully admit,nbsp;such varieties and even some of the species must be looked uponnbsp;as provisional. Weber and Sterzel give expression to the provisional nature of their grouping by classifying the species withnbsp;their varieties into form-cycles. Under the form-cycle Medullosanbsp;stellata five more or less well defined forms are recognised, thenbsp;type-species being Medullosa stellata var. typica^.

*

Medullosa stellata var. typica.

Part of a transverse section of a cylindrical stem is represented diagrammatically in fig. 416, D. Very little of the cortex is preserved: a parenchymatous axial region with scattered secretorynbsp;canals contains four oval or cylindrical vascular steles, the stellatenbsp;columns of Cotta or star-rings of later authors. These are of thenbsp;same nature as the small central stele in the English Medullosanbsp;centrofilis. The central region of the stem in this specimen isnbsp;Completely surrounded by a narrow cylinder of inversely orientatednbsp;secondary xylem and phloem (fig. 416, D), the phloem being onnbsp;the inner side of the xylem. Beyond the xylem is a parenchymatous band containing scattered groups of primary xylemnbsp;tracheids with spiral, scalariform, and reticulate pitting, andnbsp;this zone, which is usually designated the ‘partial pith,’ isnbsp;succeeded by a second and broader, normally orientated, cylindernbsp;of secondary xylem and phloem. In this section the two concentric cylinders separated by the partial pith form a solenostelenbsp;like that of several recent Ferns except in the presence of secondary

1 Weber and Sterzel (96) B. nbsp;nbsp;nbsp;2 Schenk (89).

* Weber and Sterzel (96) -B. p. 51; Schenk (89).

s. Ill nbsp;nbsp;nbsp;7

tissue. The term ‘partial pith’ applied to the tissue between the two cylinders of secondary tissue is misleading: this tissuenbsp;(fig. 416, D, f) is the primary xylem of the stele and is homologousnbsp;with the primary portion of the stele of Hetemngium and of thenbsp;steles of M. anglica. In many sections the continuity of thenbsp;tubular stele is broken. In a section in the British Museum cutnbsp;from one of Cotta’s specimens^, 6 x 3-5 cm. in diameter to thenbsp;outer edge of the vascular tissue, the cylindrical stele is interruptednbsp;at two places. An example of the interrupted type of stele isnbsp;shown in fig. 416, F, and in fig. 416, H: the latter belongs to anbsp;distinct species. The complete type of cylindrical stele is exceptional and occurs occasionally at different levels in the stem.nbsp;An important point is that the frequent breaks in the cylinder arenbsp;not connected with the exit of leaf-traces and do not, therefore,nbsp;correspond to the foliar gaps in the solenostele or dictyostelenbsp;of a Fern.

The secondary xylem is of the cycadean type (fig. 418, B, D) like that of Heterangium and Lyginofteris and several other stems.nbsp;Each of the star-rings in the axial region consists of a parenchymatous core with scattered primary tracheids enclosed bynbsp;'secondary vascular tissue (fig. 418, B). The star-ring shown innbsp;fig. 418, B, from a Chemnitz stem illustrates the characteristicnbsp;cycadean character of the secondary xylem with broad medullary-rays; some of the innermost elements are in contact with thenbsp;primary tracheids. The phloem is rendered conspicuous by thenbsp;black contents in some of the elements. Both the star-rings andnbsp;the larger peripheral steles are constructed on the same plan andnbsp;agree with the steles of M. anglica. The star-rings occasionallynbsp;branch and anastomose with one another and with the encirclingnbsp;stele. The star-ring in fig. 416, D at a is about to give off a smallnbsp;strand.

Leaf-traces are furnished by the primary xylem at the edge of the ‘partial pith’ of the outer stele: as a leaf-trace passesnbsp;outwards through the outer cylinder of secondary xylem thenbsp;cambium invests it with secondary xylem and phloem, but as itnbsp;passes through the cortex of the stem it becomes reduced to itsnbsp;primary elements, and by successive branching gives rise to

1 No. V. 8093.

small collateral bundles which enter the petioles. The piece of stem shown in fig. 416, Gl, illustrates the exit of leaf-traces fromnbsp;the stele and their subsequent division into several small bundles,nbsp;u, which are scattered in the cortex with strands of sclerenchyma.nbsp;In a specimen identified with MeduUosa stellata, Schenk^ foundnbsp;part of a leaf-base attached to the stem: its vascular system wasnbsp;of the Myeloxylon type, the bundles being identical with thosenbsp;in the cortex of the stem seen in fig. 416, G.

In some stems of M. stellata the outer, centrifugally developed, portion of the main stele is very much broader than in the examplenbsp;represented in fig. 416, D. The diagrammatic sketch reproducednbsp;in fig. 416, F, represents a section of a Chemnitz specimen in thenbsp;British Museum^ in which the axial region containing severalnbsp;star-rings is almost enclosed by an inner zone of secondary xylem,nbsp;and beyond the narrow primary xylem (black in the sketch) thenbsp;rest of the block consists exclusively of secondary xylem 5-5 cm.nbsp;broad. This example illustrates a common tendency in MeduUosanbsp;towards a large excess of centrifugal over centripetal secondarynbsp;vascular tissue. A similar specimen of MeduUosa stellata isnbsp;figured by Mougeot® from the Vosges showing a considerablenbsp;development of centrifugal xylem comparable with that in thenbsp;British Museum stem. Weber and SterzeF describe stems ofnbsp;MeduUosa stellata showing slight periodic swellings which it isnbsp;suggested, though there is no evidence in support of the opinion,nbsp;may be connected with reproductive organs.

MeduUosa stellata var. corticata^. The specimen referred to this variety, represented in fig. 416, G, has already been quoted asnbsp;affording data with regard to the origin and behaviour of the leaf-traces. In this type of stem the outer portion of the main stelenbsp;is narrower than in M. stellata var. typica and the stele never formsnbsp;a complete tube. The star-rings in the centre of the stem arenbsp;more numerous than in the type-species of the genus. In thenbsp;axial region of some stems included in the form-cycle to which

Schenk (82). See also ZeUler (90) B. p. 286.

^ No. 13767, probably identical with M. stellata var. lignosa Weber and Sterzel.

“ Mougeot (52) A. p. 36, PI. iii. figs. 8—10.

* Weber and Sterzel (96) B. p. 108.

^ Ibid. p. 56.

7—2

M. stellata belongs there may be flatter and tangentially elongated vascular strands in addition to the cylindrical star-rings; thesenbsp;are termed plate-rings.

In MeduUosa stellata var. lignosa^ the outer xylem reaches, a breadth of 4 cm. and the star-rings are reduced to one. Thenbsp;form M. stellata var. gigantea^ (fig. 416, K) is of special interestnbsp;as an example of a stem reaching a diameter of nearly 50 cm.nbsp;and having as many as 43 large and small star-rings in the axialnbsp;region. A large tubular stele like that of the type-species (fig-416, D) surrounds the central region, but in this form the cylindrical stole a is succeeded by concentric cylinders of normallynbsp;orientated xylem and phloem (fig. 416, K, bb) produced bynbsp;successive cambiums either cortical or pericyclic in origin. Thisnbsp;type of stem presents a striking resemblance to stems of Cycasnbsp;and Macrozamia except in the possession of a double cylindricalnbsp;stele consisting of both centripetal and centrifugal secondarynbsp;xylem and phloem separated by a zone of primary xylem (partialnbsp;pith).

MeduUosa gigas Renault.

This species was founded on a piece of stem from the Permian of Autun®, consisting almost entirely of secondary xylem, whichnbsp;Brongniart had previously placed in his genus Palaeoxylon*.nbsp;The secondary xylem reaches a diameter of 45—50 cm. and innbsp;the portion of the central region preserved there are a few vascularnbsp;strands like the star-rings of other species. The considerablenbsp;development of secondary xylem indicates a form of stem similarnbsp;to some forms of M. stellata {e.g. fig. 416, F), but as the availablenbsp;data are insufficient for accurate determination Renault’s specificnbsp;name is retained. Renault describes the internal xylem cylindernbsp;(i.e. the centripetal xylem) as very slightly developed or as hardlynbsp;visible, a feature in which the French specimen shows a nearernbsp;approach to the structure of a recent Cycad.

^ Weber and Sterzel (96) B. p. 63. nbsp;nbsp;nbsp;^ Ibid. p. 66.

® Renault (96) A. p. 297; (93) A. PI. lxxi. figs. 1—6.

^ Brongniart (49) A. p. 77.

Medullosa porosa Cotta.

The second of Cotta’s species^, which has been fully investigated by Weber and Sterzel, is constructed on the same plan as that ofnbsp;M. stellata, but the stem is distinguished by the greater numbernbsp;of star-rings and, more especially, by the presence of an outernbsp;system of vascular strands in the axial region (fig. 416, M): thesenbsp;form a frequently interrupted cylinder of anastomosing strandsnbsp;characterised by the feeble development of secondary xylem andnbsp;phloem or by the absence of this tissue on the outer face of thenbsp;strands. The component parts of this outer series occasionallynbsp;fuse with the internal star-rings.

Medullosa Solmsi Schenk^ var. typica Web. and Ster.®

This type has a large axial region containing several very small star-rings enclosed by two concentric zones of separatenbsp;plate-rings (fig. 416, E) each consisting of a complete flattenednbsp;cylinder of secondary xylem and phloem enclosing primary xylem.nbsp;As the complete cylindrical stele of the stem of Medullosa stellatanbsp;shown in fig. 416, D, was compared with the solenostele of anbsp;Eern, so in this stem (fig. 416, E) the vascular cylinder may benbsp;compared at least superficially with a dictyostele. From thenbsp;inner circle of plate-rings strands are given off in the form ofnbsp;star-rings and these pass through the gaps in the outer system,nbsp;eventually breaking up in the cortex into numerous collateralnbsp;bundles. In another form of this species, var. lignosa (fig. 416, L),nbsp;the axial region is enclosed by a circle of plate-rings like thosenbsp;in the type-form, but these are succeeded by a circle of verynbsp;asymmetrically developed and large steles with the outer xylemnbsp;and phloem much broader than the inner. Moreover in thisnbsp;form additional cylinders of normally orientated vascular tissuenbsp;are added as in M. stellata var. gigantea and in some recent Cycads.nbsp;It is noteworthy that the secondary wood of Medullosa Solmsinbsp;IS rather more compact than in other species, anbsp;it to some extent agrees with the South African ;

1 Cotta (32) B. p. 63, PL xii. Bgs. 6, 7

® Schenk (89) p. 339.

