The Role of Auxin in the Correlative
Inhibition of the Development of
Lateral Buds and Shoots

PROEFSCHRIFT TER VERKRIJGING VAN
DE GRAAD VAN DOCTOR IN DE WIS-
EN NATUURKUNDE AAN DE RIJKS-
UNIVERSITEIT TE UTRECHT, OP
GEZAG VAN DE RECTOR MAGNIFICUS
DR. J. BOEKE, HOOGLERAAR IN DE
FACULTEIT DER GENEESKUNDE,
VOLGENS BESLUIT VAN DE SENAAT
DER UNIVERSITEIT TE VERDEDIGEN
TEGEN DE BEDENKINGEN VAN DE
FACULTEIT DER WIS- EN NATUURKUNDE
OP MAANDAG 9 MEI 1938 TE 15 UUR

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T'S :

Gaarne wil ik de gelegenheid aangrijpen, die het verschijnen
van dit proefschrift als afsluiting van mijn universitaire oplei-
ding mij biedt, om allen dank te zeggen, die tot mijn academi-
sche vorming hebben bijgedragen.

Met genoegen denk ik terug aan de colleges en practica, die
ik in mijn eerste studiejaren heb mogen volgen van wijlen
Professor Niersteasz, van U, Hooggeleerde van Romburgh, Kkuyt,
Rutten en Moll, en van U, Zeergeleerde Strengers, Kirsch, van
OoRDT, ScHUURMANS STEKHOVEN en VoNK. Indien ik niet gedwongen
ware geweest mij te beperken, had ik gaarne aan verschillende
der door U gedoceerde vakken wat langer mijn belangstelling
gegeven.

In de daaropvolgende jaren is het vooral wijlen Professor Went
geweest, die aan mijn studie leiding en richting gegeven heeft.
Ik beschouw het nog steeds als een groot voorrecht, dat ik in het
laatste jaar van zijn verblijf in Utrecht als praeses van de
Utrechtse Biologen Vereniging op nauwe wijze met hem in con-
tact ben geweest; zijn nauwgezette plichtsbetrachting, grote werk-
kracht en helder inzicht zullen mij bij mijn latere werk steeds
tot voorbeeld en stimulans zijn.

Hooggeleerde Koningsberger, Hooggeachte Promotor, de tijd,
waarin ik onder Uw leiding dit proefschrift heb mogen bewerken,
is voor mij een zeer aangename geweest. Voor Uw steun en kri-
tiek, voor Uw persoonlijke belangstelling en de aangename sfeer,
die gij op Uw laboratorium wist te doen heersen, wil ik U hartelijk
dank zeggen.

Hooggeleerde Pulle, veel aantrekkingskracht heeft de bizon-
dere plantkunde niet op mij uitgeoefend, toch ben ik U dankbaar,
dat gij mij enig inzicht hebt gegeven in de moeilijke problemen,
die hij heeft op te lossen.

Hooggeleerde Jordan, grote bewondering heb ik voor het inzicht
in wetenschappelijke problemen, waarvan Uw colleges blijk geven;
bizonder erkentelijk ben ik U voor het feit, dat gij mij in vraag-
stukken van algemeen biologische aard hebt weten in te leiden.

Hooggeleerde Westerdijk, Uw heldere colleges en het werken
op Uw laboratoritmi in Baarn gaven mij, naar ik meen, een goede
grondslag voor mogelijke latere werkzaamheden op phytopatholo-
gisch gebied. Daarnaast waren voor mij van grote waarde Uw
frisse kijk op mensen en toestanden, en de raad en aansporingen,
die gij mij en anderen bij vele gelegenheden wist te geven.

Hooggeleerde Honing, Uw college in de erfelijkheidsleer was
voor mij, vooral in de laatste jaren van mijn studie, een van de

aangenaamste uren van de week. Was het Uw persoon, of het
vak dat mij zo boeide? Vermoedehjk wel beide, en m het
bizonder ook wel de grote liefde en de gedegen wetenschappelijke
wijze waarmee gij het doceerde. Aan het werken op Uw labora-
torium in Wageningen heb ik niets dan aangename herinneringen
en vooral ook waardeer ik het, dat ik daardoor in contact kwam
met het prachtige wetenschappelijke werk, dat op velerlei gebied
in Wageningen verricht wordt.

Hooggeleerde de Bussy, op zeer onderhoudende wijze hebt gij
mij doen kennis nemen van de economische en biologische vraag-
stukken, die zich bij de tropische cultures in ons Indie voordoen,
en meer nog dan tevoren heeft dit bij mij het verlangen opge-
wekt daar als bioloog een werkkring te vinden.

Waarde Varossieau, ik ben U dankbaar, dat gij mij hebt ge-
wezen op de paedagogisch-didactische vragen, waarmee een
leraar in de biologie te maken krijgt. Bij Uw enthousiaste pogm-
gen tot het verkrijgen van een betere leraarsopleiding in univer-
sitair verband heb ik met veel genoegen met U samengewerkt.

Waarde van Eekeren, Uw lessen in de biologie aan het Christe-
lijk Lyceum te Zeist zijn voor mij een voortreffelijke voorberei-
ding geweest op mijn latere studie aan de Universiteit, gaarne
breng ik U daarvoor nog dank.

Terugziende op mijn studententijd ben ik bovenal ook erkente-
lijk voor het feit, dat ik lid heb kunnen zijn van het Utrechts
Studenten Corps en van de Vrijzinnig Christelijke Studenten
Bond Zij beiden toch, hebben belangrijk bijgedragen tot mijn
academische vorming; dankbaar ben ik voor de vele vriendschap,
die ik in hun midden, èn in de kring der biologen heb mogen
ondervinden.

Tot slot nog een woord van dank aan allen, die mij bij de
bewerking van dit proefschrift van dienst zijn geweest. Van de
assistenten op het Botanisch Laboratorium waren het in het
bizonder gij, van Raalte en Thomas, die steeds met grote bereid-
willigheid voor mij klaar stondt. Buitengewoon aangenaam was
mij de steun, die ik bij het uitvoeren van mijn proeven in de
zomer van het vorige jaar achtereenvolgens van U, Oppenoorth,
en van mijn verloofde mocht ondervinden. De hortulanus Romeyn
en de tuinlieden van Staveren en Brouwer dank ik voor hun
hulp bij het opkweken en verzorgen van mijn proefplanten, de
technicus de Bouter en Willemsen voor hun hulp bij technische
storingen, Lobel voor het schoonmaken van mijn glaswerk en
de tekenaar de Bouter voor de uitstekende uitvoering van mijn
tekeningen en grafieken. Mijn hartelijke dank ook aan hen, die hun
krachten gegeven hebben aan de vertaling van het manuscript.

THE ROLE OF AUXIN IN THE CORRELATIVE INHIBITION
OF THE DEVELOPMENT OF LATERAL
BUDS AND SHOOTS

The auxin content of plants with inhibited lateral shoots 255
§ 1. The auxin content of intact „two-shoot plantsquot; of

It is a long known phenomenon, that if in a plant the terminal
bud of one of its shoots is removed, one or more of the axillary
buds will develop. As long as men were interested in agricul-
ture, horticulture and forestry, this facts must have been known,
since it is the base of all pruning. In order to obtain tightly-
stooled plants squeezing of the terminal bud is also often ap-
plied. In fir trees the phenomenon is particularly striking. When
these for some reason have lost their terminal shoot, one, rarely
more, of the lateral shoots quite close to it, growing in a hori-
zontal direction first, will erect itself and grow in a vertical
direction, thus physiologically replacing more or less the lost
terminal shoot. An analogous phenomenon occurs after removing
of the tip of the main root; one or more of the lateral roots
below the tip change their direction of growing, bend downwards
and physiologically replace the main root. This phenomenon,
though known for a long time, remained unexplained until re-
cently and then was only elucidated to a certain extent.

It was first explained by assuming that specific root- and
shoot-forming substances existed, which were transported in
opposite directions from apex to base and reversely. Another
explanation was that the growing apex absorbed all the nutri-
tive material available, so that the lateral buds became short
of food and could not develop. On the other hand some other
investigators thought, that the terminal shoots had an inhibiting
influence on the lateral buds and shoots, on account of which
it was called a phenomenon of correlative inhibition. Besides
the terminal shoot, the leaves too appeared to exert such an
inhibiting influence on the development of their axillary buds.

The problem was brought nearer to its solution, when it tur-
ned out, that here auxin, the phytohormone of cell elongation,
is the correlation carrier. Tlie auxin which is produced in
large quantities by the terminal bud and by the young leaves

and is transported in basal direction would then inhibit the
development of lateral buds and shoots in the intact plant. Soon,
however, the difficulty arose how to explain this growth in-
hibiting action of auxin, as its action is generally growth-pro-
moting. Several theories tried to solve this problem.

According to one of them the phenomenon would still be due
to a direct action of auxin, but in this sense, that either the
auxin coming from the terminal bud would prevent the lateral
buds from producing auxin themselves and so from developing,
or the high concentration of the auxin would inhibit this deve-
lopment. According to another theory, however, auxin would
act here only indirectly. The auxin first promotes growth in the
main stem and from this initial growth process a secondary
growth-inhibiting influence acts upon the lateral buds and shoots.
According to a third theory, besides auxin, at least two other
specific substances, would be needed for the development of
buds and shoots and these substances would be transported in
acropetal direction. The function of auxin would only consist
in attracting these substances to the production center of the
auxin.

None of these theories gives an exhaustive explanation of the
phenomena, as will be seen from the following discussion of
literature. For this reason it seemed desirable to examine more
closely and as quantitatively as possible the role of auxin in
the correlative inhibition of lateral buds and shoots.

§ 1. Early experiments: formative substances, nutritive ex-
haustion or inhibiting substance.

Sachs (1874) in his essay „Ueber das Wachsthum der Haupt-
und Nebenwurzeln IIquot; points out, that after cutting off the tip
of the terminal root of Vicia Faba, the lateral roots, growing
out from the cut surface, will grow downwards much more
perpendicularly than the lateral roots in an intact plant. He
compares this to the behaviour of a lateral shoot a little beneath
the terminal shoot, which, after the latter has been removed,
will erect itself and grow perpendicularly upwards, in a way
replacing the terminal shoot. Sachs (1880, 1882) tries to explain
this by assuming that specific root-forming substances are flo-
wing from the leaves to the roots in the intact plant, while

reversely shoot-forming substances are moving upwards to the
terminal and lateral shoots.

As a matter of fact this was an organogenetic version of the
theory of Duhamel du Monceau (1758), who assumed two kinds
of sapstreams, one flowing downwards from the leaves and ser-
ving for the formation of the roots, and the other moving up-
wards which promotes the growth of shoots and leaves.

Darwin (1880) repeats the experiments of Sachs, but he does
not find it necessary to cut off the tip of the main root for
making one of the lateral roots replace the main root, as the
same result could be obtained by pinching young radicles a
little above their tips between the arms of a U-shaped piece
of leaden wire. He considers this phenomenon as well as the
analogous one, where the main shoot of plants and trees is
removed, as a question of nutrition: the increased flow of sap
into the lateral roots or shoots is the cause of their rapid deve-
lopment.

Errera (1904), however, concludes from his experiments that
after the removal of the terminal shoot of Picea excelsa, the
sapstream cannot be responsible for these phenomena. In intact
fir trees the lateral shoots will develop quite nicely and do not
make the impression of lacking anything. This makes him as-
sume that the terminal shoot has a specific inhibiting effect on
the lateral shoots, so to say of a catalytic nature.

Goebel (1902, 1903) originally tried to explain this correlation
phenomenon by applying the theory of Sachs of the organ-
forming substances as well as by the theory that the one part
should monopolize the nutritive material to such an extent,
that the other parts could not obtain sufficient to enable growth
to go on. In Goebel's opinion the important cause is the direc-
tion in which the constructive material moves, the vegetative
points acting as centers of attraction for the plastic material,
their influence being weaker or stronger according to their
position. Later (1908) Goebel thought that nothing but the con-
centration of the nutritive material could cause this correlation
phenomenon.

MacCallum (1905) on the other hand, concluded from his
regeneration experiments with leaves of Bryophyllum calycinum,
that the means by which a terminal bud suppresses the develop-
ment of the other meristematic cones of the plant do not lie in
the withdrawal by the former of the nutritive materials or of
the water, nor to a lack of a definite „formative substancequot;.
He believes in some influence independent of all these, which

an organ, acting perhaps along protoplasmic connections, is able
to exert over other parts thus preventing their growth.

Mogk (1913) too, from his extensive experiments about the
correlations of buds and shoots of various plants and trees,
draws the conclusion that nutrition does not play an important
part. The correlatively inhibited shoots rather seem to have
lost the capacity of assimilating the available nutritive material.

According to Loeb (1915) the flow of material in the plant is
responsible for phenomena of growth in leaves and stems of
Bryophyllum. The apparent inhibition of growth in one place
would be simply due to the fact that, under the conditions of
the experiment, the substances required for growth flow to
some other place and are retained there. Further the removal
of inhibition creates conditions, which will force the substances
to flow where we want growth to occur. In a later publication
(1917) Loeb, however, tries to account for the correlative in-
hibition by assuming a geotropic hormone and shoot- and root-
forming hormones. This would explain the fact that in certain
fir trees a horizontal branch next to the apex may suddenly
become negatively geotropic, when the apex is cut off. After the
decapitation the hypothetical geotropic substance, which before
was flowing to the apex, now can flow into the horizontal
branches next to the apex and the one which by chance gets a
little more of the substance than the others, will become ver-
tical. From the fact that in Bryophyllum the apical bud prevents
the lower ones from growing out Loeb (1917a) concludes, how-
ever, that there an inhibitory substance is send in the direction
of the basal buds. The reason why the apical bud grows out
first, would be that it is the first bud which is freed from this
substance. In his later publications Loeb (1918, 1920) returns
again to his first opinion, that the inhibitory influence of the
growing stems or buds on the development of other shoots or
buds is due to the automatic attraction of the material for growth
by the stems or buds which grow out first.

Appleman (1918, 1918a), studying the growth of potato sprouts,
found that the buds on the apical end of the tuber grow out
first and inhibit the growth of the more basal buds. If the tuber
is cut into transverse slices the inhibitory influence of the apical
buds is removed and there is a general growth of buds over
the surface of the entire tuber. This proves that the slices still
contain sufficient growth material to produce shoots and they
were not prevented from doing so, because the terminal sprouts
had automatically attracted the limited amount of material for

Experimenting with isolated cuttings of Citrus medica Reed
and Halma (1919) found that the dominant influence of the
developing buds nearest the apex may be prevented from
reaching lower buds by notching the phloem layers just above
each bud. The experiments of Appleman and Reed and Halma
support the ear Her view of Loeb (1917a), that the shoots deve-
loping nearest the apex form a substance which is capable of
inhibiting the growth of other buds.

Child and Bellamy (1919, 1920) succeeded in blocking the
inhibiting action of the growing tip of Phaseolus upon other
buds, or of a leaf of Bryophyllum upon buds of other leaves,
by a zone of low temperature. 2 cm or more in length of the
stem or petiole was surrounded by a coil of tubing through
which a current of water flows at a temperature of 2,5 to 4° C.
In their opinion this block does not prevent the flow of water
and nutritive substances and the attempt to interpret this inhi-
bition solely in nutritive terms, is therefore highly improbable.
They conclude from their experiments that the inhibiting action
in its passage from point to point depends upon the metabolically
active protoplasm. Why, in their opinion, this should exclude
the transport of an inhibiting substance, is not clear, as the
movement of inhibiting substances might itself depend on the
activity of living cells. By killing part of the stem of Phaseolus
by means of steam, Harvey (1920) succeeded in bringing about
the same effect as Child and Bellamy, namely the growing out
of the axillary buds just beneath the dead zone, although the
part above it remained alive.