® Weber and Sterzel (96) B. p. 541, Pis lii

Bibliotheek

voor aardwetenschappen ^ -dapestlaan 4nbsp;--4 CD Utrecht

Medullosa Leuckarti Goeppert and Stenzel.

In this species also from the Permian of Saxony, the central region including some star-rings is surrounded by sinuous flattenednbsp;concentric steles (snake-rings) agreeing anatomically with thenbsp;steles of other species and characterised by the comparativelynbsp;small breadth of the secondary xylem and phloem (fig;' 416, H).nbsp;Leaf-traces are given off, as in M. anglica and other species, fromnbsp;the outer edge of the primary xylem. In some forms there isnbsp;a single set of snake-rings; in others there is a double series.nbsp;Fig. 418, D, shows part of the secondary xylem of a stele of thisnbsp;species from Chemnitz; the tracheids are in some places continuous with the primary xylem, and on the outer edge of thenbsp;secondary, wood is a cylinder of phloem. A section of Medullosanbsp;Leuckarti figured by Goeppert and StenzeP shows some radialnbsp;rows of very thick-walled elements in the secondary phloemnbsp;which they describe as bast sclerenchyma, but Solms-Laubach®nbsp;believes them to be sieve-tubes. Precisely similar elements arenbsp;figured by Scott^ in M. anglica and as this author suggests the thicknbsp;walls are probably not an original feature. The structure of thenbsp;primary xylem is more clearly seen in fig. 418, C, and the relationnbsp;between primary and secondary xylem is shown in fig. 416, I,nbsp;where the position of the protoxylem may be either exarch ornbsp;mesarch. The protoxylem is only occasionally recognisable butnbsp;some of the peripheral primary tracheal groups are undoubtedlynbsp;mesarch. External to the stele, a part of which is reproduced innbsp;fig. 418, D, are strands of stereome elements and beyond themnbsp;a band of radially elongated cells that may be ‘ periderm ’: stillnbsp;farther out there are some imperfectly preserved vascular bundlesnbsp;that are leaf-traces. This species is important as affording anbsp;complete demonstration of the organic connexion between thenbsp;stem and petioles of the Myeloxylon Landrioti type which indicatenbsp;that the fronds were probably Alethopteroid.

The specimen on which the diagrammatic drawing reproduced

1 Goeppert and Stenzel (81) p. 123, PI. xvi. fi Weber and Sterzel (96) B. p. 79, Pis. iv. v. ix.

^ Goeppert and Stenzel (81) Pi. iii, fig. 15.

* Solms-Laubach (97) p. 179. nbsp;nbsp;nbsp;»

« Scott (99) p. 90.

Fio. 418. A, itfj/ÉÜoxj/iora ro*'a(Mm, part of petiole. B, Medullosa stellata; starring; X 14. C,Tl,MedullosaLenckarti; C, primary xylem; D, part of primary stelar tissues and secondary xylem and phloem; x 6.nbsp;nbsp;nbsp;nbsp;(A—D, Kidston

Coll.. 1014, 1307, 1238.)

in fig. 419 is based has been investigated by Weber and SterzeP and by Solms-Laubach^. The figure is a slightly simplifiednbsp;version of that given by Weber and Sterzel; it represents thenbsp;stem of MeduUosa Leucharti as a transparent object, the twonbsp;lower transverse sections, B andC, being seen in perspective through

the longitudinal faces. The steles are shaded obliquely in the longitudinal sections, and in the three transverse sections, A, B, C,nbsp;the primary xylem (partial pith) is black and the enclosingnbsp;secondary vascular tissue radially shaded. The whole block isnbsp;9 cm. in length and 6 cm. broad. Only a part of the axial regionnbsp;is shown internal to the peripheral snake-rings and in it are thenbsp;star-rings 8, 8, h, and c. Outside the main steles is the narrow

Weber and Sterzel (96) B. p. 95, PI. ix.

cortex R and portions of leaf-bases I—IV. The lowest section, C, shows part of a peripheral snake-ring with a slight swelling atnbsp;ƒ on its inner side which, as seen in sections B and A, foreshadowsnbsp;the separation of the star-ring S and the consequent break innbsp;the continuity of the snake-ring {d, e, sect. B). In section Anbsp;the gap is closed: in the longitudinal section between B and Anbsp;the star-ring S is seen to form two branches, a and b, the branchnbsp;« closing the gap between d and e in section B. These sectionsnbsp;demonstrate the formation of a star-ring from the main peripheralnbsp;stele and the formation of additional star-rings by branching.

l^umerous vascular bundles destined for the leaves are scattered in the cortex. The course of the decurrent leaf-base I is shown on the longitudinal faces, its boundary being marked bynbsp;crowded stereome strands (of the Myeloxylon Landriotii type);nbsp;other leaf-bases are represented by II, III, and 7F.

In habit MeduUosa Leucharti differs from such a type as M. in its relatively shorter and stouter stem and in the shorternbsp;iuternodes.

Leaves and Reproductive Organs.

1- Leaves. It has already been stated that in some cases petioles occur in organic connexion with Medullosan stems,nbsp;ootably in M. anglica and M. Leucharti: in the exceptionallynbsp;Tich collection in the Chemnitz Museum, which forms a fittingnbsp;ïnemorial of the work of the late Prof. Sterzel, there is a stemnbsp;-M. Leucharti bearing large petioles of the type known asnbsp;^ yeloxylon radiatmn. The occurrence of vascular bundles innbsp;c cortex of other species of stem identical with those in thenbsp;attached petioles points to a uniform type of leaf-structure so farnbsp;regards the petioles and rachises of MeduUosa. While it isnbsp;arly unnecessary to distinguish by a special generic title thenbsp;petrified portions of fronds known to belong to certain speciesnbsp;stems, the frequent occurrence of detached petioles necessitatesnbsp;some distinctive term. The name employed is Myeloxylon: thenbsp;genus Was instituted by Brongniart in 1849 for Cotta’s species

Linney m 1872.

Myeloxylon (Medullosan leaf-stalks).

1832. Medullosa elegans Cotta. 1865. Stenzelia Goeppert. 1876. Myelo-pteris Renault^; 1877, Aulacopteris Grand’Eury^.

There is a very close agreement in general anatomical structure between the numerous specimens of Myeloxylon from the Permiannbsp;strata of Saxony and France and the Coal Measures and Millstonenbsp;Grit of England®; the genus is also recorded from the Uppernbsp;Carboniferous of Kansas^. Two well-defined types instituted bynbsp;Kenault are, however, readily distinguished by the form of thenbsp;hypodermal stereome strands. Myeloxylon may be defined asnbsp;follows: Oval or cylindrical branched axes, reaching a diameternbsp;of 15 cm., bearing pinnae having the characters of Alethopteris^nbsp;Neurofteris, Odontofteris, and some other genera that were formerlynbsp;classed as Ferns. Below a single-layered epidermis, in whichnbsp;stomata have been recognised, occur a few layers of parenchyma:nbsp;this superficial tissue, which is rarely preserved, is succeeded bynbsp;a hypodermal region consisting of parenchymatous tissue andnbsp;numerous vertical groups of narrow thick-walled fibres arrangednbsp;as radial plates or circular, oval, or reniform strands (thenbsp;Sfarganum type of cortex). In the hypoderm as in the ground-tissue generally secretory canals, often accompanied by stereome,nbsp;are a characteristic feature. The vascular system is represented bynbsp;a considerable number of collateral bundles scattered throughnbsp;the ground-tissue and especially abundant in the outer region:nbsp;the bundles sometimes assume a more or less regular dispositionnbsp;in concentric circles. Each bundle consists of a small group ofnbsp;xylem tracheids, for the most part spiral or scalariform, thoughnbsp;reticulately pitted elements are by no means rare, with a singlenbsp;protoxylem group on the outer face next the phloem (fig. 420, B, C).nbsp;As a rule the xylem is wholly centripetal, but occasionally thenbsp;exarch structure becomes mesarch by the occurrence of a fewnbsp;centrifugal tracheids. The phloem, rarely preserved (fig. 420, B),nbsp;consists of narrow sieve-tubes with parenchyma, and the bundlenbsp;as a whole is often partially enclosed by a sheath of fibres.

1 nbsp;nbsp;nbsp;Renault (76) B. p. 7.

2 nbsp;nbsp;nbsp;Grand’Eury (77) A. p. 122; (90) A. p. 287:nbsp;^ Seward (93).

Superficially the anatomical structure is similar to that of the petioles of Angiopteris or Marattia, and both Williamson^ andnbsp;Renault placed Myeloxylon in the Ferns; but the collateral formnbsp;of the vascular bundles, the position of the protoxylem, and thenbsp;arrangement of the hypoderm tissues, are cycadean features.

Myeloxylon radiatum (Renault).

This type is characterised by the radially elongated stereome of the hypoderm. Prof. Zeiller^, who has given a very clear and

ooncise description of Myeloxylon, is disposed to regard Cotta’s ^^dullosa elegans as a specifically distinct form on the groundnbsp;that there are two concentric zones of stereome in the hypoderm;

^ Williamson (76) B. p. 8.

but this feature is shown only in one of Cotta’s figures, and Weber and SterzeP point out that a doubhng of the hypoderm zonenbsp;may be caused by accidental juxtaposition of two faulted piecesnbsp;of peripheral tissue. The drawing reproduced in fig. 420, A,nbsp;show’s the structural plan of an unusually large petiole from thenbsp;Permian of Autun: a portion of the outer tissue is seen in fig. 418, A-The vascular bundle, fig. 420, C, from a Millstone Grit specimen^,nbsp;shows the centripetal nature of the xylem and fragments of phloemnbsp;in the outer half of the bundle, with imperfectly preserved fibresnbsp;abutting on the xylem. The characteristic hypoderm is shownnbsp;also in fig. 418, A; the double xylem strand on the left illustratesnbsp;a common feature caused by the branching of vascular bundles.nbsp;Several secretory canals are scattered in the ground-tissue. Thenbsp;pinnules of Myeloxylon mdiatum, or at least of some specimens,nbsp;have been shown by Renault to be of the Neuropteris type.

Myeloxylon Landrioti (Renault)®.

In this species the distinguishing feature is the occurrence of the hypodermal stereome in the form of circular, oval, or reniformnbsp;strands in place of the radial plates of M. radiatum. It is thisnbsp;form of petiole that was borne by the stems of Medullosa anglicanbsp;and M. Leuckarti. In M. anglica the pinnules (fig. 420, D) arenbsp;of the Alethopteris type, almost certainly A. lonchitica. Renaultnbsp;and Zeiller have described French specimens of Myeloxylonnbsp;Landrioti bearing pinnules like those of Alethopteris aquilina andnbsp;A. Grandini.

Myeloxylon topekense (Penhallow).

The occurrence of Myeloxylon petioles in the New' World was recorded by the late Prof. Penhallow’^ who founded thisnbsp;species on some imperfectly petrified specimens from Uppernbsp;Carboniferous strata at Topeka, Kansas. Enough material w’aSnbsp;available to show the Myeloxylon characters, but the preservationnbsp;is too imperfect to admit of a complete diagnosis. The hypodermalnbsp;stereome shows a tendency to form tangentially extended strandsnbsp;in place of the more circular or radially elongated groups in thenbsp;European species.

1 Weber and Sterzel (96) B. p. 102, fig. 26. nbsp;nbsp;nbsp;® Seward (93).

3 Renault (76) B. nbsp;nbsp;nbsp;¦nbsp;nbsp;nbsp;nbsp;*' Penhallow (97

In addition to Akthopteris, Neuropteris (including Cyclopteris) 9^nd Odontopieris fronds, which are known to possess rachises withnbsp;tte Myeloxylon features, there is reason to believe that the Permiannbsp;Collipteris fronds and possibly some of the older Taeniopteris leavesnbsp;Diay also belong to Medullosa^. It is, however, unsafe to assumenbsp;that the occurrence of Myeloxylon petioles necessarily denotesnbsp;the existence of Medullosa. The French stem Colpoxylon aeduensenbsp;Urongn.^ bore leaves with the same general anatomical featuresnbsp;those of a typical Myeloxylon, and there can be little doubtnbsp;that other genera of the Medulloseae also possessed fronds constructed on the same plan as those known to have been bornenbsp;Medullosa. An interesting illustration of an injured organnbsp;that had produced a wound-cambium is afforded by a Myeloxylonnbsp;petiole from the Coal Measures described by Mr Holden®.

^Reproductive Organs.

Reference was made in volume ii. to the reasons which led to the removal of several genera of Carboniferous and Permiannbsp;Ronds from the Filicales to the Pteridosperms, and in Chapter xxix.nbsp;the present volume certain species of Sphenopteris are describednbsp;the foliage of Lyginopteris and Heterangium. It is with suchnbsp;gORera as Neuropteris, Alethopteris, Linopteris and others that wenbsp;now more especially concerned, as they represent some ofnbsp;the types of leaves borne by Medullosa and other members of thenbsp;^ledulloseae. The absence of any specimens among the largenbsp;Eumber of these common genera bearing undoubted sporangianbsp;^-roused suspicion as to the correctness of the generally acceptednbsp;that these fern-like fossils were the leaves of Palaeozoic Ferns.nbsp;Subsequently the suspicion based on negative evidence was con-hïnied by researches into the anatomical structure of the leaf-R’uses, petioles, and fragments of pinnae attached to and associatednbsp;^’dh stems of Medullosa. It is only in a few cases that actualnbsp;'Organic connexion between reproductive organs and Medullosannbsp;Reaves has been demonstrated, but from such facts as are established it is safe to make the general statement that stems ofnbsp;Medullosa—a generic term that undoubtedly includes plants

^ Weber and Sterzel (96) B. p. 139. * Holden, H. S. (10).

which, had we a fuller knowledge of them as complete individuals, would be assigned to more than one generic type—possessednbsp;fronds simulating in habit those of certain Ferns with some ofnbsp;the pinnae bearing seeds often of considerable size and in allnbsp;cases of complex structure, agreeing in many respects with thosenbsp;of existing Cycads, while other fronds, or in some cases it may benbsp;other pinnae, bore microsporangia similar in form to the sporangianbsp;of Ferns.

a. Microsporangia.

Neuropteris. A. Neuropteris Jieterophylla^.

Several examples of supposed fertile specimens of Neuropteris are recorded in palaeobotanical literature, but it was not untilnbsp;1887 that any satisfactory specimen was discovered. In that yearnbsp;Kidston^ described a specimen of Neuropteris heterophylla fromnbsp;the Lower Coal Measures of Scotland in which slender forkednbsp;branchlets bear small bodies at their tips some of which appearnbsp;to represent four-valved organs (fig. 421, D), though the imperfectnbsp;state of preservation renders impossible any definite pronouncement as to their structure. To the specimen are attached a fewnbsp;sterile pinnules, showing that it is a portion of a frond of N. hetero-phylla characterised by the substitution of reproductive organsnbsp;for pinnules. The subsequent discovery of seeds attached tonbsp;pinnae of the same species afforded strong presumptive evidence,nbsp;almost amounting to proof, of the microsporangial nature of thenbsp;Scotch specimen. For this specimen, although no precise diagnosisnbsp;is possible. Dr P. Bertrand® has proposed the generic namenbsp;Neurotheca. In 1911 the Abbé Carpentier* described some smallnbsp;ovoid bodies, 1—1-5 mm. long, from the Coal Measures of Francenbsp;arranged in groups of 4 to 6 and in some cases said to be bornenbsp;on a slender pedicel which he found in association with N. hetero-phylla and compared with sporangia described by Lesquereuxnbsp;from the Coal Measures of Arkansas as Sorocladus stellata^. Thesenbsp;supposed microsporangia have recently been assigned by Bertrand®nbsp;to Sphenophyllum.

1 Vol. II. p. 568, fig. 371.

3 Bertrand, P. (13) p. 117.

^ Lesquereux (80) A. p. 328, PI. XLViii.

B. Neuropteris gigantea, etc. Potoniea, Zeiller.

In 1899 Zeiller’- instituted the name Potoniea for some peculiar fertile leaves found in the Coal Measures of Heraclea consistingnbsp;of a branched axis with cuneate segments, 7—10 x 6—8 mm.,nbsp;hearing numerous fusiform bodies, 1—1-5 mm. long, at the uppernbsp;odge (lig. 421, A). These marginal bodies he regarded as sporangia

A.

B.

C.

D.

E.

(A, C, E, after P. Bertrand; B, after Carpentier; D, after Kidston.)

expressed the opinion that Potoniea may be the fructification of .Q/vw,-. P „nbsp;nbsp;nbsp;nbsp;-nbsp;nbsp;nbsp;nbsp;--

er (99) B. p. 52, PI. iv. fig. 19. nbsp;nbsp;nbsp;^ Carpentier (11) p. 12, Pis xvi. xvil.

from the Pas-de-Calais coal-field as microsporophyll fragments of some Pteridosperm: he stated that similar specimens hadnbsp;been found by Kidston in England. In a later work Carpentier^nbsp;described the sporangia as crowded in groups (fig. 421, B) in thenbsp;substance of the thick lamina of Potoniea, and he connected thenbsp;fertile segments with Neuropteris gigantea, N. pseudogiganteanbsp;Pot. and Linopteris obliqua (Bunb.). Similar specimens are saidnbsp;to have been found in Holland and Silesia. Bertrand^ alsonbsp;records the association of Potoniea with Neuropteris gigantea andnbsp;N. pseudogigantea: he describes some specimens as belonging tonbsp;N. gigantea Sternb. while others, distinguished only by smallnbsp;differences, he attributes to N. pseudogigantea. Kidston® hasnbsp;recently drawn attention to the inconstancy of the charactersnbsp;mentioned by Potonié as distinguishing features of N. pseudogigantea, and he shows good cause for referring the examples sonbsp;named to N. gigantea. The fertile lamina is almost orbicularnbsp;in surface-view and attached to a slightly excentric pedicel; thenbsp;microsporangia are borne on the low^er surface and probably innbsp;groups as described by Carpentier.

Neuropteris Oarpentieri Kidston. Kidston^ has recently described some fertile leaflets under this name from the Westphalian series of South Staffordshire which he identifies with Frenchnbsp;examples referred by Carpentier® to Potoniea adiantiformis Zeill.nbsp;The fertile pinnules are thick and sub-cyclopteroid in form; thenbsp;upper surface bears densely packed, narrow and long, microsporangia, 4 X 0-5 mm., containing more or less spherical microspores 45—60 g in diameter; the ventral face of the lamina onnbsp;the removal of the spores shows several strong veins. Withnbsp;these are associated sterile pinnules of the Neuropteroid type,nbsp;and examples are described intermediate between the sterile andnbsp;fertile leaflets. Kidston believes the specimens to be micro-sporophylls of some species of Neuropteris, but as the materialnbsp;does not suffice for identification with any known species anbsp;new name is proposed. It is pointed out that in some states of

1 Carpentier (13) p. 387, PI. x. figs. 1—6. ‘ Bertrand, P. (13) p. 125.

‘ Ibid. p. 112, PI. viii. figs. 1—7.

® Carpentier (11) p. 13, PI. XVI. fig.1.

preservation the leaflets resemble Goeppert’s Permian species Dictyothalamus Schrollianus^.

Alethopteris. Linopteris.

No specimens of Alethopteris fronds have so far been described that afford any information as to the nature of the microsporangia,nbsp;and we have no means of knowing whether they were borne onnbsp;naked pedicels as in Neuropteris heterophylla, or on modifiednbsp;pinnules as in N. gigantea.