By cutting potato tubers lengthwise into pieces and soaking
them 2 hours in 4 per cent thiourea (NHgCSNHa) Denny (1926)
succeeded in disturbing the apical dominance of sprout formation.
In many cases it was found that the apical buds of tubers treated
with thiourea did not grow, but that growth first started in buds
towards the basal end. The growth of the apical buds then was
inhibited by the growth of the basal buds that had started first;
for the apical buds started growth at once when cut off from
these tubers and planted separately.

In the investigations treated in this section it was tried to
find an explanation for the phenomenon of correlative inhibition
of lateral buds and shoots by assuming an organ forming sub-
stance, a nutritive exhaustion, an inhibiting substance or the
transmittance of some physiological process. The later experi-
ments are strongly in favour of an inhibiting substance; curiously

enough, however, most of the experiments do not solve the
question, whether a nutritive exhaustion or an inhibiting sub-
stance brings about the correlation. Experiments, which in the
opinion of some investigators clearly prove one theory, are
interpreted by other scientists in just the opposite way. Most
experiments can be explained in favour of the one theory as
well as of the other and we get the impression that it only
depends on the investigator's original point of view which inter-
pretation he will give of his experiments. It is only in the light
of the investigations on the role of auxin in these correlation
phenomena, that the early experiments become comprehensible.

A profound study of the correlation between leaf and axillary
bud was made by Dostbl (1909, 1926) in Scrophularia nodosa.
For his experiments he used isolated stem cuttings consisting of
one pair of opposite leaves and a piece of internode above and
below the node; the bases of these „pairs of leavesquot; were put
in water. After cutting away one of the two leaves the bud in
its axil began to develop while the one in the axil of the intact
leaf did not. The same result could be obtained by covering
one leaf with black paper. Simultaneously with the development
of the axillary bud of the amputated leaf there was a strong
root-formation at the base of the stem at the half of the intact
leaf; on the side where the leaf had been removed no roots
appeared. If botri axillary buds are brought to development one
of them will generally grow out much faster than the other. As
DosTaL has pointed out, a similar correlation is found between
them, as between terminal and lateral shoots. The one which
grows fastest inhibits the growth of the other. Once the axillary
buds having grown out, the inhibiting influence of the leaf is
of little importance.

By longitudinally splitting at the base the internode of a „pair
of leavesquot; of which one leaf had been removed and putting the
basal half of stem, connected with the intact leaf, in a 0,2 %
Knop's nutrient solution or in 1 n glucose, the other half with
the removed leaf being put in water, the inhibiting influence
of the intact leaf on its axillary bud was reduced by the Knop-
solution, but was increased by the glucose. Full-grown leaves
have the strongest inhibitory influence; this influence decreases
with increasing age. In cuttings with two pair of leaves, a leaf
is also capable of inhibiting an axillary bud above or beneath it.

According to DosTaL the assimilation products of the leaf regu-
late the growth of the axillary bud; therefore the leaf must be
able to function normally and must not lack nutritive substances,
light and water. He leaves undecided whether the inhibiting
influence may be due to a specific inhibiting substance formed
in the leaves during the assimilation.

We owe an important series of investigations on the correlative
inhibition of the growth of axillary buds and shoots to Snow
(1925, 1929, 1929a, 1931, 1931a, 1932). Snow (1925) split Phaseolus
seedlings longitudinally from the roots up to about 2 cm of the
epicotyl; the halves were then immediately bound tightly together
again. One of the halves was completely isolated from the upper
part by a transversal cut passing from the top of the split out
to the side of the epicotyl. Further as a control part of the
plants was decapitated. Then the bud in the axil of the cotyledon
of the isolated halves grew out much more slowly than that of
isolated halves of decapitated controls. Yet it was not likely
that in the non-decapitated plants the growing apex could with-
draw any nutritive substances from the isolated halves. Since
the inhibition did act across a watery gap. Snow concluded that
it was very likely that it was conducted by the diffusion of a
soluble substance. By ringing the epicotyl down to the wood,
the inhibition was not yet interrupted, but only weakened if
the axillary bud was left connected only by the pith with the
main apex.

Snow (1929) also made the following interesting experiment.
Young seedlings of Vicia Faha were decapitated in the epicotyl,
so that the two axillaries grew out. Of these the shorter one
was decapitated above its second leaf and a bud was allowed to
remain only in the axil of one of the two leaves of this shoot.
The remaining bud did not grow out, but when the other shoot
was also decapitated this bud grew out strongly. If the base of
the shorter shoot was killed by scorching, the axillary bud above
this zone was still inhibited by the apex of the longer shoot.
If the longer shoot was decapitated too, no inhibition occurred.
Snow concluded from this experiment that an inhibiting sub-
stance, coming from the apex of the longer shoot, was drawn
up through the dead zone with the transpiration stream. In later
experiments Snow (1929a) found that in seedlings of Pisum
sativum the inhibiting effect exerted by the shoots upon their
axillary buds comes from three or four of the developing leaves.
Likewise as from the experiments of DosTaL (1909, 1926) it
appears that the leaves are the source of the inhibition. In Pisum

sativum the leaf begins to inhibit at a length of 2 to 2,5 mm
and it continues to inhibit strongly from the length of 3 to 15
mm; at about 20 mm the inhibition effect begins to fall off
rapidly and at the fnial length of about 45 mm the leaf no
longer inhibits at all or only very sHghtly. The strength of
inhibition increases with the length of the interiacent stem, for
in isolated decapitated pea-seedlings single developing leaves
inhibit axillary buds that are from 70 to 100 nam below them
more strongly than similar leaves in similar seedlings inhibit
buds that are only from 5 to 15 mm below them (Snow, 1931).
This should make clear, why axillary buds of pea-seedlings grow
out to a certain length, before they are stopped by inhibition.
The axillary buds are at first not inhibited because they are
too close to the developing leaves in or near the apical bud.
They therefore grow until the growth of the main shoot separates
1liem far enough from the developing leaves that inhibition is
strong enough to stop them. Snow does not say, how he explains
this increasing inhibition with increasing length of interiacent
stem.

By decapitating young pea-seedlings in the epicotyl Snow
(1931a) could obtain plants with two shoots springing from the
axils of the cotyledons. If in such „two-shoot plantsquot; one of the
shoots has its leaves removed, until only those, 1 mm long or
less, remain, it is rapidly arrested in growth and finally killed,
whereas similar simple shoots similarly defoliated grow on
rapidly and indefinitely. Snow concluded that in these „two-shoot
plantsquot; the inhibiting influence coming from the two shoots
counteract each other. If one of the shoots is defoliated or other-
wise weakened, the influence coming from the other shoot travels
up into it and arrests and kills it. Why this influence should
travel acropetally in the defoliated shoot, while it normally travels
basipetally in the intact shoots. Snow does not make clear.

In a following publication Snow (1932) recalls the fundamental
investigations of Jost (1893) who showed that, as a rule, cambial
growth in stems only takes place under the influence of growing
leaves and further, that their influence travels only downwards.
Snow found that in Vicia Faba strips of mature stem survived
and grew in thickness if they were attached by the top, so that
they received the downward-moving cambial stimulus; but if
attached by the base, they died. The killing of the defoliated
shoot in „two-shoot plantsquot; Snow now explains in this way, that
the young leaves transmit downwards, among other growth-
regulators (either growth promoting or inhibiting), the cambial

stimulus, which overruns the inhibition by other factors in the
parts which it reaches. It does not penetrate into lateral shoots
or buds, however, whereas the inhibiting influence does pene-
trate into them. The growing leaves protect their shoot bij means
of the canlbial stimulus of being inhibited by another shoot. It
seems a little surprising, however, that the growing leaves
should transmit downwards growth promoting as well as -inhi-
biting influences, of which the latter could also travel upwards.

a. The „directquot; theory of Thimann and Skoog and the
„indirectquot; theory of Laibach.

The investigations of DosTaL and Snow discussed in the pre-
ceding section made Thimann and Skoog (1933, 1934) assume that
the correlative inhibition might be caused by the growth sub-
stance which was first demonstrated to occur in Avena-coleop-
tiles by Pabl (1919), later quantitatively determined by Went
(1926, 1928) and first isolated in a pure form by Kögl and
Haagen Smit (1931) '). Using the diffusion-method and the
Avena-test as described by Went (1928) with the procedure, size
of agar blocks etc. as given by Dolk and Thimann (1932) they
determined the production of growth-substance of the terminal
and lateral buds of Vicia Faba. The amount of growth substance,
produced by the terminal bud was considerable (about 30 plant
units per hour); in the undeveloped lateral buds (3,5 mm in
length) there was little or no production, but during active
growth they produced it in considerable amounts (about 20 plant
units per hour). lîie growth-substance was produced by the
leaves in smaller quantities than by the developing lateral buds,
the amount decreasing with the age of the leaf. The production
of growth substance thus closely parallels the bud-inhibiting
effect found by dostal and by Snow.

Further they applied to the top of decapitated seedlings of
Vicia Faba agar blocks with growth substance, which were
renewed every 6 hours. The growth substance was obtained from
the ether extract of the culture medium of Rhizopus suinus
under the conditions described by Dolk and Thimann (1932).

For a survey of the nature of this growth substance or auxin and its
role in plant growth I may refer to the excellent reviews of Boysen
Jensen, Avery and Burkholder (1936) and of Went and Thimann (1937).
=) The „plant unitquot; of Dolk and Thimann (1932) is that amount of
growth substance which when applied unilaterally to decapitated Avena-
coleoptiles in a 10,7 mm-' block of agar causes 1° curvature under the
standard conditions.

The continued application of agar blocks with 1670 plant units
growth substance per cm' suppressed the development of lateral
buds to about the same extent as does the tip in intact plants.
At the same time elongation of the stem was obtained by ap-
plying agar blocks with 800 plants units to decapitated and defo-
liated pea-plants and by submersing isolated preparations in a
growth substance solution of 100 plants units per cm'. These
experiments leave no doubt that an auxin-like substance(s) is
the inhibitor of bud-development in Vicia Faba.

The fact that more growth substance had to be applied than
diffused from the tip (1670 against about 180 plants units per
6 hours), they ascribed to inactivation of the growth substance
by wound substances and loss in non-transporting tissues. To
explain the fact that a growth promoting substance might act
as an inhibitor Thimann and Skoog supposed that the growth
substance produced by the terminal bud reaching the lateral
buds, prevented them in their own production of growth sub-
stance. As soon as the terminal bud is removed, this supply
of excess growth substance ceases and the buds now commence
to synthesize growth substance on their own account and there-
fore develop.

The same should occur in the physiological regeneration of a
tip in a decapitated Avena-coleoptile. In the opinion of Thimann
and Bonner (1933) the presence of growth substance in suffi-
ciently high concentrations prevents the production of growth
substance in the lower zones of the coleoptile, and only when
the supply is cut off by removal of the tip, production of growth
substance occurs in the next lower zones.

In the case of the .Auena-coleoptile, however, Thimann and
Bonner (1933) could show that there was a linear relationship
between growth substance added and growth produced. But
Thimann and Skoog do not give any explanation as to why, if
growth substance reaches the lateral buds, these laterals are
unable to use it for their development and are depending on
growth substance of their own synthesis. Nor does their theory
explain the inhibition of one developing bud by another, observed
by them too. For from their own experiments they conclude that
the transport of growth substance in Vicia-stems is apparently
a polar phenomenon of the same type as that found in Avena-
coleoptiles by Went (1928) and van der Weij (1932). It is there-
fore not probable that grovsrth substance from the stronger deve-
loping bud travels up the stem of the shorter one.

to the top of the decapitated epicotyl of Vicia Faha inhibit the
development of the cotyledonary buds. Living pollinia secrete
considerable amounts of growth substance, as was shown by
Laibach before (1932). Laibach observed a considerable growth
in thickness and length of the decapitated stem to which the
growth substance was applied and he therefore supposes that
the inhibition is not due to a direct action of the growth sub-
stance on the lateral buds, but that it first takes part in some
growth process in the main stem and that this growth then
secondarily inhibits the buds.

Against the experiments of Laibach this serious objection may
be raised, that the growth substance is supplied quot;in extra-
ordinarily high concentrationsquot; as he himself says. For this
reason too the swellings and thickenings, which are the results
of this application, cannot be called normal and are by no means
a reliable indication for what happens in the intact plant.

To test the possibility that the inhibition was not due to the
growth substance itself but to a special inhibitor present in
their impure preparations Skoog and Thimann (1934) repeated
their earlier experiments with crystalline preparations isolated
from urine and other sources by Kogl^ Erxleben and Haagen
Smit (1934). An aqueous solution of these preparations was in-
troduced every 8 hours into small paraffine cups which were
moulded unto the cut surface of the stem of Vicia Faba. Of the
three isolated growth hormones, auxin-a, auxin-b and hetero-
auxin, auxin-a had lost most of its growth promoting activity
and produced no inhibition, but auxin-b and hetero-auxin
showed to be at least as active in causing inhibition as the
impure preparation of Rhizopus suinus, when used in the same
concentrations in growth promoting units (1000, 3000 and 5000
plants units per cmquot;).

The correlative inhibition of leaves on the development of
their axillary buds, was investigated closer by UnRova (1934) in
the light of what had meanwhile become known about the role
of growth hormones in these phenomena. If he cut off both
leaves of an isolated quot;leaf-pairquot; of Bryophyllum and then
replaced one of them on its petiole, interplacing a thin layer
of agar, this leaf would exert the same inhibiting influence on
its axillary bud as if it had been left intact. The same results
may be obtained by placing the leaf on agar and then applying
the agar block to Ijhe cut petiole. When this agar block was
placed unilaterally on decapitated Avena-coleoptiles, it gave a
distinct growth curvature. The substances, diffusing from the

developing buds of Syringa vulgaris, tiie tips of Avena- and Zea-
coleoptiles and flowerheads of Bellis perennis, have the same
inhibiting influence on the axillary buds of Bryophyllum. Though
UHROvâ gives these substances the name of inhibiting substances,
he yet draws the obvious conclusion that these substances are
identical with growth sulbstances.

Boysen Jensen (1935) mentions in his book quot;Die Wuchsstoff-
theoriequot;, that he, ascribing the dormancy of resting plant-organs
to a lack of growth substance, filled the hollow internodes of
Forsythia with growth substance solutions or made this fluid
flow slowly through twigs of Salix, Syringa and Aesculus. But it
was not possible to observe any quot;forcingquot; effect in any of these
experiments made during winter.

By applying to the decapitated stem some lanolin paste with
growth substance extracted from orchid pollinia or urine as
done by Laibach (1933), Müller (1935) succeeded in inhibiting
the development of the lateral buds in a great number of plants
which as yet not had been tested in this respect. She obtained
a marked, though not complete, inhibition in Linum, Pisum,
Antirrhinum, Godetia, Phaseolus, Zinnia, Sinapis, Helianthemum
and Tradescantia; no inhibition took place in Impatiens, Polygo-
num and Tropaeolum. In the decapitated shoots there appeared
a strong growth connected with a great nrmiber of cell divisions
under the influence of the growth substance supplied. Like
Laibach, Müller too thinks that the renewed growth phenomena
are responsible for the inhibition of the axillary buds. The fact
that she could not obtain a complete inhibition in her experiments
Müller explains by assuming that when the renewed growth has
finished, the inhibition stops too. And indeed, with Vicia Faha
she could obtain an almost complete inhibition by repeated deca-
pitation and by continuously applying growth substance, which
again and again caused new cell divisions. In the intact plant,
however, these cell divisions will not occur to the same extent
and it seems to me that they had better be considered as an
attendant phenomenon in this abnormally high supply of growth
substance.