Zeiller in 1888^ described some fertile pinnules of Dictyopteris Schützii Roem. from Commentry bearing two rows of longnbsp;sporangia: he subsequently transferred this species to the genusnbsp;Linopteris^ and expressed the opinion that the sporangia occurnbsp;singly and not in groups as he originally believed. Zeiller comparesnbsp;the fertile pinnules with the type Crossotheca. Bertrand*, asnbsp;the result of examining similar specimens, has suggested thatnbsp;the fringe of pendulous bodies regarded by Zeiller as sporangianbsp;may be tooth-like lobes of modified pinnules which served tonbsp;protect microsporangia borne on the lower surface of the lamina.nbsp;The nature of the impressions is not clear, though there is littlenbsp;doubt that they are microsporophylls. The fertile pinnae ofnbsp;Linopteris obliqua (Bunb.) described by Carpentier® and Bert^hnd®nbsp;closely resemble the microspore-bearing organs which have beennbsp;referred to Neuropteris gigantea) they have the characters ofnbsp;Potoniea and consist of oval laminae similar to the sterile pinnulesnbsp;but about half their size: the lamina was attached excentricallynbsp;to a slender stalk (fig. 421, C, E) and traversed by numerousnbsp;occasionally anastomosing veins. No actual microsporangia havenbsp;been discovered in organic conne.xion with the lamina.

b. Megasporangia.

Neuropteris.

Kidston’s discovery of undoubted seeds attached to pinnae of Neuropteris'^ marked an important step in our more exact

^ See page 127. nbsp;nbsp;nbsp;^ Renault and Zeiller (88) A. p. 273, PI. xxxi. figs. 2, 4.

’ Zeiller (90) B. PI. XI. fig. 9; (00)quot; B. p. 108, fig. 83. See Vol. ii. p. 572.

^ Bertrand, P. (13) p. 132, PI. vi. fig. 7.

^ Carpentier (13) p. 375, PI. vm. fig. 1.

® Bertrand, P. (13) p. 135, pi. vi. figs. 2—4.

’ Kidston (04); (04quot;); (14) p. 107, fig. 5.

S. in nbsp;nbsp;nbsp;8

knowledge of the morphology of Medullosan sporophylls. Specimens from the ironstone balls (Coal Measures) of Coseley near Dudley showed seeds attached to portions of pinnae bearingnbsp;pinnules of Neuropteris heterophylla. The seeds are approximatelynbsp;3 cm. long and from TIO to 1-40 cm. broad; oblong and gradually

Fig. 422. Neuropterocarpus Kidstoni (Arber). (After Kidston; x 3.)

tapering from the middle to a slightly curved and obtuse apical snout (fig. 422). The outer surface shows numerous longitudinalnbsp;ribs which no doubt represent hypodermal fibres. The preservationnbsp;of the seeds, which appear to be circular in section, is not suchnbsp;as to render possible a description of structural features. In theirnbsp;asymmetrical form the seeds agree with the genus Platyspermumnbsp;as recently defined by Arber, but Kidston’s specimens are in allnbsp;probability radiospermic. Kidston compares the Neuropteris seeds

with Rhabdocarpus tunicatus as figured from the Commentry coalfield^ and with specimens from Gard named by Grand’Eurynbsp;-5. subtunicatus^.

Additional proof of the occurrence of seeds on Neuroptens fronds is furnished by examples from the Coal Measures of Hollandnbsp;described by Kidston and Jongmans®; these seeds are of the samenbsp;general type as those from Coseley but nearly twice as large, andnbsp;they were borne at the tips of a dichotomously branched pedicelnbsp;Neuropteris obliqua. Grand’Eury in 1904^ recorded the association of radiospermic seeds with Neuropteris fronds though no casenbsp;of actual attachment was found. It is, however, noteworthynbsp;that he speaks of the frequent association with Neuropteris ofnbsp;Seeds characterised by six or rarely twelve longitudinal keels,nbsp;S' feature recalling the sclerotesta of Trigonocarpus and alliednbsp;seeds. Until petrified specimens are available it is impossible tonbsp;refer the seeds of Neuropteris to a generic type founded on structuralnbsp;features: the seeds described by Kidston are, as he says, verynbsp;similar in external characters to species assigned to Rhabdocarpus,nbsp;^od there can be little doubt as to the generic identity of thenbsp;Neuropteris seeds and some of the impressions referred to Rhabdo-^arpus which are characterised by a similarity in form, an apicalnbsp;Snout that gives an asymmetrical appearance to the specimensnbsp;and the presence of numerous longitudinal striations®. It is,nbsp;however, by no means certain that these seeds possessed thenbsp;]norphological features of Rhabdocarpus as described by Brongniartnbsp;^n petrified examples from St Étienne®.

The seeds of Neuropteris may, as Kidston suggests, agree ana-foinically more closely with P achy tesla'^, a type that Grand’Eury associates with Alethopteris fronds. With a view to avoid thenbsp;Tanger of incorrectly identifying petrified specimens and impressions that cannot be proved to belong to the same genericnbsp;fype, I have suggested the restriction of the name Rhabdocarpus^

to seeds that do not furnish evidence as to internal structure, and the employment of the designation Rhabdospermum for seedsnbsp;that conform to those described by Brongniart as Rhahdocarpus.nbsp;The seeds of Neuropteris may be of the Rhabdospermum typenbsp;or they may agree anatomically more closely with Trigono-carpus or Pachytesta] they are members of either the Trigono-carpales or the Cardiocarpales, probably the former group.nbsp;Dr P. Bertrand^ assigns to Neuropteris gigantea some seedsnbsp;of the Hexapterospermum (= Hexagonocarpus'^) type which occurnbsp;in association with cupule-like organs. These supposed cupulesnbsp;resemble the Potoniea leaflets with microsporangia also referrednbsp;to the same species of Neuropteris-, they are characterised bynbsp;a laciniate edge and may be compared with the Indian fossilnbsp;described by Zeiller as OttoJcaria bengalensis^ (fig. 433). Dr Arber^nbsp;and Dr P. Bertrand® have independently proposed the genericnbsp;name Neurospermum for the seeds of Neuropteris heterophyllanbsp;and N. obliqua in preference to Rhabdocarpus: the former authornbsp;speaks of the seeds of N. heterophylla as Neurospermum Kidstoni.nbsp;The generic term Neuropterocarpus used by Grand’Eury in 1904®,nbsp;though not defined by him, has priority and avoids the adoptionnbsp;of a new designation for seeds attached to Neuropteris fronds.nbsp;In his definition of Neurospermum Arber makes no reference tonbsp;the obliquity of the apical snout that is clearly shown in fig. 422.nbsp;There is no evidence that Neuropterocarpus possessed a cupularnbsp;investment comparable with that of Lagenostoma. Additionalnbsp;instances of the association of seeds with Neuropteris fronds arenbsp;recorded by Renier from the Belgian Coal Measures, also bynbsp;Bertrand and Chodat from France; Renier found seeds associatednbsp;with N. Schlehani Stur and with the same species of frond Bertrandnbsp;found impressions of oval ribbed seeds. Prof. Chodat’ hasnbsp;figured some fragments of Neuropteris pinnules referred to N.nbsp;auriculata Brongn. from the Stephanian of France which shownbsp;small seed-like bodies apparently in organic connexion withnbsp;the lamina; but the specimens are too imperfect to afford any

1 P. Bertrand (13) p. 129, PI. vii. figs. 1, 2, 7. nbsp;nbsp;nbsp;^ See Chapter xxxv.

3 See page 139. nbsp;nbsp;nbsp;^ Arber (14) pp. 93, 103, PI. vm. fig. 47.

P. Bertrand (13) p. 121. nbsp;nbsp;nbsp;« Grand’Eury (04^) p. 78Ö (footnote).

' Chodat (08) B. p. 33, fig. 15.

satisfactory evidence as to the nature of the reproductive organs.

Lotsyi has expressed the opinion that the bodies attached to Neuropteris pinnae described by Kidston and other authors asnbsp;seeds may possibly be vegetative buds, but if this were the casenbsp;one would expect to find some evidence of the bud-nature innbsp;some at least of the specimens that have already been found.

It would seem that the microsporophylls of Neuropteris were constructed on different plans, some being of the type describednbsp;by Zeiller and other observers as Potoniea, while others borenbsp;sporangia on pinnae without any accompanying laminae; but ournbsp;knowledge of the latter form represented by Kidston’s specimennbsp;of Neuropteris heterophylla (fig. 421, D) is very incomplete. Onnbsp;Ike other hand the seeds appear to have been characterised bynbsp;features suggesting a close affinity to Trigonocarpus and pointingnbsp;lo membership of the same family.

¦^lethopteris.

Although no specimens have been discovered showing actual connexion between fronds and seeds, it is practically /certainnbsp;that Alethopteris leaves, or at least some species of the genus,nbsp;tore seeds of the Trigonocarpus type. The association of Trigono-lt;^arpus Parlcinsoni with Alethopteris lonchihca is too frequent tonbsp;he fortuitous and there is further evidence afforded by certainnbsp;anatomical resemblances. In Trance other species of Alethopteris,nbsp;^¦9- Alethopteris Serlii and A. Grandini, occur in association withnbsp;^O'Chytesta^, a large seed similar to Trigonocarpus, and Trigonocarpus is found in the Pas-de-Calais coal-field with Alethopterisnbsp;Serlii,

Trigonocarpus. Brongmart.

The generic name Trigonocarpum was instituted by Brongniart

1828® for ovoid longitudinally ribbed ‘fruits’ from Upper ^arboniferous strata, the type-species being named T. Parkinsoni.nbsp;generic name is often altered to Trigonocarpon; Williamson^,

2 Grand’Eury (04); (04) B.

who adopted this form, states that Brongniart substituted Trigono-carpon for Trigonocarpum in his Tableau?-, but in that work the original termination is used, the form Trigonocarpon, probablynbsp;the result of a slip, appearing only in the index. In his laternbsp;work on seeds Brongniart adopted the name Trigonocatpus, andnbsp;in recent years this has been widely employed. Among othernbsp;species named by Brongniart are two previously referred bynbsp;Sternberg to Palmacites. Several examples of Brongniart’s genusnbsp;were described by Bindley and Hutton, and in their description of T. Noeggeralhii the statement is made that a fracturednbsp;specimen demonstrated that ‘the fossil in its ordinary state is

an interior part divested of fleshy covering’^; this suspicion of the true nature of the nut-like fossils was afterwards provednbsp;correct by the investigations of Hooker and Binney® and by thenbsp;later work of Williamson. The specimens on which the genusnbsp;was founded are casts of seed-cavities and it is in this state thatnbsp;the seeds are usually preserved, often in large numbers, in thenbsp;sandstones of the Coal Measures, as in the block shown in fig. 423nbsp;from the famous quarry at Peel near Bolton, Lancashire. Anothernbsp;type of preservation is represented by the seeds figured by Bindleynbsp;and Hutton as Carpolithes alata^^, but the generic identity of thenbsp;two states was not recognised until the discovery of petrifiednbsp;material afforded the clue. Figs. 424,1, 425 illustrate the appearance of Trigonocarpus when preserved as a carbonised impression

^ Brongniart (49) A. p. 91. nbsp;nbsp;nbsp;^ Bindley and Hutton (35) A. p. 172.