From some experiments with an application of lanolin paste
by the Laibach (1933a) method with growth substance prepared
from urine, Czaja (1935, 1935a) draws the conclusion, that a
stream of growth substance flowing in a given direction in a

parailelotropic organ will morphologically polarize the cells of this
organ. The swellings and growth inhibitions, which he observes
in the case of supply of growth substance at right angles to the
longitudinal direction of a stem or root, are due, in his opinion,
to the direction of this supply, by which the cells can only enlarge
themselves in a radiar direction. This leads him to assume that
the growth inhibiting action of growth substance on roots is
due to a mutual weakening of two opposing streams of growth
substance, of which each in itself is again growth promoting.
If one stream is stronger than the other, the cell in its polar
behaviour will be mastered by the stream of the highest concen-
tration. The correlative inhibition of the axillary buds by their
leaves too, he explains in this way, namely that the stream of
growth substance coming down from the leaves is opposed to
the probably very weak one coming from the buds and so inhibits
it altogether.

The existence of two opposite streams of the same substance
in one and the same organ, even in the same cell, however, has
not been proved by Czaja. It is not clear, how to imagine such
a transport.

Skoog (1935) promoted the outgrowth of lateral buds by a
treatment of the plant with X-rays. He showed that, when the
apical end of a growing young Pisum-plant was exposed to
X-rays, the production of auxin by the terminal bud was inhi-
bited. Parallel with this the growth of the main stem was reduced
and the buds in the stipules began to grow rapidly.

By treating the cut surface of decapitated Nicotiana-plants with
lanolin preparations containing a high concentration of indole-
acetic, indole-propionic, phenyl-acrylic, phenyl-propionic, indole-
butyric, phenyl-acetic or naphtalene-acetic acid Hitchcock (1935)
obtained a marked inhibition of the growth of the upper two or
three buds. As these substances as far as known play no role in
normal growth phenomena and as Hitchcock used abnormally
high concentrations (from 3 in 10' till 1 in 10), these data are of
little importance in explaining the phenomenon of bud inhibition.
They only fit in a systematic research on the relation between
structure and activity of growth promoting substances. The same
holds for the communication by Thimann (1935) that the supply
of indene-3-acetic and coumaryl-l-acetic acid in lanolin paste in
a concentration of 1 in 10' and 1 in 10^ causes a strong inhibition
of bud development in decapitated pea seedlings. Like Hitchcock
he found that the effect of the substances used was weakened
when the point of application was far from the bud, their trans-

Le Fanu (1936) then informs us of sone interesting new facts.
Bij placing single-node stem cuttings of Pisum sativum in solu-
tions of pure synthetic hetero-auxin of 2 in 10« and 4 in 10quot; she
could obtain a strong inhibition of axillary buds. By placing intact
shoots with their bases in hetero-auxin solutions of 2,5 in 10'
and 5 in 10^ the growth of the stem was inhibited too. The same
result was obtained by inserting lanolin paste containing 5 in 10'
hetero-auxin in a longitudinal split of the 4th internode of the
stem, the growth of the 5th internode above it then was retarded.
If the leaves of the plants were removed the same result was
obtained with 5 in 10» hetero-auxin paste; but in plants with
intact leaves hetero-auxin 5 in 10» hardly had any effect. As
Snow in 1931 Le Fanu explains this last experiment in this way
that the leaves protect a stem against inhibition. Of what nature
this protection is, she leaves undecided, however. Nor can she
explain the outgrowth of the buds in the axils of the leaves
2 and 3 after applying hetero-auxin paste 5 in 10' into the split
in internode 4. She showed, that hetero-auxin of about the same
concentration yet can exert a growth promoting influence by
application of hetero-auxin paste 1 in 10' to the cut surface of
decapitated and debudded pea seedlings in the dark. She then
obtained an acceleration of the growth of the youngest internodes.
Le Fanu concluded from these experiments that the nature of
auxin action, whether it is acceleration or inhibition is determined
by the position of the auxin source relative to the organ to be
affected. Travelling morphologically downwards auxin accelerates
growth, coming from a morphologically basal part it inhibits.

By placing parts of the stem from both the shoots of quot;two-
shootquot; pea plants excentrically on Auena-coleoptiles Le Fanu
obtained after three hours strong curvatures with the stem
parts of the stronger shoots, but no or scarcely any curvature
with the same parts of the inhibited shoots. This absence of
auxin in the inhibited shoots suggests that no auxin is
transported into them in upward direction and therefore the
inhibition cannot be due to a direct action of auxin. The
conclusion is reached by Le Fanu that the inhibition is probably
a secondary process which originates from some primary process
promoted by auxin in the inhibiting shoot. In her opmion not
the abnormal stem swellings and cell divisions as found by
Laibach (1933), but the cambial divisions shown by Snow (1935)

as caused by auxin, might be considered as this primary reaction.
However, in this case one meets the same difficulty as in the
theory of Czaja (1935, 1935a): one has to assume that in a two-
shoot plant from each of the two shoots an inhibiting action
will start which will travel upwards into the other shoot. In
each of the two shoots therefore two of these effects will be
transported in opposite directions, while the one from the fastest
growing shoot will win.

The experiments of Le Fanu are confirmed and extended by
Snow (1936). By putting a ring of concentrated hetero-auxin
paste (5 in 10-!) round the stem of pea seedlings, deprived of their
leaves, close below one of the growing internodes, the elongation
of the internode was at first accelerated and then strongly and
increasingly retarded. When pea shoots, deprived of their youngest
leaves except one at the top of the 4th internode, were placed
with their bases in a hetero-auxin solution of 5 in 10' the 4th
internodes were strongly retarded, but only if they were not
more than about 5 mm long at the start. If, however, they were
about 8 mm long at the start, the stage which normally comes
just before they start their rapid elongation, they are never
retarded at all. Snow concluded that the retardation of very young
internodes by hetero-auxin drawn up with the transpiration
stream is probably brought about in a way different from that
by hetero-auxin paste applied externally below; the retardation
by hetero-auxin in the transpiration stream probably being more
a direct action of hetero-auxin, the retardation by hetero-auxin
paste an indirect phenomenon.

The researches of Le Fanu (1936) and Snow (1936) are of
importance since we have to assmne that a rather high concen-
tration of auxin is present at the base of an inhibited bud or shoot
in an intact plant too, coming from the inhibiting shoot. However,
after the fundamental researches of van der Weij (1932, 1934)
the general opinion is that the transport of auxin in Aveiia-
coleoptiles is strictly polar from tip to base. Later on this basipetai
transport was found in several other organs such as stems of
Elaeagnus (van der Weij, 1933), hypocotyls of Raphanus (van
Overbeek, 1933), stems of Vicia Faba (Thimann and Skoog, 1934),
hypocotyls of Lupinus (Dukman, 1934), stems of Coleus (Mai,
1934, Gouwentak and Hellinga, 1935), leaf-veins of Nicotiana
(Avery, 1935). However, the polarity of this transport was denied
by other investigators. For it appears from the researches of
Zimmerman and Wilcoxon (1935) and of Hitchcock and Zimmer-
man (1935) that hetero-auxin and other growth promoting sub-

stances can be transported in acropetal direction in stems of
tobacco, tomato and marigold plants. Laibach and Fischnich (1936,
1936a) proved the same for leaves of Coleus and for tomato
plants. Snow (1936) for Auena-coleoptiles and hypocotyls of
Helianthus and Jost and Reisz (1936) for Auemi-coleoptiles too.
An objection to the last mentioned researches is, however, that
the growth promoting substances were supplied in unphysiolo-
gically high concentrations. One has to expect that these sub-
stances supplied at the base are taken along with the transpira-
tion stream, but anyhow this is no proof against the conception,
that in the intact plant the auxin is transported mainly in basal
direction.

For the understanding of the correlative inhibition of lateral
buds and shoots the investigations of Schwanitz (1936) in rhi-
zomes of Lathyrus and Agropyrum are important. If the rhizome
is cut into pieces directly after removal of the plant, each of
the pieces will form the same number of shoots, but the longer
one waits to divide, the stronger the regeneration will be restric-
ted to the apical parts. Schwanitz sets up the hypothesis, that
the growing-out of buds is brought about by a substance, trans-
ported polarly to the apex, while it was equally distributed over
the rhizome before. He supposes that a growth substance is
implied.

DosTaL (1936) did some work on the petiole of the cotyledon
of soaked seeds of Pisum sativum. He found that the young
epicotyl inhibits the elongation of the petiole of the cotyledon
only slightly, while absolutely inhibiting the growth of the
axillary buds of the cotyledons. The cotyledons too inhibit the
growth of their axillary buds. The radicle however, inhibits the
elongation of the petiole of the cotyledons very strongly, but
promotes the growth of their axillary buds. If, for instance, the
base of the radicle is cut on one side after the decapitation of
the epicotyl, the axillary bud on the intact side of the root will
grow out stronger than on the side above the cut, the petiole
of the cotyledon on the intact side staying behind in growth to
the one above the cut.

To explain this behaviour, a closer, quantitative examination
is wanted of the role played by auxin in these phenomena. In
connection to the later theory of Went (1936), however, Dostbl's
communication on the role of the radicle in the development
of the axillary buds is of importance.

The removal of the epicotyl and of one of the cotyledons in
pea seedlings results in a strong development of the bud in the
axil of the amputated cotyledon. Plch (1936) succeeded in
inhibiting this outgrowth by applying to the cut surface some
lanolin paste with 2 in lO' hetero-auxin and other growth promo-
ting substances. The inhibition actually decreases with lower
concentrations and when the application is made at a greater
distance.

From some later experiments of DosTaL (1936a) with isolated
pieces of tubers of Scrophularia nodosa it appears too that buds
in the vicinity of intact roots develop faster as other buds in the
vicinity of which the roots were removed.

In his quot;Allgemeine Betrachtungen über das Auxinproblemquot;
Went (1936) devotes a section to bud inhibition and describes an
experiment with decapitated dark-grown pea seedlings placed
with their roots in a 2 per cent saccharose solution. By the removal
of the roots the growth of the developing axillary buds is
strongly inhibited and the same happens, but to a less degree,
when the cotyledons are removed. In non-decapitated seedlings
the removing of the cotyledons causes a complete inhibition of
the leaf growth, while the removal of the roots inhibits the
growth to a less degree. From this Went concluded, that for
the elongation of the stem and for the growth of the axillary
buds in decapitated plants at least two factors are wanted, besides
auxin. The first factor is chiefly necessary for cell elongation and
is produced in the roots, whilst the other generally stimulates or
causes the leaf- and organ growth. The auxin directs the transport
of these specific growth factors to the production center of auxin.
So, under normal conditions, these substances are all transported
to ' the terminal bud, but if the auxin production ceases by
decapitation or by some other reason, the stream of specific
growth factors in that direction is stopped. The greater auxin
production of the lateral buds then draws this stream to them-
selves; so they can develop.

This quot;diversion theoryquot; of Went, as Snow (1937) has
called it, in fact includes two older theories, viz. that
of Sachs (1880, 1882) about the existence of specific organ
forming substances and that of Goebel (1903) and Loeb
(1915) on the automatical attraction of the material for growth
by the stems or buds which grow out first. To these theories
the new hypothesis has been added that it is the auxin which
brings about this attraction. Apart from the hypothetical cha-
racter of this theory, it does not give either an explanation of

the fact, why in the intact plant no or very little auxin is
produced by the lateral buds, whilst this auxin production is
immediately increased as soon as the terminal bud is eliminated.
If the auxin is really the initial phase of a series of processes,
it should be made clear first, why in one case no auxin is
produced and in another it actually is.

From the above-mentioned experiments of Schwanitz, Dostol
and Went it appears, however, that a factor necessary for bud-
and shoot development is transported acropetally upwards from
the roots or cotyledons.

e. The retardation of leaf development and the branching
habit as related phenomena.

In the young basal rosette of Solidago sempervirens one leaf
is rapidly elongating at a given time and then retards the deve-
lopment of the younger leaves. By removing this leaf Goodwin
(1937) could obtain the elongation of the next succeeding leaves,
but he could reproduce the retarding effect by applying hetero-
auxin in a lanolin paste at a concentration of 2 in 10* to the
petiolar stub of such an amputated leaf. The limitation in size
of the leaves was brought about by an inhibition of cell enlarge-
ment. Diffusions from the cut bases of rapidly growing leaves
surpassed in quantities of auxin those from leaves at any other
stage. The retardation is, therefore, probably due, to an excess
production of auxin by the inhibiting leaf.

In the young basal rosettes of Solidago rugosa no retardation
of succeeding leaves occurs. Maximum diffusions of auxin from
cut leaf bases were approximatively one-half as large as those
from leaves of Solidago sempervirens. Hence Goodwin suggests
that in these plants the production of auxin is too small to
cause periodic retardation.

No doubt this interesting phenomenon, as Goodwin notes too,
is of the same nature as the correlative bud inhibition. Whether,
however, it is a direct action of auxin as Thimann and Skoog
(1934) assume, seems to be questionable to him. For in that
case polarity would not yet have become established in small
buds and in very young leaves as the auxin must be transported
into them from the older leaves below.

Delisle (1937) showed that in two species of Aster, Aster
novae-angliae and Aster multiflorus, of which the former has
relatively few branches and the latter is more branched and
bushier in habit, production of lateral buds and branches can
be inhibited by applying hetero-auxin in lanolin paste 2 in 10'

to the cut ends. The rate of lateral bud development in decapi-
tated plants in which the five young leaves had been removed
was consistently greater than that in decapitated controls with
intact leaves. Diffusions indicated that the tip of Aster multi-
jlorus produces only approximatively 74 per cent as much auxin
as does that of Aster novae-angliae, and that of the hybrid only
84 per cent as much. Diffusions taken at varying distances from
the tip showed a concentration gradient which is greatest at
the tip, decreasing rapidly at the region of elongation below the
tip and falling off gradually below this point. Delisle concluded
from his experiments tfiat the problem of branching habit in
these two species of Aster is largely correlated with the diferen-
tial production of auxin by the terminal bud and the growing
young leaves. Aster multiflorus producing less auxin, has
abundant lateral buds and branches, while Aster novae-angliae,
producing considerable more auxin, has correspondingly little
branching.

In this connection we must also refer to some previous
investigations of van Overbeek (1935) on the dwarf type in corn
and of Zimmermann (1936) about tiie distribution of auxin in
trees in space and in time. Van Overbeek (1935) investigated the
amount of auxin given off by coleoptiles of the normal corn and
of the nana-form. He found, that the amount of auxin, given off
by nana, was less than that given off by normal plants, this
being probably a consequence of a higher destruction of auxin
in nana. This smaller amount of available auxin will also result
in a smaller growth in nana than in the normal plant. But if
the dwarf growth in plants must be generally ascribed to a
smaller amount of available auxin, it becomes clear — in connec-
tion with the above-mentioned investigations especially those of
Deslisle (1936) — that these dwarf types on the whole are also
more strongly branched and bushier in habit than normal plants.

Zimmermann (1936) determined in the same way the auxin
content of buds and shoots of different trees by means of
diffusion in agar slices and tests on Auena-coleoptiles. He found,
that dormant buds contain no auxin, but that this amount rapidly
increases when the buds begin to sprout, to decrease again
slowly afterwards. Buds from the upper parts of the tree give
off more auxin than buds in the same developing stage more
at the base. He also finds a very high auxin content in the
terminal bud of Aesculus hippocastanum, Acer pseudoplatanus,
Fraxinus excelsior and of various conifers, whilst the auxin
content of the lateral buds is lower and rapidly decreasing

towards the base. Parallel to this, the growth rate of the terminal
shoot of these trees is much greater than that of the lateral
shoots. zimmermann concludes, that the high auxin production
of the terminal bud clearly inhibits that of the lateral buds. On
the other hand in the case of Tilia the growth of lateral shoots
is much stronger than that of the terminal shoot, but there the
auxin content of the lateral buds is higher than that of the
terminal bud. From these highly important investigations follows
that the external architecture of trees can be ascribed to the
difference in auxin production of terminal and lateral buds.
The question which rising now is: what is the cause of this
difference in auxin production?

f. The controverse between the quot;directquot;, the quot;indirectquot; and
the quot;diversionquot; theory.

Snow and Snow (1937) showed that one of the effects of ap-
plying hetero-auxin — in lanolin paste at a concentration of 5
in 10' — to a part of the growing apex of Lupinus alhus is an
abnormal enlargement of the leaf primordiinn and axillary bud,
which subsequently arises from that part. It appears, therefore,
that the direct effect of hetero-auxin in bud growth is a promo-
ting one.

Nagao (1937) finds an inhibition of the elongation of Helian-
t/ius-hypocotyls by application of hetero-auxin lanolin pastes at
a concentration of 4 in 10' till 5 in 10* to the cut surface of
cotyledons whose upper halves have been removed. Le Fanu
(1936) however, did only find an inhibition of th- growth of
young internodes of non-decapitated pea seedling by apphcation
of hetero-auxin paste 5 in 10= to a part of the stem morphologi-
cally below and a growth acceleration by application of hetero-
auxin paste 1 in 10' to the upper ends of decapitated dark-
grown seedlings. Nagao considers the mhibition found by Le
Fanu and by himself as due to an excess amount of auxin in
the effected zone, and notes that the decapitation may play an
important role in Le Fanu's experiments as it will reduce the
amount of natural auxin present. However, the fact that Le Fanu
found a stronger inhibition by the removal of the leaves cannot
be explained by an excess amount of auxin. As neither Le Fanu
nor Nagao did determine the auxin content in the zones affected,
this question must be left undecided.

In their review on phytohormones Went and Thimann (1937)
point out that the influence of factors other than auxin may
explain why some buds have a greater tendency to develop

than others. So they try to explain the increase with distance
of the inhibition exerted by young leaves of Pisum in Snow's
experiments (1931), by assuming that the tendency to grow out
is greatest in the basal buds. They conclude, that the mechanism
of bud inhibition can probably not be understood until the
fundamental mechanism of auxin action on the cell, and the
role of other factors in bud growth are better revelled.

One will agree with Went and Thimann that undoubtedly other
factors as water, light and food, effect the development of lateral
buds and shoots too. Since, however, Thimann and Skoog (1934)
had proved quite plainly that auxin brings about the correlative
inhibition of lateral buds and shoots, we must first try to eluci-
date which role auxin plays in this phenomenon.

Previously DosTaL (1926) already found that the leaves of
Scrophularia nodosa inhibit the development of their axillary
buds. Also in this case an action of auxin seems evident. Recent
experiments of DosTaL (1937) showed that this is the case in-
deed. He cut off both leaves of a leaf-pair of an isolated section
at the base of the stem, and to one of the cut surfaces he
applied hetero-auxin paste 5 in lO'', to the other one plain lanolin.
The growth of the axillary buds was inhibited at the side where
hetero-auxin was applied. Curiously enough, the development
of higher axillary buds in similarly treated stems with more
leaf-pairs was promoted by the application of hetero-auxin paste
of the same concentration. According to DosTaL the different
age of the implied sections causes this different behaviour.

Later Thimann (1937) communicates some new experiments
with Pisum seedlings. By applying lanolin paste with hetero-
auxin at concentrations of 4 in 10quot; till 4 in 10' to decapitated
dark-grown seedlings a marked inhibition of the development
of lateral buds was obtained. This, however, was not accom-
panied, as Laibach (1933) had postulated, by any compensating
increase of growth elsewhere in the plant and involved a real
decrease in total dry weight.

According to the theory of Went (1936) the auxin would act
by attracting to itself no nutrients but specific factors for bud
growth. Thimann believes, one of these factors is to be a special
substance, called by Went quot;caulocalinequot;, coming from the roots
and decidedly different from auxin. If auxin is supplied to the
bud itself, a kind of attraction will bring the bud factors to the
bud and, instead of inhibiting, auxin will accelerate growth.
Direct application of hetero-auxin in lanolin at concentrations
of 4 in 10quot; till 4 in 10' to young lateral buds, 1 mm in length.

of decapitated seedlings, however, did inhibit their growth as
compared with controls treated with plain lanolin. The higher
concentrations, however, produced swollen buds and there was
a marked increase in the dry weight of the buds per unit of
length. These results thus contradict the above mentioned ones
of Snow and Snow (1937) and do not endorse Went's theory.

Thimann then points to the parallel behaviour of buds and
roots, which are both inhibited by auxin. However, as had been
proved previously by Faber (1936), Fiedler (1936), Amlong
(1936), Thimann (1936) and Geiger-Huber and Burlet (1936),
very low concentrations of auxin accelerate root growth, the
response of roots to different concentrations of auxin thus
showing an optimum curve. The parallel behaviour of roots
and buds to auxin inhibition and the fact that very dilute auxin
solutions increase root elongation make Thimann suggest that
roots, buds and stems all behave in a comparable way; their
growth being inhibited by relatively high and promoted by
relatively low auxin concentrations. Buds, therefore, in their
response to auxin also should show an optimum curve and this
curve should fit in between those of stems and roots; the nor-
mal auxin concentration in the stem of the growing plant being
such as to stimulate the stem and to inhibit the buds.

This theory of Thimann (1937) has the advantage of putting
the various observed effects of auxin in roots, buds and stems
on a uniform basis. He did not prove, however, that the amount
of auxin in the inhibited buds is large indeed; on the contrary
from the experiments of Thimann and Skoog (1934) follows, that
the amount of auxin present in the undeveloped lateral buds
in Vicia Faba is very low. He cannot explain either the inhibition
of lateral shoots, a phenomenon closely related to that of the
inhibition of lateral buds. In that case, according to Thim.-vnn,
the inhibition depends rather on competition for some other
factor such as water or a second factor (caulocaline) which
comes from the roots. Bud inhibition and shoot inhibition are
not likely to be explained in two different ways, however.

In a recent publication Snow (1937) also raises some serious
objections against the quot;directquot; theory. In one of his experiments
from some quot;two-shootquot; pea seedlings one of the shoots was
decapitated just below the second leaf from the base. The
decapitated shoot was placed inversely with its upper cut end
in a little water in a glass tube. If the second shoot was left
intact, the axillary buds at the first leaf nodes of the shoots in
the tubes did not grow at all, but in decapitated controls they

grew vigorously. Snow concluded from this, that in these plants
the inhibition travelled from the intact growing shoots up
through the cotyledonary nodes to the buds of the decapitated
shoots, even against the transpiration stream.

In a following experiment young seedlings of Vicia Faha were
split longitudinally with a median split through the main root,
the cotyledonary node and upwards through the epicotyl nearly
to the first node. Then the main shoot was decapitated higher
up, above the third node, and when the two buds in the axils
of the cotyledons had grown out and formed shoots one of these
shoots was decapitated above its first leaf. The bud in the axil
of this leaf then was inhibited by the other cotyledonary shoot
across the zigzag peith of tissue connecting the shoots. The in-
hibition thus travelled down the growing shoot, up and down
through the halves of the split epicotyl and up again through
the decapitated shoot. Yet there was no sign of cambial growth
on the cut surface of the halves of the epicotyl.

From these experiments Snow concludes that the inhibiting
influence can travel where auxin cannot travel, and therefore
the quot;directquot; theory cannot explain this correlative inhibition
of lateral buds and shoots. Since further no auxin from the
growing shoots enters the epicotyl halves the inhibited bud can-
not possibly have been deprived of any substances coming up
from the half root system and cotyledon below it through any
polarizing action of auxin, as Went's theory would suggest. For
this reason Snow sticks to the quot;indirectquot; theory: the auxin
travelling down a stem promotes its growth, and the growth of
the stem then in some way inhibits the lateral buds secondarily.
As Snow indicates, the primary process promoted by the auxin in
the stem need not always be actual growth, for in Tamus com-
munis, a monocotyledon, he finds that if the tip of a shoot that
stopped growing is cut off, several of the upper axillary buds
soon grow out strongly, though in intact shoots the axillary
buds do not grow out. Yet in these shoots there is, of course,
no cambial growth and scarcely, if any, growth in thickness.
In discussing the nature of this secondary inhibiting influence.
Snow assumes that this influence must be a soluble substance
or substances of some kind. Accordingly he tried in various
ways to extract some substance or substances from inhibited
shoots to which the inhibition might be due, but up to this
moment without success.

In a recent publication Went (1938) gives evidence for the
existence of the specific factors involved in bud- and leaf-growth

postulated by him before (1936). 4 cm tops of etiolated pea
shoots were grafted on root systems (with attached cotyledons)
of the same plants or of peas of different varieties. After the
junction of the tissues, growth was resumed at approximately
the initial rate. Since stem elongation, leaf growth, stipule growth
and petiole growth were differentially affected by the pea varie-
ties used as rootstock. Went concludes that each of these pro-
cesses is influenced by a different factor or set of factors. Special
terms are suggested for these specific factors — viz. caulocaline
for a factor coming from the roots and necessary for stem
elongation, and phyllocaline for a factor indispensable for leaf-
growth and in etiolated peas coming from the cotyledon.

In connection with the results of my own experiments and
the theory set up in consequence of it, the literature treated in
this chapter will be briefly discussed again in chapter X, § 3
(p. 274). In a previous publication (Ferman, 1938) mention was
already made of some of these experiments and of this new
theory on the correlative inhibition of lateral buds and shoots.

As experimental plant I used chiefly a pure line of Lupinus
alhus. The seed was obtained from the firm of Hulleman at
Utrecht. The seeds were placed each separately in earthen pots
filled with leaf-mould. From October till April the plants stood
inside the greenhouse; for the remaining months they were
dug in under glass outside. From January till April the plants
were illuminated with a Philips' neon tube from 16h—24h and
from 6h—9h.

For some experiments seedlings of Pisum sativum, variety
quot;Kaapse groenequot;, were used, which had been grown in mould
in the green house. Young twigs taken from a shrub of Ligustrum
vulgare in the botanical garden at Utrecht served for some ex-
periments with cuttings.

For the application of auxin to the plant aqueous solutions
and lanolin pastes of pure, synthetic hetero-auxin (indole-3-
acetic acid) were used. This preparation had been obtained
from Dr. Fraenkel and Dr. Landau in Berlin-Oberschoneweide.
Germany. The solutions were made by weighing 10 mg of

hetero-auxin and dissolving it into 100 cmquot; of tap water. From
this standard solution 1 in 10* the dilutions wanted were then
prepared. The lanolin pastes were made by mixing an equal
volume of lanolin and hetero-auxin solution. The solutions and
the pastes were kept in the refrigerator and renewed every 7
to 10 days.

The application to the plant of the aqueous hetero-auxin
solutions and of the tap water to the controls was made via
the decapitated main- or lateral stem. For this purpose small
glass tubes, of about the same diameter as the stem, were
fastened onto the cut stem by means of a little rubber tube,
10 mm long. — Only in experiment 1 these glass tubes were
fixed watertightly to the outer side of the stem by means of
paraffin —. In the experiments, made in 1936, these tubes had
a length of 15 mm and a content of about 0,15 cm'; in the later
experiments they had a length of 20 mm and a content of about
0,2 cm\ Once or twice a day, in the first case generally at lOh,
in the second case at 9h and at 17h (in experiment 1 at lOh and
at 22h), these glass tubes were filled with fluid by means of a
pipette with a finely drawn-out point. Great care was taken
that no air-bubbles could prevent the fluid from entering the
stems. The fluids were absorbed regularly by the plants.

The investigations of Kögl, Haagen Smit and Erxleben (1934)
and of Heijn (1935) have made it very plausible, that the auxin
found in higher plants is auxin-a and certainly not hetero-auxin.
An application of auxin-a is therefore preferable to an applica-
tion of hetero-auxin. As auxin-a, however, could not be obtained
in sufficient quantities and as, besides, it has the disadvantage
of soon becoming inactive (Kögl, Haagen Smit and Erxleben,
1933) we, like so many other investigators (see Chapter I, § 3,
p. 187), ressorted to hetero-auxin, the effect of which on the
growth of plants apparently is, on the whole, the same as that
of auxin-a. There are some differences, however, — in the
Auena-test hetero-auxin has of the molecular activity of
auxin-a (Kögl and Kostermans, 1935), hetero-auxin is probably
transported somewhat less readily (Thimann, 1935; van Overbeek,
1936, 1936a), auxin-a is inactivated considerably by light, hetero-
auxin very little or not at all (van Overbeek, 1936, 1936a;
Koningsberger and Verkaaik, 1938) —, but on the other hand
Skoog and Thimann (1934) found no differences in activity
between auxin-b and hetero-auxin in bud inhibition in Vicia
Faba. This makes us expect that the artificial application of
hetero-auxin may give us also some information about the role

of auxin-a in the correlative inhibition of lateral buds and shoots
in the intact plant.

The auxin is extracted from the plants with ether after the
method devised by van Raalte (1937). This method is as follows.

First those plant parts of which the auxin content had to be
determined were ground very finely in a mortar together with
about an equal volume of chemically purified quartz sand and
some drops of 0,5 n sulphuric acid. As soon as the plant parts
had been crushed more or less, so much ether, freed from
peroxide, was added that the pulp was entirely submerged in
it and the grinding was continued. — The ether was freed
from peroxide by distilling shortly before 400 cm' ether over
10 g FeS04, 1 g CaO and 40 cm' HgO —. After the extraction
the ether was decanted and the extraction repeated twice with
new ether. The extract was washed twice with water, acidified
with sulphuric acid to the conversion point of congo red. Finally
the ether was evaporised over a hot water bath, till the volume
was about 5 cm-'. The rest was put in a small tube with 0,2 cm'
of a diluted buffer solution after McIlvaine. — The buffer con-
tained 0,04 mol citric acid and 0,02 mol Na2HP04; its pH was
± 5^4 —. This tube was kept in a beaker with warm water
and the evaporating ether was blown away by means of an air
current. The résidu solved in the 0,2 cm' of the buffer solution.
The water insoluble substances were removed as far as possible
by washing the preparation with petrolether. Two 3% agar slices
of 8 X 6 X 0)9 inm were added and remained in the refrigerator
in this solution overnight; the next day their auxin content
was determined.

In order to prevent the auxin of becoming inactive by illu-
mination (C. Koningsberger, 1936) as much as possible, all the
manupulations were carried out in weak orange light (filter
O.G. 2).

For the determination of the auxin content of plant parts the
extraction method is preferable to the diffusion method in which
the plant parts are placed for a certain time on agar slices. In
the diffusion method only that amount of auxin can be deter-
mined, which is given off by the plant part to the agar slice.
The rate with which this is done and the percentage of the total
amount of auxin present which is given off will strongly vary
in different plant parts. Only by extracting the auxin, it will
be possible to get an impression of the total amount of auxin.

present in the plant parts concerned. The following fact may
serve as an example: older investigators (Went, 1928; Söding,
1929) who worked with the diffusion method, could not prove
any auxin to be present in the basal part of the Averia-coleoptile
and from this fact they drew their conclusions. Later on,
Thimann (1934) being the first to apply several extraction
methods, clearly showed that auxin is present in all sections of
the coleoptile, though in the basal part less than directly under
the tip. Besides, the extraction method has the advantage, that
the auxin content of a certain part of a whole series of plants
can be determined simultaneously, whilst in the diffusion method
only the auxin delivered by small plant parts can be estimated.