^ Hooker and Binney (55). nbsp;nbsp;nbsp;‘ ^ Bindley and Hutton (33) A. PI. 87.

119

TEIGOXOCARPtrS

showing a thick fleshy envelope enclosing an oval kernel with ^ hard wall prolonged upwards as a longer or shorter micro-Pyle. Casts of the seed-cavity are represented in figs. 423;nbsp;424, 2, 3. The surface of these casts occasionally shows one ornbsp;more short cylindrical projections which are probably extensionsnbsp;of the sand or mud into holes formed in the testa by boring insects.nbsp;The view that Trigonocarpus seeds are ‘obviously Palm fruitsnbsp;'vas not accepted by Hooker and Binney who inclined to regardnbsp;them as the seeds of Conifers and compared them especially withnbsp;the similar nuts of Ginkgo seeds {cf. fig. 631, C). It was Mr Wildnbsp;who was first struck by the association of Tfigonoca/rpus andnbsp;tfie petioles of Medullosa (Myeloxylon) and by some resemblancesnbsp;in structure between the testa and the hypoderm of the petioles;nbsp;though, as Scott and Maslen^ point out, the agreement is not sonbsp;close as Wild believed, his view of a possible connexion betweennbsp;the reproductive and vegetative organs has been confirmed.nbsp;Williamson extended our knowledge of the genus by his accountnbsp;of Trigonocarpus olivaeformis Lind, and Hutt., a form that isnbsp;specifically identical with T. Parkinsoni Brongn. This authornbsp;also drew attention to the close resemblance between BroU^niart snbsp;three genera Trigonocarpus, Hexapterospermum, Tripterospermumnbsp;and expressed doubts as to the possibility of founding spcifionbsp;differences on casts of the Trigonocarpus type without the evidencenbsp;of anatomy. Our knowledge of the structure of Trigonocarpusnbsp;has in recent years been considerably extended by the researchesnbsp;of Oliver, Scott and Maslen, and Salisbury.

TnponocarpMs Parkinsoni^ Brongniart.

The seeds of this species like all examples of the genus are ïadiospermic, that is radially symmetrical in contrast to thenbsp;flattened or platyspermic seeds. The complete seed is elongatenbsp;Oval in form when preserved as an impression (fig. 425, A) andnbsp;reaches a length of 4—5 cm.: the casts of the seed-cavity arenbsp;ovoid and provided with three prominent ridges (fig. 424, 2, 3).nbsp;The testa forms a thick covering differentiated into three regions,nbsp;an outer flesh or sarcotesta, a sclerous shell or sclerotesta, and

^ Wild (00). nbsp;nbsp;nbsp;2 Scott and Maslen (07) p. 96.

^ Scott and Maslen (07).

an inner flesh. Transverse sections show that the sclerotesta has three sharp longitudinal keels with corresponding furrowsnbsp;on the inner face, and between each pair of main ribs are 2—3nbsp;less prominent ridges, usually 12 in all (fig. 426). The sarcotestanbsp;consists of thin-walled parenchyma passing externally into a

öiore lacunar tissue with a palisade-like hypoderm: the sclerotesta consists of thick cells which interlace and form an efhcient protective shell. Both the sarcotesta and sclerotesta are continuednbsp;into the apical region as the wall of the long micropyle, thenbsp;sarcotesta being prolonged beyond the sclerotesta at the apex of

• 126. Trigonocurpus PaTkinsoni. A, longitudinal section; Set, Sc, if, sarcotesta, sclerotesta, inner flesh; mi, micropyle; Pc, pollen-chamber; v, vascular bundles; m, megaspore and prothallus; t, tracheal disc; nt, tracheids in thenbsp;nucellus. B, transverse section of the upper region showing the sarcotesta,nbsp;sclerotesta (black) and the micropyle. C, transverse section of T. Parkinsoni.nbsp;1^, transverse section of Trigonocarpus shorensis, (A, C, after Scott; B, afternbsp;Wild; D, after Salisbury.)

the integument^. The micropyle is triangular in section and may exceed in length the whole seed (figs. 425; 426, A). Its formnbsp;as seen in transverse section (fig. 426, B) suggests the presencenbsp;of wings: this appearance may be deceptive and due to pressurenbsp;or, more probably, it represents an original feature. The seed-body, that is the portion enclosed by the integument, consistsnbsp;of the nucellus, represented by a few crushed layers of cells,nbsp;bounded by a well-defined epidermis; the nucellus is separatednbsp;from the integument from the base of the seed upwards, annbsp;important feature in which this and some other Palaeozoic seedsnbsp;differ from Lagenostoma and the seeds of recent Cycads whichnbsp;are characterised by an integument adnate to the nucellus upnbsp;to the level of the shoulder; the seeds of the Conifer Phyllocladusnbsp;afford an example of separation of integument and nucellus asnbsp;in Trigonocarpus. The innermost layer of the nucellus consistsnbsp;mainly of tracheal tissue investing the large megaspore (fig. 426,nbsp;A, C, m) which is preserved as a contracted membrane detachednbsp;from the nucellus after the death of the seed. At the summitnbsp;of the nucellus is a relatively small pollen-chamber (fig. 426, A, Pc)nbsp;like a broad and low cupola bearing a terminal beak which extendednbsp;some distance into the micropylar tube. No microspores havenbsp;been found in this species, but Oliver^ records the occurrence ofnbsp;multicellular microspores in Trigonocarpus pusillus. The pedicelnbsp;of the seed had a central strand of sclerous tissue penetrated bynbsp;a concentric vascular bundle which gives off six strands to supplynbsp;the sarcotesta (fig. 426, C, v) and then passes into the nucellusnbsp;where it forms a tracheal sheath (fig. 426, A, nt) surrounding thenbsp;lower part of the megaspore and at a higher level breaks up intonbsp;anastomosing strands of tracheids which reach up to the plane ofnbsp;insertion of the pollen-chamber.

A second species described by Scott and Maslen as Trigonocarpus Oliveri has been further investigated by Salisbury who finds that it is an 8-angled seed which cannot be retained in the genusnbsp;Trigonocarpus-. its systematic position ‘must for the presentnbsp;remain uncertain®.’ Dr Arber has recently described a new' speciesnbsp;of Trigonocarpus, T. Moyseyi^, from the Nottingham Coal-field

2 Oliver (04) p. 97.

65. nbsp;nbsp;nbsp;* Arber, E. A. N. (14) p. 95, PI. vi. fig. 1.

123

TKIGONOCARPTTS

(Middle Coal Measures), similar to T. Parkinsoni but much broader in proportion to its length; this species is founded onnbsp;impression without structure.

The species Trigonocarpus Dawesi Lind, and Hutt.^, from the Middle Coal Measures of Lancashire, was founded on castsnbsp;lt;hSering in their large dimensions from those of T. ParUnsom:^nbsp;specimens referred to this species were described by Fiedler^nbsp;from Saxony in 1857 and Lesquereux® figures similar casts fromnbsp;the Upper Carboniferous and Permian rocks of North America.

'^figonocarpus shorensis Salisbury.

This species, founded on specimens from the Lower Coal Measures of Shore, Lancashire*, may exceed 4 cm. in length andnbsp;has a breadth of 2-5 cm. In general plan it agrees with T. ParUn-but there are certain well-marked differences: the micropylenbsp;is much shorter; the thick sarcotesta, attaining a breadth ofnbsp;^ öim. at the base of the micropyle, is characterised by the presencenbsp;of six peripherally placed vascular bundles (fig. 426, D, v) innbsp;contrast to the deeply embedded bundles of T. Parkinsoni.nbsp;Lelow the epidermis of the sarcotesta is a hypoderm formed ofnbsp;indially disposed plates of sclerous tissue similar to that of Myelo-^ylon and different from the palisade-like hypoderm of the type-species. Within the sarcotesta is a hard shell, the sclerotesta,nbsp;characterised by three prominent ribs extending from base tonbsp;^pex and three shorter ribs which reach from the chalaza tonbsp;^hout a third of the length of the seed. The fact that the sarcotesta and sclerotesta pass gradually into one another is a pointnbsp;in favour of the view that the integument is a single structure.nbsp;There appears to be good evidence of the restriction of an innernbsp;flesh to the micropylar region, whereas this tissue in T. Parkinsoninbsp;Was probably continuous over the whole inner face of the sclerotesta. The sarcotesta is lacunar in its outer part as in some othernbsp;types of Palaeozoic seeds, a feature probably connected withnbsp;floating efficiency. Trigonocarpus shorensis occurs in associationnbsp;with Myeloxylon petioles, and there is a resemblance between

' Lindley and Hutton (37) A. PI. 221; Arber loc. cit. p. 95, PI. vi. fig. 8.

I Fiedler (57) PI. xxvii. fig. 39.

Lesquereux (80) A. Pi. 85; (84) A. PI. in.

the seed and the vegetative organs in the structure of the hypoderm as also in the structure of the secretory sacs which are particularlynbsp;numerous in this species. Salisbury draws attention to the closenbsp;resemblance between the form of T. shorensis and the seeds foundnbsp;in organic connexion with pinnae of Neuropteris ohliqua^.

The species T. corrugatus described by Renault^ bears a close resemblance to T. shorensis.

Other Genera founded in part on Reproductive Organs

WHICH MAY BELONG TO THE MeDULLOSEAE.