The auxin content was determined by means of the Avena-
test under standard conditions, as described by Went (1928)
and improved later on by v.^in der Weij (1931). For a description
of this test method I may also refer to Boysen Jensen, Avery
and Burkholder (1936) and Went and Thimann (1937).

For the test a pure line of Victory oats {Segre hajer) was
used, obtained from the Sveriges Utsädesförenings Institution
at Svalöv, Sweden. The plants were grown in water culture in
racks for 12 plants in a dark room in a relative moisture of
95%, a temperature of 22,5° C. and an orange illumination (filter
O.G. 2). In the tables and figures the auxin content of the plants
is always expressed by the curvatures (in degrees) of the Avena-
coleoptiles. These data are the averages of 16—24 coleoptiles, the

As the reactivity of the test plants varies from day to day
and even from hour to hour (Kögl, 1933; Kögl, Haagen Smit
and van Hülsen, 1936), the figures thus obtained on different
days, are incomparable in an absolute sense. We tried to quot;gaugequot;
the curvatures, found on different days, by always comparing
them with the curvature brought about by a hetero-auxin
solution of a known concentration. But this too yielded no
uniform results. It is not improbable, that in spite of a
3 times repeated decapitation, this variability is due to the
presence of small amounts of auxin, which are still present or
constantly formed again by the supply of auxin-precursor (or
-precursors) from the seed to the coleoptile (Skoog, 1937). This

conversion of precursor into auxin seems to be very sensitive
to slight alterations in the external conditions which even in
rooms with constant moisture and temperature cannot be al-
together avoided.

On account of this it may be preferred in future to make all
determinations of the auxin content with Auena-coleoptiles, of
which the seeds after the method of Skoog (1937) have been
removed 18 hours ahead. These coleoptiles after decapitation
are practically free from auxin and since no new precursor
can be supplied, all the curvatures found at a certain amount
of auxin will be equal. It also appears from the investigations
of Koningsberger and Verkaaik (1938), that the variability in
deseeded test plants is practically nothing.

First of all we examined, whether it was possible to inhibit
markedly the development of the lateral buds of decapitated
seedlings of Lupinus alhus by the application of hetero-auxin
solutions via the decapitated stem.

80 4 weeks-old seedlings of Lupinus alhus with an average of
8 expanded leaves were decapitated 20 mm above the first leaf
from below, the second leaf being inserted about 2 or 3 mm

TABLE I. Development of the buds in the axils of leaf 1 and leaf 2 of
seedlings of Lupinus albus decapitated above leaf 2 (experiment 1, 14/9/3S
-28/9/36).

') This experiment has been partly published already in a previous paper
(Ferman, 1938).

above the first leaf. The plants were divided into 5 series of
16 plants each. In 4 series an aqueous solution of hetero-auxin
in concentrations of respectively 5 in 10quot;, 1 in 10quot;, 5 in 10' and
1 in 10', and in one series tap water was applied twice a day
to the plants via the decapitated stem. After 8 and after 14 days
the lengths of the developing buds in the first and in the second
leaf axil were measured. As appears from table I and figure 1,
the development of the axillary buds was promoted weakly by
application of hetero-auxin 1 in 10' and 5 in 10', but it was
inhibited weakly (for about 20 per cent) by application of hetero-
auxin 1 in 10quot;, and the inhibition was very strong, though not
complete, by application of hetero-auxin 5 in 10quot; (respectivelyquot;
70 per cent after 8, and 50 per cent after 14 days), all series
compared with the blank tap water series.

It is obvious that the bud in the
axil of the second leaf generally
develops faster, than that in the
axil of the first leaf, though the
mean distance between the inser-
tion of both leaves is only very
small. Besides, this phenomenon
occurs in the series where the
growth of the axillary buds is in-
hibited as well as in the series
where it is promoted. Arranging
the buds per plant according to
the rate of their development, the
increase of the slower developing
bud in the first 8 days as well
as in the following 6 days proves
to be smaller than that of the
faster developing bud (see table II
and figure 2).

Already DosTaL (1926) and later
more particularly Snow (1931a)
have drawn attention to this phe-
nomenon. Both investigators believe
that a correlation between the two
lateral shoots exists similar to
that between terminal and lateral
jjhoots in the intact plant. The ex-
periments of chapter V (p. 226)

TABLE IL Development of the axillary buds of the first two leaves of
seedlings of Luvinus albus decapitated above the second leaf (experiment
1, 14/9/36—28/9736).

will clearly show that the same phenomenon — inhibition of the
growth of one lateral shoot by the other — occurs in Lupinus
alhus.

In some plants the axillary buds of the cotyledons also deve-
loped. As appears from table III, however, this development was
so irregular, that no conclusion can be drawn. Only it is striking,
that in the series, where the development of the axillary buds
of the first leaf-pair was most strongly inhibited (the series with
hetero-auxin 5 in 10quot;) also the axillary buds of the cotyledons
did not show the least development.

TABLE III. Development of the axillary buds of the cotyledons of seed-
lings of Lupinus albus decapitated above the second leaf (experiment 1,
14/9/36—28/9/36).

Simultaneously with the length of the axillary buds that of
the epicotyl from the cotyledons to the first leaf was also mea-
sured. In none of the series, however, any increase in length of
the epicotyl was observed, neither any swelling or thickening
of the stem did occur.

30 seedlings of Lupinus albus with an average of 5 expanded
leaves were decapitated 15 mm above the first leaf from below.
The plants were divided into 3 series of 10 plants each. In two
series an aqueous solution of hetero-auxin in concentrations of
respectively 1 in 10'' and 1 in 10quot;, and in one series tap water
was applied to the plants via the decapitated stem once a day.
After 15 days the lengths of the developing buds in the axils of
the first and the second leaf were measured. As appears from
table IV and figure 3, the development of the axillary buds was
not inhibited by application of hetero-auxin 1 in 10^, but very

strongly by hetero-auxin 1 in 10quot;, both compared with the blank
tap water series.

TABLE IV Development of the buds in the axils of leaf 1 and leaf 2
of seedlings of Lupinus albus decapitated above leaf 2 (experiment 2,

These results are similar to those of experiment 1. It is true
that the development of the axillary buds in that experiment in
all the series, is relatively much stronger than in this one, but
this probably is due to different conditions. The plants of experi-
ment 1, grown outside under glass during August and September,
showed an abundant growth, those of experiment 2, on the other

hand, grew in the greenhouse during January and February,
with an extra neon-radiation at night, but still under much more
unfavourable conditions; they showed a less vigorous growth.

The application of the fluids 15 days after the beginning of
the experiment having ended, the lengths of the axillary shoots
were measured once more 12 days later. As appears from table IV
and figure 3, the increase in length during these 12 days in the
two series with the application of hetero-auxin was slighter than
in the blank tap water series. So we find still an after-effect of

TABLE V. Development of the axillary buds of the first two leaves of
seedlings of Lupinus alhus decapitated above the second leaf (experiment

the hetero-auxin supply during the prece-
ding 15 days. The same is foimd in the
series with hetero-auxin 1 in 10', in which
the development of the axillary buds during
the first 15 days equaled that of the series
with water supply.

A faster development of the buds in the
axil of leaf 2 than those of leaf 1, is only
found in the series with tap water supply;
in the two series with a hetero-auxin ap-
plication the development of the buds in
the axil of leaf 1 is similar to that of leaf 2.
If, however, as was done in the preceding
experiment, we arrange the buds of each

Figure 4. Development of the axillary buds of
the first two leaves of seedlings of Lupinus albus
decapitated above the second leaf at application,
once a day, of hetero-auxin 1 in lOquot;, 1 in 10'
and tap water via the main stem; BBI slower bud,
llllllllll faster bud (experiment 2, 4/2/37—3/3/37).

plant according to the rate of their development, we find here
too that the increase in length of the slowly developing bud,
during the first 15 days as well as in the following 12 days, is
slighter than that of the faster developing bud (table V and
figure 4).

In the two previous experiments the plants were decapitated
just above the first leaf pair and we succeeded in inhibiting the
growth of the axillary buds by applying hetero-auxin solutions.
In the following experiment the plants were decapitated just
above the second leaf pair and we tried to find out how the
development of the axillary buds would be when applying hetero-
auxin.

20 seedlings of Lupinus albus with an average of 6 expanded
leaves were decapitated 10 mm above leaf 3. The plants were
divided into 2 series of 10 plants each. In one series an aqueous
solution of hetero-auxin in a concentration of 1 in 10quot; and in one
series tap water was applied to the plants via the decapitated
main stem once a day. After 15, 21 and 31 days the lengths of
the developing buds in the axils of the cotyledons and of the
first four leaves were measured.

As appears from table VI, it were chiefly the axillary buds
of the lower pair of leaves which expanded in both series. Only
in a few plants (their number is indicated in brackets) the

TABLE VL Development of the buds in the axils of the cotyledons and
of the first four leaves of seedlings of Lupinus albus decapitated above
the fourth leaf (experiment 3, 15/2/37—18/3/37).__

I Ö

'■I

r-l -S
tj

IJl

•T3

1 ^

gt;i w

1) between brackets the number of plants with developing cotyledonary
buds or axillary buds of leaf 3 and 4.

axillary buds of the cotyledons and of the
second leaf pair developed (only in one case
the axillary bud of leaf 4). As to the develop-
ment of the axillary buds of the first pair of
leaves, we find a smaller increase of length
when applying hetero-auxin 1 in 10°, than
when tap water is applied (see also figure 5).
During the first 15 days the inhibition was
about 30 per cent, during the following 16
days 10 per cent. This difference is smaller
than that in the two preceding experiments,
probably as the place of application was far-
ther removed.

In the series with the application of hetero-
auxin 1 in 10® the development of the buds
in the axil of leaf 1 as an average is the
same as that of the buds of leaf 2; in the
series with tap water supply the development

Figure 6. Development of the axillary buds of the
first two leaves of seedlings of Lupinus albus decapi-
tated above the fourth leaf at application, once a
day, of heterc-auxin 1 in 10® and tap water via the
main stem; H slower bud,llllllllll faster bud (experiment
3, 15/2/37—18/3/37).

of the axillary buds of leaf 2, however, is as an average much
stronger than that of the buds of leaf 1. Here too an arrangement
of the buds as to the rate of their development shows, that the
buds which develop faster in the beginning, remain ahead as
compared to their slower partners (see table VII and figure 6).

TABLE Vn. Development of the axillary buds of the first two leaves of
seedlings of Lupinus alhus decapitated above the fourth leaf (experiment 3,
15/2/37—18/3/37).

The inhibition of the development of the axillary buds by the
application of hetero-auxin solutions via the decapitated main
stem, was weaker in the experiments 2 and 3, with an application
once a day, than in experiment 1 with a twice-a-day application.

TABLE Vin. Development of the buds in the axils of leaf 1 and leaf 2
of seedlings of Lupinus alhus decapitated above leaf 2 (experiment 4,
23/2/37—22/3/37).

For this reason another experiment was made with an application
twice a day of hetero-auxin solutions of various concentrations.

40 seedlmgs of Lupinus albus with an average of 6 expanded
leaves were decapitated 15 mm above the first leaf from below.
The plants were divided into 4 series of 10 plants each. In 3
series an aqueous solution of hetero-auxin in a concentration

of respectively 1 in 10®, 1 in 10»
and 1 in 10', and in one series
tap water was applied to the
plants via the decapitated stem
twice a day. After 13, 16, 20, 23
and 27 days the lengths of the
developing buds in the axils of

the first and of the second leaf
were measured. As appears from
table VIII and figure 7 the deve-
lopment of the axillary buds was

Figure 8. Development of the axil-
lary buds of the fh:st two leaves of
seedlings of Lupinus albus decapita-
ted above the second leaf at appli-
cation twice a day of hetero-auxin
1 in 105, 1 in lO«, 1 in 10' and tap
water via the main stem; Mi slower
bud, llllllllll faster bud (experiment 4,
23/2/37—22/3/37).

inhibited weakly by hetero-auxin 1 in 10' and 1 in 10quot;, but very
strongly by hetero-auxin 1 in lO'^, at least during the first 20
days. During the last 7 days the axillary buds of the series with
a hetero-auxin 1 in lO'-'-application showed a remarkably rapid
development. The more remarkable since the two other series
with hetero-auxin supply particularly during these last 7 days
still showed a decidedly smaller increase in length of the axillary
buds than the series with tap water. We are wondering, whether
some error has been made here, for instance an application of
tap water instead of hetero-auxin 1 in 10\ In the test protocols,
however, no indication can be found for such a mistake so that
these results must be given here unchanged.

On an average the development of bud 2 is not much faster
than that of bud 1, except in the series with hetero-auxin 1 in
10°, where bud 2 shows a decidedly stronger development. When
arranging the buds according to the rate of their development,
we find, however, again a constantly stronger increase in length
of the buds, which developed more rapidly at the beginning (see
table IX and figure 8).

TABLE IX. Development of the buds in the axils of the first two leaves
of seedlings of Lupinus albus decapitated above the second leaf (experi-
ment 4, 23/2/37—22/3/37).

In the middle of February pieces of 2 years-old twigs of a
shrub of Ligustrum vulgare were cut off at a length of 45 mm.

They were cut in such a way, that each piece had about the
same thickness, and contained at 15 mm from the top two opposite,
still dormant buds, 1 to 2 mm long. 40 of these cuttings were
divided over 4 series of 10 each and planted in an earthen box
with damp mould, which w^as put in the greenhouse. Once a day
an aqueous hetero-auxin solution of a concentration of respecti-
vely 1 in 10® and 1 in 10' was applied to two series via the
apical cut surface and to one series tap water was applied, whilst
to the fourth series no fluid was supplied at all. The fluids were
absorbed more slowly than in the preceding experiments with
seedlings of Lupinus alhus. After 8, 12 and 18 days the lengths
of the developing buds were measured. As appears from table X
and figure 9 the development of the buds was slightly promoted
by the application of hetero-auxin 1 in 10' and inhibited to a
slight degree by the application of hetero-auxin 1 in 10«, in
comparison with the development when tap water was applied.
The development of the buds in the series without any application
of fluid, was even much smaller, however, so that we must
conclude that the mere application of water already promotes
the developing of the buds.

TABLE X. Development of the lateral buds of single-node cuttings of
Ligustrum vulgare (experiment 5, 12/2/37—2/3/37).

In none of the series anything could be observed of root for-
mation in the cuttings during the experiment.

twigs the place of their insertion cannot be responsible for the
difference in rate of development. When arranging the buds
according the rate of developing, however, we find the same
as we did in the experiments with seedlings of Lupinus alhus:
the buds, developing faster in the beginning, keep on increasing
their advance more and more. This phenomenon is even more
striking in the Ligustrum-cuttings than in Lupinus-seedlings,
for the ratio slower: faster bud is here even more unfavourable
for the slower bud (see table X).

When we examine the results of the preceding experiments,
it appears very clearly, that it is possible to inhibit the growth
of axillary buds of decapitated seedlings of Lupinus alhus by
an application, via the cut surface of the stem, of aqueous
hetero-auxin solutions of a sufficient concentration. The experi-
ment with cuttings of Ligustrum vulgare is less convincing, but
points in the same direction. It appears at the same time that
hetero-auxin concentrations lower than 1 in 10« have no inhi-
biting but rather a promoting effect on the development of the
axillary buds. On the whole, we find a strong inhibition oidy
when hetero-auxin solutions of a concentration 5 in 10quot; and
1 in lO'' are applied. These concentrations are of about the same
order of magnitude as the auxin concentration, which may be
expected to be present in intact plants. It may be possible that
still higher concentrations might cause a stronger inhibition;
it did not seem important to us to find that out, since little value
can be attached to the results obtained with so unphysiologically
high concentrations.

lt;1933, 1934) who clearly showed, that the termmal bud has an
inhibiting influence on the development of the lower lateral
buds and that after decapitation auxin, applied via the deca-
pitated main stem, has a similar inhibiting effect. However, the
character of the action of auxin in this correlative inhibition
still remains in the dark. Whether a direct action of auxin as
a consequence of its high concentration is in the play, has to
be discriminated by determination of the auxin content (see
chapter VII and VIII, p. 238 and 242).

As the exact measuring of lengths in experiment 1 did not
.give any indication for growth in the main stem and as swel-
lings could not be observed anywhere either — as a matter of
fact, we do never find the latter in intact plants —, the idea
of Laibach (1933) that growing processes in the stem themselves
have an inhibiting influence on the axillary buds, seems rather
improbable.

Besides, several facts must to be accounted for which hardly
fit in the existing theories. For instance: notwithstanding the
slight difference in place (on the average only 2 tot 3 mm), bud
2 nearly always developed faster than bud 1. It is true, that in
some series no difference was found between the average lengths
of the two buds, but in none of the series bud 1 developed faster
than bud 2. Further it is remarkable that in experiment 3,
where the plants were decapitated a little above the second
pair of leaves, the development of the axillary buds of the second
pair of leaves was so slight, as well at application of hetero-
auxin as at application of tap water. These facts require a
further explanation.

The fact, that of two developing axillary buds of a plant, one
generally develops faster than the other must be considered
too as a correlative inhibition of one lateral shoot by the other;
it will be examined more closely in chapter V (p. 226).

In addition to the application of aqueous hetero-auxin solutions
we also tried to inhibit the development of the lateral buds by
applying lanolin hetero-auxin pastes. The advantage of these
pastes is, that they can be applied everywhere on the plant and
thus also in the immediate surroundings of that part of the
plant of which we try to affect the growth. In the application

of aqueous hetero-auxin solutions some tissue of the stem always
was included too. A disadvantage of the paste method is, how-
ever, that we can never be sure how much hetero-auxin is
absorbed by the plant from the paste and neither, whether in
the application of hetero-auxin pastes of various concentrations,
the quantities absorbed are proportional to these concentrations.

40 seedlings of Lupinus alhus with an average of 5 expanded
leaves were divided into 4 series of 10 plants each. In two
series the plants were decapitated 15 mm above leaf 1 and in
two other series as closely as possible above leaf 2. The distance
between leaf 1 and leaf 2 was 3 mm on an average. In each set
of 2 series the cut surface of the stem of one of the series was
supplied with an amount of lanolin hetero-auxin paste 1 in 10quot;,
whilst in the other two series this was done with lanolin paste
without hetero-auxin. The pastes were renewed daily. After 15
days the lengths of the developing buds of the first leaf-pair
were measured. As appears from table XI and figure 10, in the
series with the application 15 mm above leaf 1 as well as in the
series with the application just above leaf 2, the development
of the axillary buds was inhibited by the application of lanolin
hetero-auxin paste 1 in 10quot; for about 50 per cent, as compared

TABLE XI. Development of the buds in the axils of leaf 1 and leaf 2
of seedlings of Lupinus albus decapitated above leaf 2 (experiment 6,
4/2/37—3/3/37).

to their development in the corresponding series with an ap-
plication of blank lanolin paste. If we compare both series with
the paste just above leaf 2, with the corresponding series with
the paste 15 mm above leaf 1, we see that in the former series
the development of the lateral buds is about 30 per cent smaller
than in the corresponding of the latter. Since also in the ap-
plication of blank lanolin paste just above leaf 2, the develop-
ment was smaller thari with the blank paste 15 mm above leaf 1,
we can only conclude, that the decapitation and the application
of paste just above the axillary buds has a detrimental influence
on their development. This also appears from the fact, that in

the series where the paste was
applied just above leaf 2 the deve-
lopment of the bud in the axil of
this leaf was slighter than that of
the bud in the axil of leaf 1. This
phenomenon was not found in any
of the other experiments.

After the 15th day the applica-
tion of paste was stopped. 12 days
afterwards the lengths of the axil-
lary buds were measured once more
and it appeared (see table XI)
that the increase in length was
about the same in all the series.
So here we do not find an after-
effect of the hetero-auxin applica-
tion, as we did in experiment 2

p/ain lanolin paste
15 mm above

'Smmaoo^e
r^ teafl jus! above

after 15 days

Figure 11. Development of the
axillary buds of the first two
leaves of seedlings of Lupinus
albus decapitated above the se-
cond leaf at application onto
the cut stirface of the main
stem of lanolin hetero-auxin
paste 1 in 10« and plain lanolin
paste, 15 mm above leaf 1 and
just above leaf 2; KI slower
bud, illlllllll faster bud (experiment
6, 4/2/37—3/3/37).

TABLE XIL Development of the axiUary buds of the fu:st two leaves
of seedlings of Lupinus albus decapitated above the second leaf (experi-
ment 6, 4/2/37—3/3/37).

If arranging the buds according the rate of their development,
we also get the same relations here between more slowly and
faster developmg buds as we did in the experiments of the
preceding chapter (see table XII and figure 11).

20 seedlings of Lupinus albus with an average of 6 expanded
leaves were decapitated 10 nun above leaf 1. The plants were
divided into two series of 10 plants each. A ring of lanolin paste
was put around the stem at the insertion of the first leaf-pair,
in one series containing hetero-auxin at a concentration of 1 in
10^ in the other one only tap water. The pastes were renewed
every 3 days. After 13, 19, 26, 30 and 34 days the lengths of the
developing buds were measured. As appears from table XHI'
and figure 12, the development of the axillary buds in the series
with the application of hetero-auxin paste 1 in 10quot; was smaller
than in the series with plain lanolin paste.

If we examine the increase in length in the successive periods
(see table XIV), it appears, that this increase durmg the first
19 days in the series with hetero-auxin 1 in 10quot; was about 35
per cent smaller than in the control series; during the next
7 days the difference in increase is only about 20 per cent, whilst
during the last 8 days the axillary shoots of the series with
hetero-auxin increased in length more than 20 per cent faster
than the control series. During these last 8 days the hetero-auxin

TABLE Xm. Development of the axillary buds of the first two leaves
of seedlings of Lupinus albus decapitated above the second leaf (experi-
ment 7, 17/2/37—23/3/37).

has no longer an inhibiting effect. That in the whole the bud
inhibition in this experiment was weaker than in the preceding
one, may be caused by the fact that in this experiment the pastes
were renewed every 3 days, whilst in the preceding experiment
this was done every day. In both series of this experiment the
development of bud 2 was on an average stronger than that
of bud 1. By arranging the buds according to the rate of then-
development, we obtained results which equaled those of the
preceding experiments too. It seems superfluous therefore to
mention them again for this experiment in a separate table and
figure.

TABLE XIV. Development of the axillary buds of the first two (leaves
of seedlings of Lupinus alhus decapitated above the second leaf (experi-
ment 7, 17/2/37—23/3/37).__

Also some experiments with an application of lanolin hetero-
auxin paste were made with cuttings of Ligustrum vulgare.

In the middle of February the stems of 2 years-old twigs
from a shrub of Ligustrum vulgare were cut into 20 pieces all
as equal as possible. These pieces were 45 mm long and con-
tained one dormant bud, about 5 mm long, at 15 mm distance
from the lower side; the opposed bud was removed. Then these
single-node cuttings were split into two equal halves from the
base to a little over the node. Into this split some lanolin paste
was applied on the level of the dormant bud. In one series of
10 cuttings this paste contained hetero-auxin in a concentration
1 in 10quot;, in the other séries of 10 cuttings only tap water. The
cuttings were planted in an earthen pot with leaf mould which
was placed in the greenhouse. Every 2 days the pastes were
renewed. After 7 and after 14 days the lengths of the developing
buds were measured. The average length of the series with the
application of lanolin hetero-auxin paste 1 in 10quot; was respectively
13 and 28 mm, for the series with the application of plain
lanolin paste it was 14 and 28 mm. We see, from this that
between the two series not the least difference in the develop-
ment of the lateral bud could be observed.

On account of the negative results of the preceding experiment
a new experiment was made with hetero-auxin paste of a higher
concentration and in a somewhat different way of application.
For this purpose 30 single-node cuttings of Ligustrum vulgare
were used, each with a length of 30 mm and with an equal

thickness of stem. The upper part of these cuttings was cut off
obliquely in such a fashion that from the two opposing buds at
the apex of the cutting one was removed. The remaiaing bud
had a length of 1 tot 2 mm. The pieces were divided into 3
series of 10 and in all the series lanolin paste was applied to
the oblique cut surface at the apex, in two series with hetero-
auxin in a concentration of respectively 1 in 10' and 1 in 10®
and in one series without hetero-auxin. The cuttings were
planted in an earthen pot with mould and placed in the green-
house. The pastes were renewed very 2 days. After 6, 9, 13
and 15 days the length of the remaining bud was measured. As
appears from table XV, there is some difference between the
development with the hetero-auxin pastes and the plain lanolin
paste. The difference, however, is so slight, that we need not
attach much value to it.

TABLE XV. Development of the lateral bud of smgle-node cuttings of
Ligustrum vulgare (experiment 9, 9/3/37—24/3/37).

It clearly appears from the results with lanolin hetero-auxin
paste 1 in 10quot; to decapitated seedlings of Lupinus alhus that
also by this method of auxin application the growth of lateral
buds can be inhibited. The inhibition in the application of a
hetero-auxin paste 1 in 10quot; in the immediate surroundings of
the axillary buds, was as strong as in the application 12 mm
higher up on the stem. According to the theory of Laibach (1933)
the auxin would first bring about growth processes and cell
divisions in the stem and by these secondarily an inhibiting
influence would be exerted on the growth of the axillary buds.
Between the place of auxin application or production and the
axillary buds in question, some tissue must necessarily be
present, capable of this growth. In our experiment with the
application of hetero-auxin paste quite close to the axillary
buds no growing interiacent tissue is present, but still we find
an inhibition not slighter than in the hetero-auxin application

12 mm higher on the stem. From this it appears that Laibach's
theory hardly can be right.

In the cuttings of Ligustrum vulgare the application of lanolin
hetero-auxin paste 1 in 10quot; as near as possible to the still dor-
mant lateral buds did not cause any inhibition of their develop-
ment, whilst in experiment 5, taken at about the same time,
an application of aqueous hetero-auxin solutions indeed had
some effect. The reason probably is, that the hetero-auxin is
absorbed from the lanolin paste by these woody cuttings only
to a slight degree, whilst in the applications of the aqueous
solutions the hetero-auxin together with the fluid is much more
easily absorbed by the plant. Also on account of these results,
we are of opinion, that wherever it is possible, the application
of auxin in the form of aqueous solutions, is to be preferred to
its application as lanolin pastes.

The experiments, treated in both preceding chapters, showed
the possibility of inhibiting the growth of lateral buds in deca-
pitated seedlings of Lupinus albus by applying aqueous hetero-
auxin solutions or lanolin hetero-auxin pastes to the cut surface
of the stem. This made it highly probable, in view of the analogic
behaviour of hetero-auxin and auxin-a (see chapter II, § 2,
p. 203), that in the correlative inhibition of lateral buds by the
terminal shoot auxin acts as a correlation carrier. However,
the exact role of auxin in this correlation, still remains in the
dark. At the same time our attention was drawn to a pheno-
menon which also could be considered as correlative inhibition,
namely the fact, that in the case of two developing axillary
buds inserted on the same level of the decapitated stem, one
of the buds generally develops more rapidly than the other.
It seemed important to find out, first whether actually inhibition
of the growth of one lateral shoot by the other occurs and
secondly, whether auxin is the correlation carrier here too.

1) This experiment has already been published in a previous paper
(Ferman, 1938).

above the first pair of leaves and of which the two axillary
buds of leaf 1 and leaf 2 had developed, so called quot;two-shoot
plantsquot;, 30 plants were selected, of which the two lateral shoots
were distinctly unequal in length. The plants were divided into
3 series of mutually comparable plants. Of all the plants the
longer lateral shbot was cut off at 10 mm above its base. To
two of the series an aqueous hetero-auxin solution of a concen-
tration of resp. 1 in 10® and 1 in 10® was applied twice a day
via the decapitated longer lateral shoot and to one series tap
water. Every 3 or 4 days the length of the remaining shorter
shoot was measured from its base to the apical bud. From the
results summarized in table XVI and figure 13, it appears, that
during the test period of 18 days, the shorter lateral shoot
showed rather a good growth when tap water was applied via
the decapitated lateral shoot; when applying hetero-auxin 1 in
10® its growth was slightly less (about 10 per cent), whilst in

TABLE XVI. Growth of the shorter lateral shoot of „two-shoot plantsquot;
of Lupinus alhus (experiment 10, 4/3/37—22/3/37).

the apphcation of hetero-auxin 1 in 10' the growth of the shorter
lateral shoot was strongly inhibited (for about 75 per cent), as
compared with the growth when tap water was applied.

Some corresponding experiments with two-shoot plants of
Lupinus albus (the experiments 27—30) will be treated in chapter
IX, § 2, p. 258). The results of these experiments, however, all
point in the same direction. Thus in experiment 27 with a test-
duration of 6 days we find an inhibition of about 70 per cent
of the growth of the shorter lateral shoot, when applying hetero-
auxin 1 in 10' via the decapitated longer lateral shoot, com-
pared with the growth of the shorter lateral shoot of plants of
which the longer one had been decapitated, without any fluid
being applied. In experiment 28 the increase in length of the
shorter lateral shoot after 14 days, when applying hetero-auxin
1 in lOquot;', is about 50 per cent of that of plants to which tap water
was applied. At the same time in a set of intact two-shoot plants
the length increase of the shorter lateral shoot was about 65
per cent of that of the longer lateral shoot.

In experiment 29 the length increase of the shorter lateral
shoot at an application of hetero-auxin 1 in lOquot;' is inhibited in
one series after 7 days for about 30 per cent, in another series
after 14 days for about 75 per cent, compared with the growth
of the shorter lateral shoot of corresponding series with an
application of tap water via the decapitated longer lateral shoot.
Finally we find in experiment 30 that, when applying hetero-
auxin 1 in lOquot;^ via the decapitated shorter lateral shoot the
growth of the longer lateral shoot in one series is inhibited after
7 days for about 10 per cent, in another series after 15 days
for about 40 per cent, compared with the growth of the longer
lateral shoot of corresponding series with an application of tap
water.

The experiments mentioned above showed the possibility of
inhibiting the growth of the shorter, or of the longer, lateral
shoot in two-shoot plants of Lupinus albus by applying an
aqueous hetero-auxin solution 1 in 10'' via the decapitated
second (resp. longer, or shorter) lateral shoot, compared with
the growth of these lateral shoots when applying tap water or
no liquid at all. This makes it very probable that in the intact
two-shoot plant too, the growth of the shorter lateral shoot is
inhibited by the longer one and that also in this case of corre-
lative inhibition auxin is the correlation carrier. The correlative

inhibition of axillary buds by the terminal shoot and the cor-
relative inhibition of the one lateral shoot by the other, should
therefore be considered as phenomena of an analogous character.
This is of importance in our later efforts to find an explanation
for these phenomena.

Inhibition of young shoots and lateral buds by application of
;nbsp;hetero-auxin solutions from below.