Codonotheca, Schiitzia, Whittleseya, Dolerophyllum, Otto-

karia, Strobilites.

CODONOTHECA. Sellards.

Codonotheca caduca Sellards. This genus was founded on some spore-bearing bodies from the Coal Measures of Illinois®:nbsp;nothing is known as to the plant which bore them, but Sellardsnbsp;is inclined to associate them with Neuropteris decipiens Lesq.^,nbsp;a species abundant in the same coal-field. Whatever may havenbsp;been the parent-plant it is probable, as the author of the genusnbsp;believes, that Codonotheca is the microspore-bearing organ of anbsp;Pteridosperm. As shown in fig. 427, 5, the form is that of a stalkednbsp;cup consisting in the basal portion of a stout axis, the peripheralnbsp;tissue of which is believed to have been fleshy, containing annbsp;axial rod of conducting tissue running up to the floor of the cup,nbsp;c, and then dividing into six vascular strands, each of which forksnbsp;into two branches. The upper part is composed of six linearnbsp;segments united basally to form the sloping surface of the cup.nbsp;On the inner face of each segment is a more or less well-definednbsp;depression covered with large elliptical spores -29—31 mm. longnbsp;by -18—19 mm. broad (fig. 427, 6, 8). The presence of a mediannbsp;ridge (fig. 427, 8) indicates a bilateral origin. ‘ There is no groupingnbsp;of the spores or other indication of the location of the sporangia,nbsp;which were doubtless more or less completely immersed in thenbsp;tissue, the dividing wall disappearing at maturity.’ The spores

1 nbsp;nbsp;nbsp;See page 115.

2 nbsp;nbsp;nbsp;Renault (96) A. p. 399; (93) A. PI. Lxxxv. fig. 9; Salisbury (14) p. 66.

= Sellards (03) p. 90; (07).

* Lesquereux (80) A. p. 93; (84) A. p. 733, PI. xoiv. figs. 1, 2.

^re seen in fig. 427, 2, 3, on the inner face of the lobes. Some of the specimens have a fairly long pedicel: in the example shownnbsp;in fig. 427^ the fleshy part of the basal portion is not preserved,nbsp;only the more resistant vascular core. In a later account of thesenbsp;Organs Sellards speaks of several lying by the side of a centralnbsp;stalk to which he thinks they were originally attached by slendernbsp;pedicels. In view of Dr Benson’s interpretation of the morphology of Telangium it is permissible to suggest that if a central

II 111 IV V VI

ur.,

jv^

Do. 427. Codonotheca caduca. 1. The vascular tissue preserved as a conical base which was originally surrounded by fleshy tissue icf. 5); I III, VI,nbsp;vascular bundles (x 2).nbsp;nbsp;nbsp;nbsp;2, 3. Segments with spores; c, floor of cup (nat.

size). 4. Vascular tissue as a cone in the middle of the fleshy base (nat. size). 5, Plan of the whole organ opened out flat (nat. size). 6. Sporesnbsp;(x 28). 8. A single spore showing median slit (x 84). (After Sellards.)

sporangium in such a synangium as that of Codonotheca developed ^ megaspore and the peripheral sporogenous lobes were sterilised,nbsp;the result would be an arrangement not unlike the apical regionnbsp;of the seed Physostoma, the tentacles of which have been homo-logised with the canopy of Lagenostoma. There are obvious difficulties in the way of this, perhaps strained, comparison: thenbsp;larger size of the spore-bearing linear segments of Codonotheca

126 MEDULLOSEAEnbsp;[CH.

led Sellards to regard each as a synangium rather than a single sporangium. But precise information as to the structure of thenbsp;American fossils is not as yet available. If the association ofnbsp;Codonotheca with Neuropteris fronds has any significance it wouldnbsp;favour a reference of these organs to the Medulloseae. In thenbsp;absence of anatomical data it is impossible in some cases to distinguish microspore-bearing organs of the Codonotheca type fromnbsp;small seeds enclosed in a lobed cupule or even seeds with a lobednbsp;integument: a case in point is the New Brunswick speciesnbsp;Pterispermostrohus bifurcatus Stopes^.

A Spitzbergen, Culm, fossil recently described by Nathorst^ as Codonotheca (?) pusilla is briefly referred to under the genusnbsp;Pterispermostrohus.

SCHÜTZIA. Geinitz.

This generic name was instituted by Geinitz® for some Permian fossils obtained by Bergmeister Schütz and regarded by the authornbsp;of the genus as probably fertile branches of some Conifer. A morenbsp;complete account was published by Goeppert^ in his ‘Permiannbsp;Flora/ where the name Anthodiopsis Beinertiana occurs onnbsp;the Plates, printed before the publication of Geinitz’s description, but in the text the specimens are referred to Schiitzianbsp;anomala.

Schützia anomala Geinitz.

The type-species, recorded from Bohemia and Silesia, is represented by fertile shoots consisting of a thick main axis bearing apparently two-ranked though probably spirally disposed shortnbsp;lateral branches, each of which terminates in a receptacle withnbsp;numerous crowded linear-lanceolate bracts superficially resemblingnbsp;a partially expanded inflorescence of a Composite. Goeppertnbsp;believed that the branches bore seeds and he refers to this speciesnbsp;a number of detached, longitudinally striated and bluntly terminated, seeds. The same author describes other specimens from

^ Stopes (14) p. 74. See page 66.

2 nbsp;nbsp;nbsp;Nathorst (14) p. 23. See page 67.

3 nbsp;nbsp;nbsp;Geinitz (63) p. 525, PI. vi.

* Goeppert (65) p. 161, Pis. xxiii—iv. The specimens figured by Goeppert, which I saw some years ago in the Breslau Museum, do not show the finernbsp;characters very clearly.

tKe same localities associated with Schütz%a anomala, which he names Dictyothalamus SchrolUanus^: in habit these agree closelynbsp;with Schützia but the receptacles, the reticulate appearance ofnbsp;which suggested the generic name Dictyothalcimus, bear a largenbsp;number of small bodies regarded as seeds. The preservation ofnbsp;the fossils is not such as to enable us to determine their truenbsp;nature but it is probable that Schützia and Dictyothalamus arenbsp;not generically distinct. In his description of Dictyothalamusnbsp;^oeppert suggests that the two associated types may be thenbsp;niale and female shoots of one plant, but he speaks of seeds innbsp;both cases. Schimper^, who unites Dictyothalamus with Schützia,nbsp;regards the latter as female and the former as male.

Schützia Bennieana Kidston.

This species, described by Kidston® from the Calciferous series of Scotland, differs from S. anomala in its much more slendernbsp;axis and in the relatively narrower and less globular clusters ofnbsp;bract-like appendages. The principal axis bears three lateralnbsp;branches with terminal clusters of acute and narrow linear scale-leaves. No seeds were found in association with the spegimens.

Schützia permiensis (Renault).

Renault founded this Permian species as Antholithus permiensis^ on a specimen from Lodèveit consists of an incompletenbsp;inflorescence 64 cm. long bearing four lateral branches with stalksnbsp;1’5 to 2 cm. long terminated by clusters of small oval bracts 5 mm.nbsp;fong. Renault compares the fossil with the recent Conifersnbsp;^hptostrobus and Tsuga, but it exhibits a much closer resemblancenbsp;fo Schützia anomala.

The genus Schützia, originally described from Permian strata, 1® recorded also from Westphalian strata in North Africa® as wellnbsp;ns from Lower Carboniferous rocks in Scotland. The data atnbsp;present available are insufhcient to determine the morphologicalnbsp;nature of the fertile branches: the evidence adduced by Goeppertnbsp;rn support of the occurrence of seeds is not convincing and the

interpretation of the bract-like appendages is still an open question; they may have formed a cupular investment to seeds, but in thenbsp;Scotch species the general appearance rather suggests that theynbsp;may be microspore-bearing organs comparable with those ofnbsp;Codonotheca^. There are no adequate grounds for supposingnbsp;SchUtzia to belong to the Coniferales, a view advanced by somenbsp;authors; it is much more likely to represent the fertile shootsnbsp;of a Pteridosperm.

WHITTLESEYA. Newberry.

The genus Whittlesey a, referred by many authors to the Ginhgoales, has no substantial claim to be regarded as allied tonbsp;that group: its position is still uncertain, but the recent discoverynbsp;of fertile specimens suggests the probability of a relationship tonbsp;Potoniea and an identification of Whittleseya as another form ofnbsp;microsporophyll of a Pteridosperm.

size.)

The generic name was given by Newberry^ to some leaves, or possibly leaflets, originally described by C. Whittlesey from

1 See page 124. nbsp;nbsp;nbsp;^ Newberry (54).

the Coal Measures of Ohio. 'Whittleseya is represented by species from several North American localities^ in Ohio, Pennsylvania,nbsp;Arkansas, Nova Scotia, and New Brunswick^; it occurs in Silesianbsp;®'öd has recently been found in the English Coal Measures®.nbsp;The genus is confined to Upper Carboniferous strata.

The leaves are fairly thick; the lamina is oblong, cuneate, broadly triangular or linear, usually rounded and truncate (fig. 428,nbsp;C), generally dentate at the distal end, the proximal portionnbsp;being gradually or abruptly contracted and occasionally prolongednbsp;into a short pedicel. The veins or ribs are parallel to the sidesnbsp;the lamina and except near the base unbranched.

Whittleseya elegans Newberry.

The type-species, from North America and Europe, is characterised by its shovel-like lamina from 3 to 6 cm. long closely resembling in shape some lepidopterous scales; the surface isnbsp;ribbed, each rib corresponding to a tooth on the distal margin;;nbsp;en each of the parallel ridges are 4—5 longitudinal lines indicatingnbsp;either veins or stereome strands (fig. 428, A, C). The examinationnbsp;ef preparations made by Dr Kidston from a leaflet of this speciesnbsp;enables me to add a few facts with regard to the microspores.nbsp;The spores, which cover almost the whole surface of the lamina,nbsp;®how a tendency to a more or less definite arrangement in longi-fndinal rows. Two types of cuticularised membrane are represented among the associated fragments: in some pieces of cuticlenbsp;fhe cells are short and have straight walls while in others thenbsp;preservation is inferior and the cells appear to be longer andnbsp;narrower. One or both of these membranes probably belong tonbsp;® sporangia. The oval slit, which is a striking feature onnbsp;^ci^eral of the spores (fig. 429), points to their bilateral naturenbsp;^¦nd dehiscence along the major axis. A comparison of thesenbsp;“^ores with those obtained by Kidston from the English speciesnbsp;i^ttleseya fertilis reveals a very close agreement both in sizenbsp;^nd shape and confirms the identification of the Staffordshirenbsp;pecimens as leaflets of Whittleseya. The large size of the micro-Pores and the gaping oval aperture in some of them are features

quereux (80) A. p. 523, Pi. iv; (84). For other references see Potonie (04).

^ Thomas, H. H. (12); Kidston (14) p. 166.

9

in which they agree closely with the spores of Dolerophyllum fertile described by Kenault^. In both cases the spores tend tonbsp;be arranged in long groups and they are practically identicalnbsp;in form and in the nature of the exine; those of Dolerophyllumnbsp;are 280jli long while those of W. fertilis reach a length of 220ja.nbsp;In some of the Whittleseya spores the exine has split as in thenbsp;specimen shown in fig. 429, but in others there are two curvednbsp;lines along which dehiscence has begun, a character in whichnbsp;the spores appear to be identical with those of Dolerophyllum

m9.

Big. 429. Microspores of Whittleseya eleyans. A, a group of spores; B, a single spore. (Preparations made from an American specimen, No. 2314, innbsp;Dr Kidston’s Collection.)

described by Renault who speaks of dehiscence by means of an operculum. There is, I venture to think, little doubt as to thenbsp;very close affinity of the two types. The systematic positionnbsp;of Dolerophyllum is not certainly established; if the genericnbsp;identity of the leaves described as D. Berthieri Ren. and thenbsp;petrified specimens named D. fertile is assumed, it is a legitimatenbsp;inference that the genus is founded on fertile pinnules of a Pterido-sperm with foliage of the Neuropteris or Cyclopteris form. Itnbsp;would seem probable that both Whittleseya and Dolerophyllum

1 Renault (93) A. PI. Lxxii; (96) A. p. 268. See page 137.

fertile are microspore-bearing leaflets of Pteridosperms, possibly of some Medullosan plants. The leaflets of Whittleseya agree innbsp;form fairly closely with those of Potoniea adiantiformis Zeill.nbsp;described on a previous page^ as the male organs of a Pteridosperm.nbsp;The specimens described by Lesquereux from Pennsylvanianbsp;W. integrifolia and W. undulata are less satisfactory thannbsp;elegans. The Arkansas species W. microphylla^, characterisednbsp;fcy the obcuneate form of the lamina, is said to occur not onlynbsp;detached leaflets but in loose bunches at the ends of slendernbsp;^xes, a circumstance favourable to the suggestion, based on thenbsp;recently described English specimens, that the Whittleseya leavesnbsp;rira-y be fertile pinnules of a Pteridosperm frond. Among othernbsp;species attributed to Newberry’s genus is W. hrevifolia Wh. fromnbsp;^ova Scotia^ with much smaller broadly triangular leaves 7 mm.nbsp;long exclusive of the petiole and 8 mm. broad at the distal endnbsp;(%• 428, B). Dr Matthew* has also described a Canadian speciesnbsp;concinna from New Brunswick in beds assigned by Dr Stopes®nbsp;fo the Westphalian series.

Whittleseya Jertilis Kidston.

Since the discovery of Whittleseya elegans in the Coal Measures ®f Staffordshire recorded by Mr Thomas, Dr Kidston has publishednbsp;account of some specimens from the same district under thenbsp;name Whittleseya (1) fertilis^: these consist of smaller cuneatenbsp;scale-leaves or leaflets 1-4—2-4 cm. long and 8—9 mm. broad;nbsp;f'fio lamina has a dentate upper margin and is longitudinallynbsp;i^ibbed. The scales occur in superposed pairs, closely fitting butnbsp;not organically connected, at least in the state in which they arenbsp;preserved; each pair forms a sporangium-like case enclosingnbsp;numerous spores but the actual sporangia or synangia have notnbsp;een preserved. Kidston describes the spores as 210—222/x innbsp;gth, elliptical, and characterised in many cases by an oval

* gt; they are practicallv identical with the microspores of W. elegans.

^ Page 111. nbsp;nbsp;nbsp;2 White (01) p. 108.

“ Ibid. p. 104, PI. VII. figs. 3, 3«. nbsp;nbsp;nbsp;* Matthew (10).

Stopes (14) p. 78. nbsp;nbsp;nbsp;« Kidston (14) p. 166, PI. xv. figs. 1—10.

9—2

DOLEROPHYLLUM. Saporta.

This name was proposed^ primarily for a large ovoid petrified bud composed of rolled Cyclopteroid leaves from Permian rocksnbsp;in the Ural Mountains, which had been previously described bynbsp;more than one writer under different names and regarded as anbsp;young shoot of a Palm or other Monocotyledon. Eichwald^,nbsp;who published good drawings, called the fossil Noeggerathianbsp;Goe-pperti. Saporta connected with this species some leaf-impressions from the Permian of Bohemia described by Goeppert® asnbsp;Noeggerathia cyclopteroides: in his family Dolerophylleae'* thenbsp;French author included other leaves which are probably notnbsp;closely related to the type-species, Dolerophyllum Goepperti.nbsp;The Dolerophylleae are spoken of by Saporta and Marion® asnbsp;Progymnosperms. Before the publication of Saporta’s notenbsp;Grand’Eury had instituted the genus Doleropteris^ and the familynbsp;Doleropteroideae; in the former he included several forms ofnbsp;leaves agreeing generally with Goeppert’s Noeggerathia cyclopteroides. Zeiller’^ adopts Grand’Eury’s designation for thenbsp;B,ussian fossil in preference to Dolerophyllum, a choice justifiednbsp;by considerations of priority; but the latter name is retainednbsp;in this account as it was assigned by Saporta to the specimen ofnbsp;greatest botanical interest, namely Dolerophyllum Goepperti, andnbsp;because it does not suggest affinity to Eerns.

Dolerophyllum Goepperti (Eichwald).

The type-species is from the Zechstein of Orenburg in the Urals and no specimens having precisely the same structure havenbsp;been found elsewhere. Eichwald assigned it, with leaf-impressionsnbsp;of various kinds, to the Noeggerathieae and named it Noeggerathianbsp;Goepperti: it had previously been described by Kutorga® asnbsp;Araides crassispatha and Unger® included it among the Palms asnbsp;Palaeospathe aroidea. The species has been described also bynbsp;Saporta and Marion and by Renault^®. The following account is

^ Saporta (78). nbsp;nbsp;nbsp;^ Eichwald (55) PI. xviil. fig. 18; (60) p. 252.

® Goeppert (65) p. 157, PI. xxi. fig. 4. nbsp;nbsp;nbsp;^ Saporta (78^).

^ Saporta and Marion (85) pp. 16, 68.

8 Grand’Eury (77) A. p. 192. nbsp;nbsp;nbsp;’ ZeiUer (00=) B. p. 217.

8 Kutorga (42). nbsp;nbsp;nbsp;8 Unger (50) A. p. 334.

Renault (96) A. p. 262.

based on sections cut from a specimen in the British Museum^ which, though assigned on the label (within a query) to France andnbsp;named Dolerophyllum Berthieri, is undoubtedly Eichwald’s speciesnbsp;from East Eussia.

The specimen (fig. 430) is 9 cm. long and 4-2 cm. broad: at the slightly contracted and broken base is a piece of immaturenbsp;axis (fig. 430, B, a) 12 mm. in diameter overtopped by a mass ofnbsp;olosely packed leaves encircling one another like the bulb-scalesnbsp;nf an Onion (fig. 430 A, C)^. Most of the leaves included in the

bud were attached to the axis below the broken base. The lt;iurved, dichotomously branched, veins are seen on some of thenbsp;pieces of lamina on the surface of the bud (fig. 430, A). Thenbsp;considerable breadth of the leaves is demonstrated by the longitudinal and transverse sections. In fig. C most of the laminaenbsp;can be traced through the whole height of each of the steep-sidednbsp;ui'ches: a few overlapping margins are seen in fig. D. The veinsnbsp;for the most part imperfectly preserved and appear as clearnbsp;^ No. V. 8114.

^ A specimen from Orenburg in the Dresden Museum shows the same surface-Watures as the British Museum specimen and agrees with the originals of Goeppert’s gures which are in the Breslau University Museum.

spaces at regular intervals in the brown niesophyll. The axis of the shoot consists of homogeneous parenchyma except nearnbsp;the sloping sides where narrow dark bands (fig. 430, B, a) marknbsp;the position of desmogen-strands of thin-walled elongated elements

m.