From the experiments of Le Fanu (1936) and Snow (1936) it
appeared that the growth of the young shoots and the axillary
buds of decapitated shoots of Pisum sativum can be inhibited
by hetero-auxin when applied to them from below. This pheno-
menon may be linked to that of the correlative inhibition of
lateral buds and shoots, so that it seemed important to make
the same experiments with seedlings of Lu-pinus alhus too.

40 two weeks-old seedlings of Lupinus albus with as an average
1 expanded leaf were cut off 40 mm below the cotyledons. They
were divided over 4 series of 12 shoots. Each shoot was put
separately in a glass tube 10 cm long and with a diameter of
15 mm. The tubes in 3 series were filled with 14 cm' of an
aqueous hetero-auxin solution of a concentration of resp. 1 in
10', 4 in 10« and 1 in lO'' and in one series with tap water. The

TABLE XVn. Growth of shoots of seedlings of Lupinus albus cut off
40 mm below the cotyledons (experiment 11, 7/10/36—16/10/36),

Figure 14. Growth of shoots of seedlings of Lupinus albus cut off 40 nun
below the cotyledons and placed with their basal ends in glass tubes with
hetero-auxin 1 in 10^, 4 in 10«, 1 in 10« and tap water (experiment 11,
7/10/36—16/10/36).

shoots rested with their cotyledons on the edge of the glass
tubes and their hypocotyl was immersed in the liquid for about
2 cm. Every 2 or 3 days the hetero-auxin solutions were renewed.
At the beginning of the experiment and after 3, 6 and 9 days
the shoots were measured, that is a) the length of internode 1
(from the cotyledons to leaf 1), b) the greatest measurable
length from the cotyledons to the end of a leaf and c) the
number of expanded leaves. It appears from table XVII and
figure 14 that the hetero-auxin solutions 4 in 10« and 1 in 10«
had no influence on the development of the shoots, as compared
with their growth in tap water. The hetero-auxin solution 1 in
10'quot;', on the other hand, produced a strong inhibition.

The development of these shoots by hetero-auxin 1 in lOquot;' is
influenced very unfavourably, as appeared also from the fact,
that the petioles of these shoots showed a distinct epinastic
curvature 3 days after the beginning of the experunent. Further
the leaflets were somewhat folded inward alongside their
midrib. After 9 days all the cotyledons in this series showed
a brownish-yellow discoloration and in half of the cases they had
already dropped off.

24 seedlmgs of Lupinus alhus with on an average 2 expanded
leaves were cut off 30 mm below the cotyls. The shoots were
divided over 2 series of 12 plants each and placed separately
in glass tubes in the same way as in the previous experiment.
These tubes were filled in one series with an aequeous hetero-
auxin solution 1 in 10quot; and in the other with tap water. These
liquids were renewed every 3 days. The hypocotyl of these
shoots was immersed in the liquid for about 1 cm. At the be-
ginning of the experiment and after 3, 6, 8, 12 and 17 days the
lengths of the shoots were measured, that is the length of inter-
node 1 (from the cotyledons to leaf 1) and the greatest measur-
able length from the cotyledons to the end of a leaf. From table
XVIII and figure 15 it appears, that by placing the shoots in

Figure 15. Growth of shoots of seedhngs of Lupinus albus cut off 30 mm
Ijelow the cotyledons and placed with their basal ends in glass tubes with
hetero-auxin 1 in 10® and tap water (experiment 12, 8/1/37—25/1/37).

TABLE XVIII. Growth of shoots of seedlmgs of Lupinus albus cut off
30 mm below the cotyledons (experiment 12, 8/1/37—25/1/37).

the 1 in 10» hetero-auxin solution the growth is slightly inhi-
bited, in comparison with their growth in tap water. T^is
inhibition is not strong and actually only occurs during the first
3 days of the experiment, the increase of length of the shoots
in the hetero-auxin 1 in 10» then being about 40 per cent less
than of the shoots in tap water. Afterwards the development
of the shoots in both series runs about parallel. After the 8th
day the growth is only very slight. The two curves in figure
15 than begin to look like BLACKMAN-Curves and so we must
accept, that between the 6th and the 8th day one or more
factors begin to act as limiting factors for the growth.

In this experiment which runs almost parallel with the pre-
cedmg one, 36 seedlings of Lupinus alhus with on an average
2 expanded leaves were cut off 30 mm below the cotyledons.
The shoots were divided over 2 series, one of 24 and one of 12
plants, and placed again separately as in the previous experi-
ment in glass tubes. In the series of 24 these tubes were filled
with a hetero-auxin solution 1 in 10' and in the other series
with tap water. Every 3 days the liquids were renewed. In the
beginning of the experiment and after 3, 5, 11 and 16 days the
shoots were measured, that is the length of internode 1 and the
greatest measurable length beginning at the cotyledons. From
table XIX and figure 16 it appears, that the growth of the shoots
in the hetero-auxin solution 1 in 10' was about the same as the
growth in tap water.

In order to make the results of this experiment and those of
the preceding one more visually comparable, the joined results
of these two experiments were plotted in figure 16. This was
done by shifting the curves of the hetero-auxin series in both

TABLE XIX. Growth of shoots of seedlings of Lupinus albus cut off
30 mm below the cotyledons (experiment 13, 9/1/37—25/1/37).

Figure 16. Growth of shoots of seedlings of Lupinus albus cut off 30 mm
below the cotyledons, and placed with their basal ends in glass tubes with
hetero-auxin 1 in 10', 1 in 10« and tap water (experiment 12 and 13,
8/1/37—25/1/37).

experiments to such an extent that their initial point coincides with
that of the series in tap water. As appears from the figure,
there is a good conformity between the two series in tap water,
while we find a slight inhibition for the series in hetero-auxin
1 in 10' and a somewhat stronger inhibition for the series in
hetero-auxin 1 in 10«.

An analogous experiment was made with shoots of Pisum
sativum, variety quot;Kaapse groenequot;. 24 two weeks-old seedlings
with 2 to 3 expanded leaves were used; 16 of the seedlings

were cut off at 40 mm below leaf 3, and these shoots, like the
shoots of Lupinus albus in the preceding experiment, were
placed separately in glass tubes. In one series of 8 shoots the
tubes were filled with a hetero-auxin solution 4 in 10« and in
another series of 8 with tap water. The shoots rested with their
3rd leaf on the edge of the glass tubes and thus their bases
were immersed in the liquid for about 2 cm. Every 2 or 3 days
the liquids were renewed. The remaining 8 plants were left
intact in the same place where they had also been grown,
namely in mould in the greenhouse; only their first two scales

Figure 17 Growth of shoots of seedUngs of Pisum sativum cut off 40 mm
below leaf 3 and placed with their basal ends in glass tubes with hetero-
auxm 4 in 10« and tap water and of shoots of intact plants (experiment 14.
21/9/36—7/10/36).

TABLE XX. Growth of shoots of seedhngs of Pisum sativum (experiment
14, 21/9/36—7/10/36).

beginning of the experiment and after 3, 5 and 10 days the
lengths of the internodes above leaf 3; internode 4 (from leaf
3 to leaf 4), 5 (from leaf 4 to leaf 5), etc. were measured. As
appears from table XX and figure 17 the growth of the shoots,
when placed in hetero-auxin 4 in 10quot; was the same as when
placed in tap water; the growth of the intact plants, however,
was much stronger.

It seemed important to investigate whether by placing young,
decapitated shoots of Lupinus albus in hetero-auxin solutions of
various concentrations, the growth of the developing buds would
be inhibited too. In the following experiment we also tried to
find out how much the auxin content of these shoots increased
by placing them in these hetero-auxin solutions.

From 90 four weeks-old seedlings of Lupinus albus with on
an average 3 expanded leaves, internode 1 having an average
length of 76 mm (from cotyledons to leaf 1), 60 were cut off
30 mm below the cotyledons and decapitated just above leaf 2.
The cut-off shoots, 10 together, were put into small glass trays.
These trays were covered with paraffined card-board lids, in
which 10 holes had been punched, through which the hypo-
cotyls of the shoots could be put. The glass trays were filled
with 250 cm'' liquid, two with an aqueous hetero-auxin solution
of concentration 1 in 10quot;', two with hetero-auxin 1 in 10quot; and
two with tap water. The shoots rested with their cotyledons
on the card board lids and their hypocotyl was immersed in
the liquid for about 1 cm. Every 3 days the liquids were renewed.
From the 30 remaining plants 20 were decapitated just above
leaf 2, but further left intact. Of the 10 remaining plants the

auxin content was determined of 10 mm of the stem at the
node of the first pair of leaves (the method has been described
in chapter II, § 3 and 4, p. 203 and 205).

7, 11 and 14 days after the beginning of the experiment, of
respectively 7, 7 and 6 shoots of each of the 4 series the auxin
content was determined of 10 mm of the stem at the node of
the first pair of leaves. The results of these determinations of
the auxin content, have been summarized in table XXI and
figure 18. Before determining the auxin content the lengths of
the axillary buds of each set of shoots were measured; the results
of these measurings too have been summarized in table XXI.
(leaves 1 and 2) with their axillary buds were removed. At the

TABLE XXI. Auxin content of 10 mm of the stem at the node of the
first leaf-pair of shoots of Lupinus albus decapitated just above the second
leaf, and development of the axillary buds of these shoots (experiment 15,
15/4/37—29/4/37).

7 ,
0	2	7
0	2	5
0	2	6
0	10	15

of intact, merely ii2 5»±l 0* I2,9'' l 3» - ** 14,7quot;±1,0'' 0
decapitated plants ! ' '

It is obvious from these results that the auxin content of the
stem at the level of the first pair of leaves of the shoots, placed
in hetero-auxin 1 in 10^, and 1 in 10«, is higher than of the shoots
placed in tap water. This shows that the hetero-auxin has been
absorbed by the shoots and transported upwards. Between the
shoots put in hetero-auxin 1 in lO'^ and in 1 in 10« there is no
difference, however, as regards the auxin content at the node of
the first leaf-pair. In the merely decapitated controls the auxin
content in the same place is somewhat lower than in the shoots
in hetero-auxin solutions, but it is considerably higher than in
the shoots in tap water. The development of the axillary buds
of these shoots, however, is strikingly uniform: between the
series in hetero-auxin and in tap water there is but little diffe-
rence. These series, however, distinctly remain behind the series
of decapitated plants, still standing in the soil. The shoots in
hetero-auxin 1 in lO'^ showed a toxic effect exerted on them by
this solution. One day after the beginning of the experiment the
petioles were already epinastically curved and the leaflets were
turned inward alongside their midrib. 6 days later the leaves
became yellowish green and wilted; 11 days after the experi-
ment had begun the leaves and cotyledons from part of the
shoots dropped off.

The experiments discussed in this chapter show the possibility
of inhibiting cut off shoots of Lupinus albus by placing them in
an aqueous hetero-auxin solution. This inhibition is not strong,
however, as compared with the growth in tap water and also
proved to be rather dependent on the age of the shoots, which
corresponds with the results of Snow (1936). In shoots of plants
with one expanded leaf a hetero-auxin solution 4 in 10« and
1 in 10quot; caused no inhibition, but a hetero-auxin solution 1 in 10quot;'
did. In another experiment with shoots with two expanded leaves
a hetero-auxin solution 1 in 10' already caused a very slight
inhibition of growth, this inhibition being somewhat stronger
in hetero-auxin 1 in 10«.

In the only experiment with Pisum sativum no inhibition of the
growth could be obtained by placing the shoots of plants with
4 to 5 expanded leaves in hetero-auxin solution 4 in 10quot;. Also
the development of the axillary buds of decapitated shoots of
Lupinus albus was not influenced by placing them in hetero-auxin
solutions 1 in 10quot; and 1 in 10', as compared with their growth
in tap water. It is, however, striking that the growth of the shoots

and the axillary buds in hetero-auxin and in tap water is always
less than that of shoots of control plants left in the soil. The
growth-curves of the cut-off shoots after some time all show
a type of BLACKMAN-curves. This means that after some time one
or more factors act as limiting factor.

From the determination of the auxin content of the decapitated
shoots in hetero-auxin 1 in 10», 1 in 10«, in tap water and of
plants still rooted in the soil, it appeared that the auxin content
of the shoots in tap water was distinctly less than that of plants
in the soil, whilst that of the shoots in the hetero-auxin solutions
was still higher. From this we may conclude: 1) the auxin
content decreases after the cutting off of the shoots and placing
them in tap water, 2) when placing the shoots in hetero-auxin
solution this hetero-auxin is absorbed by the shoots and trans-
ported (probably by the transpiration stream) in acropetal direc-
tion. At the same time, however, it was proved, that hetero-auxin
1 in 10' applied in this way had a toxic effect, noticeable in the
epinastic movement of the petioles, the folding of the leaflets,
the yellowish-green discoloration, and the dropping of cotyledons
and leaflets.

It was beyond the scope of my actual subject to investigate
systematically the auxin content of the growing plant. To enable
myself, however, to compare decapitated plants in which the
development of lateral buds and shoots had been artificially

inhibited by hetero-auxin with in-
tact plants, the auxin content of
the latter was determined too.

Of a set of 40 one week-old
seedlings of Lupinus alhus, of which
the cotyledons had not yet split,
the auxin content of 20 plants was
determined, i.e., of the cotyledons
, . and of two successive 15 mm long
sections of the hypocotyl exactly

length of the hypocotyl being about 65 mm. The crushing of the
cotyledons when extracting the auxin, was rather difficult. The
possibly imperfect extraction may be responsible for the low
auxin content found in the cotyledons. 4 days later in the
remaining 20 seedlings the cotyledons had split and the plumule
had grown out to a length of 35 mm, the hypocotyl having an
average length of 107 mm. The auxin content of these plants
was determined too, i.e., of the plumule, the cotyledons and two
successive pieces of 20 mm of the hypocotyl directly below the
cotyledons. The results of these determinations have been sum-
marized in figure 19.

The amount of auxin that could be extracted from the coty-
ledons appears to be equally low at both stages. After the splitting
of the cotyledons and the growing out of the plumule, however,
we find a distinct increase of the auxin content of the hypocotyl.
The plumule too proves to contain a fairly considerable amount
of auxin.

Besides very young seedlings of Lupinus alhus, the auxin
content was also determined of a number of seedlings, which
were already well developed.

Of 10 plants of a set of 20 5
weeks-old seedlings of Lupinus alhus
with on an average 8 expanded
leaves the auxin content was de-
termined in stem sections of 10 mm,
a) above the node of the 2nd leaf-
pair, b) at this node, c) below this
node, d) above the node of the 1st
leaf-pair, e) at this node and f)
below this node. Internode 2 in
these plants (from leaf 1 to leaf 3)
had an average length of 39 mm
and internode 3 (from leaf 3 to
leaf 5) of 28 mm.

5 days later the auxin content
was determined of the remaining
10 plants of the same stem sections
Figure 20. A^ content ofnbsp;besides also of a piece of

length of 37 mm and internode 3 of 45 nmi; the average number
of expanded leaves was 9.

From this figure we can see that the auxm content ot the
stem is rather high all over its length; there is little difference
in the auxin content of the stem at different points. In the first
set of 10 plants the auxin content was a little lower at the base
than near the top, in the second set of 10, 5 days later, the auxin
content was higher in the middle than above or below it. These
differences, however, in our opinion are too slight, to evaluate
them. This experiment clearly proves, that there is no essential
difference between the auxin content of the higher and of the
lower part of the stem.