.if

Cl

Fig. 431. Dolerophyllum Goepperti. Transverse sections of leaves, e, epidermis; s, secretory ceils; t, transfusion-tracheids; px^ protoxylem. (British. Museum.)

representing an early stage in the development of vascular bundles some of which have already produced spiral tracheids. Shortnbsp;secretory cells accompany the immature conducting elements.nbsp;The lamina slightly exceeds 2 mm. in thickness in the broadestnbsp;part; the mesophyll is composed of large parenchymatous cells

of elliptical or spherical form often loosely attached owing to the ''^ell-developed system of intercellular spaces. The lower epidermis, assuming that the outer face of the rolled leaves is thenbsp;morphologically lower surface, forms a uniform layer of palisadenbsp;Cells characterised by their free conical ends (fig. 431, A, B, e)nbsp;quot;quot;hich in some oblique sections appear as sharply pointed papillaenbsp;quot;^ith almost filiform apices; but while the cells were doubtlessnbsp;papillose like those of the epidermis of a velvety petal, the pointednbsp;form is due in part to the greater distinctness of the dark contentsnbsp;as compared with the lighter cell-walls. The upper epidermisnbsp;is much less distinct; it consists of smaller flattened cells withnbsp;Occasional stomata. Renault' figures a specimen with stomatanbsp;iquot; a better state of preservation. The vascular bundles arenbsp;rendered conspicuous by large secretory cells on the lower side,nbsp;in the larger veins in the form of an arc or irregular group (fig.nbsp;d32. A), but in the finer veins as single cells (fig. 431, A, B). Thesenbsp;Sacs resemble the tannin cells accompanying the veins in a leafnbsp;of Ginkgo {cf. fig. 631, Gl). The xylem-elements are of two kinds,nbsp;(i) elongated spiral and scalariform conducting elements, formingnbsp;® vertical plate of a few rows in the larger veins (figs. 431, 432)nbsp;or a small compact group in the more slender veins (fig. 413, A, B);nbsp;(if) much larger isodiametric cells with reticulate or spiralnbsp;thickening resembling the transfusion-tracheids of Conifers or,nbsp;perhaps more closely, similar elements in the leaves of Lepido-dendron. These short tracheids are especially abundant on thenbsp;flanks of the conducting tracheids (figs. 431, t; 432, A, t), butnbsp;ffley sometimes form a complete investment. In the obliquelynbsp;cut vein reproduced in fig. 431, D, the transfusion-tracheids arenbsp;abundant: a few are enlarged in fig. 431, E. In the smaller veinsnbsp;(flg- 431, A, B) they are represented by the larger elements, t,nbsp;cu the sides of the conducting strands. The protoxylem liesnbsp;close to the upper edge in the middle line (px, figs. 431, A; 432, A);nbsp;'f IS difficult to determine its precise position, but it would seemnbsp;fc be shghtly internal, the bundle being not quite endarch. Nonbsp;phloem was recognised in the British Museum specimen, but itnbsp;presumably occurred, if present, where the black patch is shown

Renault (96) A. p. 265, fig. 43.

in fig. 432, A. Renault describes some phloem in sections which he examined.

The mesophyll next the upper surface is in most cases represented by spaces between the veins which give a crenulated outline to the parenchyma (fig. 430, C, D); in some places thenbsp;spaces contain remains of very loose and crowded cells suggestingnbsp;the original presence of very lacunar tissue or possibly of thin-walled storage-cells. The confinement of stomata to what isnbsp;assumed to be the upper surface may, as Renault and othersnbsp;have suggested, indicate leaves which floated on water, annbsp;inference opposed to the view that the gaps in the mesophyllnbsp;mark the position of water-tissue.

No specimens have been described which enable us to correlate with certainty mature leaves or foliage-shoots with the petrifiednbsp;bud. It is, however, not improbable that the impression fromnbsp;Mount Pelé near Epinac named by Renault Dolerophyllumnbsp;Berthieri^ may be correctly referred to the same genus. Thenbsp;type-specimen consists of an axis, whether a rachis of a compoundnbsp;leaf or a shoot with simple leaves cannot be determined, bearingnbsp;partially overlapping more or less orbicular leaves 18—20 cm. innbsp;diameter, with a Cydopteris venation. Among other leaves ofnbsp;unknown affinity referred to the same genus attention is drawnnbsp;to Dolerophyllum pseudopeltatum (Grand’Eury)^ with an orbicularnbsp;lamina reaching in some specimens 22 x 19 cm. Specimensnbsp;of Dolerophyllum pseudopeltatum are figured by Renault from thenbsp;Commentry coal-field®, some of which reach a diameter of 12 cm.nbsp;The only British specimen of a leaflet of this type which I havenbsp;seen is one in Dr Kidston’s collection from the Stephanian series,nbsp;Glamorganshire. It is probable that some at least of thenbsp;impressions assigned to Dolerophyllum or Doleropteris would benbsp;more appropriately included in Cydopteris or Cardiopteris andnbsp;may have been borne on the axis of large Pteridosperm fronds.nbsp;Grand’Eury^ has also called attention to the difficulty of distinguishing the larger Cydopteris leaflets from Dolerophyllum. Some

1 nbsp;nbsp;nbsp;Renault (96) A. p. 262, PI. xxii. fig. 1.

2 nbsp;nbsp;nbsp;Grand’Eury (77) A. p. 196, PI. xvi; (90) A. PI. viii. fig. 1; Zeiller (06) B. p. 192.nbsp;® Renault and Zeiller (90) A. p. 556, PI. LVii.

« Grand’Eury (04).

of the Cyclopteroid leaflets figured by RoehP on Neuropteris fronds differ but slightly from those of D. pseudopeltatum. The shootnbsp;showing large leaf-scars figured by Saporta and Marion^ as proba-fgt;ly the axis of'a Dolerophyllum may well be a piece of Cordaites.

^licrosporophylls assigned to Dolerophyllum.

Certain problematical fossils found in association with the sterile leaves of Dolerophyllum Berthieri have been described by

Dolerophyllum

Dolerophyllum

euault as the male organs of that species. These are elliptical os, 6x5 cm., with an excentrically placed stalk: embeddednbsp;^ carbonised lamina are numerous rows of elliptical bodies,nbsp;quot; Roehl (69) B. PI. XVII.

410/x X 280/x, characterised by two curved longitudinal grooves on the surface and regarded by Eenault as pollen-grains. Thenbsp;chains of these microspores radiate outwards from the neighbourhood of the stalk and cover most of the surface of the disc (fig.nbsp;432, B). Some silicified pieces of similar spore-bearing discsnbsp;from Grand’ Croix named Dolerophyllum fertile'^- afford additionalnbsp;information as to these remarkable reproductive organs. Thenbsp;earlier account of this species by Renault is confirmed by Solms-Laubach^ who examined the original sections. The peltatenbsp;fleshy discs preserved as incomplete specimens consist of lacunarnbsp;parenchyma 15—18 mm. thick traversed at right angles to thenbsp;surface by numerous loculi (fig. 432, C), circular or oval in transverse section, containing large numbers of microspores, s, similarnbsp;in size and form to those on the carbonised discs of the Mt Pelénbsp;specimen. Vascular strands occur between and parallel to thenbsp;spore-chambers. The spores contain 8—10 cells (fig. 432, D)nbsp;and Renault believes that dehiscence of the exine occurred alongnbsp;the two deep grooves which mark the limits of an operculum.nbsp;He emphasises the peculiar structure of the microspores bynbsp;speaking of them as prepollinia: in size and in the presence ofnbsp;internal cells (? male prothallus) they resemble the spores foundnbsp;in the pollen-chamber of a seed described by Renault as Aetheo-testa elliptical which he thinks may belong to a member of thenbsp;Dolerophylleae. It has also been suggested that Codonospermumnbsp;may be a seed of Dolerophyllum*. An unconvincing specimennbsp;described by Saporta and Marion® as a seed-bearing bract isnbsp;regarded by them as referable to Dolerophyllum, but the evidencenbsp;for any connexion is far from satisfactory.

There is nothing definite to be said with regard to the affinity of Dolerophyllum Goepperti or the microsporophylls representednbsp;by D. fertile and the specimens associated with D. Berthieri.nbsp;Renault considers that both sterile and fertile specimens belongnbsp;to the same genus, which he assigns to a position between Pterido-phytes and Cycads. As Solms-Laubach says, the evidence supplied by the structure of the veins of D. Goepperti in favour of a

1 Renault (96) A, p. 267, PI. lxxii.

^ See Chapter xxxv

^ Saporta and Marion (85) fig. 37, p. 76.

cycadean alliance is not convincing. The type of vernation is unlike that of any known Cycad or indeed of any Gymnosperm;nbsp;the large size of the leaves is another though weaker objectionnbsp;to this comparison, as the pinnae of Bowenia (fig. 391) and especiallynbsp;those of some species of Zamia (fig. 388), are of equal or largernbsp;dimensions. If, as seems probable, the xylem-strands are mesarchnbsp;that is a point of contact with recent Cycads, but the bundle asnbsp;a whole bears but a remote resemblance to that of a cycadeannbsp;leaf and is much more like the veins of Ginkgo. The bud shownnbsp;iu fig. 430, A, is probably a young shoot and not merely a largenbsp;compound leaf. If it were an unexpanded frond of Neuropterisnbsp;bearing Cyclopteris pinnules we should expect to find indicationsnbsp;of scattered desmogen-strands such as would occur in the Myelo-^ylon type of rachis. The resemblance to most forms of Cordaitesnbsp;IS by no means close though a few leaves referred to that genusnbsp;(c-5'. C. circularis, fig. 468, B) are similar to those of Dolerophyllum^.

The male organs are unlike those of any other plant: they Olay be described as sporophylls with microsporangia or perhapsnbsp;®ynangia embedded in the mesophyll and containing microgporesnbsp;siuiilar to those of some Pteridosperms or true Gymnosperms.nbsp;Attention has been called to the close resemblance of the sporesnbsp;shown in fig. 432, C, D to those recently discovered by Kidstonnbsp;^ud referred to the genus Whittleseya (fig. 429), and it is very probable that the striking similarity is an index of affinity.

Ottokaria. Zeiller.

Ottokaria bengalensis Zeiller. A specimen of doubtful affinity from the Lower Gondwana (Karharbari beds) of Passerabhia,nbsp;fodia, was originally described b}^ Zeiller^ as Feistmantelianbsp;^^ngalensis, but in a postscript he substitnted the name Ottokarianbsp;cri the ground that Feistmantelia had previously been employednbsp;by Lester Ward. Fig. 433 is drawn from the original specimen:nbsp;A consists of a stalk attached in a slightly excentric position tonbsp;^11 almost orbicular lamina, 2-5 cm. in diameter, with subacutenbsp;’narginal teeth and traversed by numerous radially disposed

^ ^ Schmalhausen (87) PI. v. figs. 7—9: this specimen, figured as Dolerophyllum °^Pperti, is very similar to Cordaites circularis [Grand’Eury (90) A. PI. vi. fig. 15].

quot; Zeiller (02) B. p. 34, PI. iv. figs. 9, 10.

striations. Zeiller compares the fossil with Whittleseya elegans and Rhipidopsis ginkgoides and assigns it with some hesitationnbsp;to the Salisburieae. An examination of the type-specimen lednbsp;me to form the opinion that it may be a cupular organ of a Pterido-sperm that enclosed a seed. The lamina is slightly concave andnbsp;has the form of a shallow cup; moreover the surface-featuresnbsp;resemble those of a bract rather than the regularly veined lamina