For this experiment 20 8 weeks-old seedlings of Lupinus alhus
were taken with as an average 10 expanded leaves and 4 deve-
loped internodes. The plants were not in optnninn condition, the
leaves lower on the stem were already dropping off. The auxin
content of 10 of these plants was determined in stem sections
of 20 mm, a) and b) two successive pieces just below the terminal
bud, c) a piece half-way between b) and d), d) a piece just

above leaf 2 and e) a piece just
below it. From the cotyledons to
the terminal bud these plants had
an average length of 172 mm.
7 days later the auxin content
ynbsp;was determined of the same stem

sections of the 10 remaining plants.
These plants then on an average
2.?»«- rnbsp;had 13 expanded leaves and their

Probably in consequence of the
less favourable conditions of the
plants, the auxin content of the
stem is lower than that in the
preceding experiment. In the second
series it is even lower than in the

first one, 7 days earlier. Also in these far developed plants, how-
ever, we find an equal auxin content all over the stem, also in
the basal part, where the leaves had already dropped off for the
greater part. In this feature this experiment confirms the prece-
ding one.

The buds in the axils of the first leaf-pair, where they had an
average length of 1 mm excepted, the axillary buds had not
developed at any point of the stem, neither in this experiment,
nor in the preceding one.

In this experiment besides the auxin content of the stem, that
of the leaf-pairs was determined too. 10 7 weeks-old seedlings
of Lupinus albus were used for it. The plants were all in good
condition, had as an average 9 expanded leaves and from coty-
ledons to terminal bud measured 122 mm. The axillary buds had
not developed, except those of the lowest leaf-pair, 2 mm long
on an average. The auxin content was determined in: the terminal
bud including the 5th leaf-pair, the 4th, the 3rd, the 2nd and
the 1st leaf-pair, as well as of pieces of the stem 20 mm long,
that is of, a) and b) two successives pieces just below the ter-
minal bud, c) a piece half-way b)
and d), d) a piece just above leaf
2, and e) a piece just below it.
The results have been summarized
in figure 22.

Here too the auxin content of
the stem proves to be about the
same all along the stem; perhaps
the auxin content in the middle of
the stem actually was a little hig-
her than above or below it. On the
other hand the auxin content of
the leaf-pairs at the top of the
stem proves to be the highest; it
decreases gradually in basal direc-
tion. So the auxin content decreases
with increasing age.

Also in the experiments 22 and
23 in chapter VIII (p. 246) the
Figure 22. Auxin content ofnbsp;content of several parts of

older seedlings of Lupinus alhus the stem of mtact lupme-seedhngs
(experiment 19, 15/9/37).nbsp;was determined. These both expe-

riments made with seedhngs with on an average 6 expanded
leaves, point in the same direction. Here too, we fmd that at
different points of the stem the auxin content was equal. In
experiment 20 (p. 243), where the auxin content of the first and
the second leaf-pair was determined, it proved to be the highest
in the youngest leaf-pair too.

From these experiments it appears first, that the auxin content
of the stem of seedlings of Lupinus albus is about equal all along
the length of the stem. If the development of the axillary buds
should be connected with the auxin content of the stem, this
equal distribution of the auxin, would explain why in the intact
plants of Lupinus albus the axillary buds do not develop either
at the top nor at the bottom of the stem.

Only in the second series of experiment 18 we found an
extremely weak development of the axillary buds of the first
leaf-pair in far developed plants with an exceptionally low auxin
content of the stem.

We also found, that in young lupine-seedlings the auxin content
of the hypocotyl directly after the splitting of the cotyledons and
the first development of the plumule clearly shows an increase.
In far developed plants a decrease of the auxin content of the
leaves is found with advancing age. These last two facts make it
highly probable, in our opinion, that also in Lupinus albus the
terminal buds and the young developing leaves are production
centers of auxin. Dijkman (1934) and Jahnel (1937) believe, how-
ever, that in Lupinus albus such production centers of auxin are
lacking. We will discuss this further in § 3 of the next chapter
(p. 253).

In the experiments of chapter III we succeeded in inhibiting
the development of the axillary buds of decapitated seedlings of
Lupinus albus by application of aqueous hetero-auxin solutions.
We found at the same time that the degree of inhibition depends
on the concentration of the hetero-auxin applied. It seemed worth
while to repeat these experiments and to determine the auxin
content of the stem of these plants simultaneously, as this might
give us some information on the real nature of this phenomenon.

Of a set of 40 seedlings of Lupinus albus with on an average
4 expanded leaves the auxin content was determined of 8 plants,

b)nbsp;the 2nd leaf-pair, c) the 1st leaf-pair and d) in a 10 mm
section of the stem at the node of the 1st leaf-pair. The remaining
32 plants were decapitated 10 mm above leaf 1. After 5, 10, 13
and 14 days of every 8 plants the auxin content was determined
in the 1st leaf-pair and in a 10 mm section of the stem at the node
of the 1st leaf-pair. At the same time the lengths of the develo-
ping buds in the axils of the 1st leaf-pair were measured. When
determining the auxin content of the stem sections these axillary
buds were included; only in the last two determinations the buds
were large enough to be tested separately on their auxin con-
tent. The results of these determinations and of the measurings
have been summarized in table XXII and figure 23.

TABLE XXIL Auxin content and development of the axillary buds of
the first leaf-pair of seedlings of Lupinus albus decapitated 10 mm above
leaf 1. (experiment 20, 27/4/37—11/5/37).^_ ^

From these results it appears that the auxin content of the
stem at the node of the first leaf-pair clearly shows a decrease
after the decapitation. At the same time the axillary buds of the
first leaf-pair begin to develop. As is proved by the determination
of the auxin content, these buds in their turn begin to produce

Figure 23. Auxin content of 10 mm of the stem at the node of the first
leaf-pair and development of the axillary buds of the first leaf-pair of
seedlings of Lupinus albus decapitated 10 mm above leaf 1 (experiment
20, 27/4/37—11/5/37).

rather much auxin. It seems allowed to assume that this makes
the auxin content in the stem stop to decrease and even slightly
increase.

86 seedlings of Lupinus albus with on an average 6 expanded
leaves were used for this experiment. 80 of these were decapitated
20 mm above leaf 1 and to 30 of them a hetero-auxin solution
1 in lOquot;' was applied once a day via the cut surface, to 30 others
tap water, whilst no liquid was applied to the remaining 20.
6 plants were left intact. 4 days later of 10 plants in each series
and of the 6 intact plants the auxin content was determined in
a 10 mm section of the stem at the node of the first leaf-pair,
including the developing axillary buds. The length of these
axillary buds were measured simultaneously. On the 9th and the
16th day after the beginning of the experiment another lot of
10 plants from the 3, resp. 2 series, the auxin content was deter-
mined in a 10 mm section of the stem at the node of the first
leaf-pair. The auxin content of the developing buds was deter-
mined separately after measuring their lengths. The results of
these determinations and of the measurings have been summa-
rized in table XXIII and figure 24.

The results of the determinations of the auxin content teach
us first of all, that the auxin content of the merely decapitated
plants and of the decapitated plants to which tap water had been
applied is strongly reduced as compared to that of the intact
plants. It was taken for granted and indicated in figure 24 by
dotted lines, that the auxin content of the intact plants at the
beginning of the experiment is the same as 4 days later. When

TABLE XXIIL Auxin content of 10 mm of the stem at the node of the
first leaf-pair and development of the axillary buds of the first leaf-pair
of seedlings of Lupinus alhus decapitated 20 mm above leaf 1 (experiment
21, 1/6/37—17/6/37).

applying hetero-auxin 1 in 10' the reduction in the auxin content
is only very small, probably as a consequence of this auxin
supply. This only holds good for the results of the first 9 days,
however, for at the end of the experiment, 7 days later, the auxin
content of the plants with hetero-auxin 1 in 10' is but extremely
small, the plants with an application of tap water then showing
some increase again. It seems rather strange that the auxin con-
tent of the stem at the node of the first leaf-pair in the series
with hetero-auxin 1 in 10quot;' shows such a strong decrease at the

end of the experiment. Can this possibly be due to a transport
of the hetero-auxin to the basal parts of the stem or to inactivation
of the hetero-auxin? If, however, this low auxin content of the
stem in the application of hetero-auxin 1 in 10^ at the end of
the experunent is taken as a matter of fact, the simultaneous
increase of the auxin content in the series with tap water can
easily be ascribed to the higher auxin production by the axillary
buds in this series developing faster than in the series with
hetero-auxin 1 in 10^ These facts correspond with the results of
the analogous experiments of chapter III. It also appears from the
determinations of the auxin content of the buds separately, that
the buds which develop faster, contain more auxin than the
slower inhibited buds.

As in the former experiment a remarkable low auxin conteiit
was found in the stem when applying hetero-auxin 1 in 10=, it
was decided to repeat this experiment with an application of
hetero-auxin and tap water to more developed plants, so that
the application could take place above the second leaf-pair, the
auxin content thus being easily determinable at different points
in the stem.

For this experiment 70 seedlings of Lupinus alhus with on an
average 6 expanded leaves were used. The auxin content in 10
of these plants was determined of 10 mm sections of the stem
a) at the node of the second leaf-pair, b) below this node,
c) above the node of the first leaf-pair, and d) at this node.
After 3 days the remaining 60 plants were decapitated above
the second leaf-pair (15 mm above leaf 3), while the cotyledons
and the first leaf-pair were taken away. To 20 of these plants
twice a day an aqueous hetero-auxin solution 1 in 10'' was
applied via the cut surface, to 20 others tap water. The remaining
20 plants did not get anything at all. 8 and 9 days, respectively
14 and 16 days after the decapitation, of 10 plants of each series
the auxin content was determined exactly in the same way as
we did with the intact plants mentioned above. At the same
moment the length of both developing buds in the axils of the
first and second leaf-pair was measured. The auxin content of
these buds was determined together with the stem parts at the
nodes of the leaf-pairs. Only in two cases the buds were large
enough to determine their auxin content separately. The results

	10.6°! 0.9°
t' I.; ; I
	n.5°ti,o'
	^ O.Squot;

From these data it appears in the first place, that the growth
of the axillary buds at application of hetero-auxin 1 in 10® is
extremely small. By supply of tap water, however, there is a
marked development and the development is still stronger when
no liquid is supplied at all. Parallel to this the auxin content
appears to be rather high all over the length of the stem as
well in the intact plant as in plants to which hetero-auxin 1 in
10quot;' was supplied. In plants supplied with tap water this content
is lower and in the merely decapitated plants still less. From
the fact that the auxin content is higher with supply of tap
water than without any liquid can be concluded that the water
supply has favoured the auxin production of the plant. It is
striking that only the axillary buds of the first leaf-pair are
developing, while those of the second leaf-pair do not show any
development, unless tap water is supplied.

The preceding experiment was once more repeated, but this
time with application of hetero-auxin solutions of various con-
centrations. The number of determinations of the auxin content
which could be made on the same day being limited, we had
to take a smaller number of stem parts, of which the auxin
content had to be determined, when the number of experimental
series was extended. For this reason the plants were decapitated
above the first leaf-pair. 130 seedlings of Lupinus albus were
used with on an average 6 expanded leaves, internodes 1 and 2
were well developed, the terminal bud being found just above
leaf 4. The auxin content was determined in 10 of these plants,
of 10 mm sections of the stem a) at the node of the second
leaf-pair, b) just below this node, c) above the node of the
first leaf-pair and d) at this node. 8 days later the remaining
120 plants were decapitated 15 mm above leaf 1 and divided
into 4 series of 30 plants each. To 3 of these series an aqueous
hetero-auxin solution was applied twice a day via the cut surface
of the stem in a concentration of resp. 1 in 10\ 5 in 10® and 1
in 10®, and to one series tap water. 2, 9 and 16 days after the
decapitation the auxin content in every 10 plants of each series
was determined of a 10 mm section of the stem at the node
of the first leaf-pair, including the developing axillary buds and
of a stem part of 10 mm just below it. At the same time the
lengths of the developing axillary buds were measured. At the

Figure 26. Auxin content of the stem and development of the axillary
buds of the first leaf-pair of seedlings of Lupinus albus decapitated 15 mm
above leaf 1, at application twice a day of hetero-auxin 1 in lO'^, 5 in 10»
and 1 in 10«, and tap water via the main stem (experiment 23, 12/7/37—
5/8/37).

Figure 27. Auxin content in sections of 10 mm of the stem at the node
of the first leaf-pair (1) and of 10 mm of the stem below this node l2),
and development of the axillary buds of the first leaf-pair of seedlings of
Lupinus albus decapitated 15 mm above leaf 1, at application twice a day
of hetero-auxin 1 in 10» (A), 5 m 10« (B), and tap water (C) via the
main stem (experiment 23, 12/7/37—5/8/37).

time of the determination of the auxin content, 16 days after
the decapitation, the axillary buds were large enough to have
their auxin content examined separately. The results of these
determinations and measurings are summarized in the figures
26 and 27.

First of all it appears from the determinations of the auxin
content in the intact plants that here too the auxin content all
over the stem is the same. When comparing the auxin content
of the decapitated plants, to which hetero-auxin or tap water
has been applied artificially, we see a strong decrease of the
auxin content when tap water is applied. — In figure 27 it was
taken for granted and indicated by dotted lines, that the auxin
content of the intact plant at the time of the decapitation was
the same as 8 days before. — When comparing the auxin content
of the plants of the different series, we find, that 2, 9 as well as
16 days after the decapitation, the auxin content of the series
with hetero-auxin 1 in 10' is the highest. It is distinctly less
in the series with hetero-auxin 5 in 10®, still lower in the series
with 1 in 10« hetero-auxin and reaches a very low value in the
series with tap water. The auxin content of the stem at the
node of the first leaf-pair is sometimes higher, in other cases
lower than that of the stem part 10 mm lower. The differences,
however, are small and on the whole we can say that the auxin
content at these two places is about the same for each series.
The values of the auxin content, found 16 days after the deca-
pitation, in all series are lower than those found on the 2nd
and 9th day. This may have been caused by a low reactivity
of the Auena-coleoptiles on the day, when the extracts were
tested.

As appears clearly from figure 27, the development of the
axillary buds is smallest in the series with the highest auxin
content of the stem and highest in the series with tap water,
that is: in the series where the auxin content was lowest. In
figure 27 this all is clear since the crossing of the lines, indica-
ting the auxin content of the stem at the node of the first leaf-
pair and those, indicating the length of the axillary buds shifts
to the left in the successive series: a lower auxin content of
the stem coincides with a faster growth of the axillary buds.

The experiments discussed in this chapter clearly prove, that
the application of aqueous hetero-auxin solutions to decapitated
seedlings of Lupinus albus brings about a higher auxin content

of the stem, than when tap water is applied or no liquids at all.
From experiment 23 it also appears that this auxin content,
within certain limits, corresponds with the concentration of the
applied hetero-auxin solutions. At the same time we see, just
as in the experiments treated in chapter III (p. 218), that the
development of the axillary buds is inhibited by the application
of hetero-auxin. The only conclusion from these two observations
— in addition to those on the auxin content of the intact plant,
discussed in this chapter and the previous one — is, a) that
the growth of the axillary buds is inhibited if the auxin content
of the stem is high, and b) that when this auxin content decreases,
this inhibition decreases too. These results thus seem to endorse
the supposition of Thimann and Skoog (1934) that this correlative
inhibition is caused by a direct action of the auxin, and especially
also the idea of Thimann (1937) that this inhibition is proportional
to the concentration of the auxin.

As has been demonstrated, however, in chapter I, § 3a and 3f
(p. 187 and p. 198) already, some serious objections may be
moved against this quot;directquot; theory. Further it appears from
our experiments that the phenomenon is not mastered only by
the direct effect of a too high auxin content of the stem. If the
supposition of Thimann and Skoog would be right, a high auxin
concentration should be present in the inhibited buds. Our
experiments, however, show — as do also the experiments of
Thimann and Skoog (1934) themselves — that inhibited buds
contain, or give off, less auxin than buds, which are not inhibited.
Besides, our experiments with decapitated plants, to which tap
water was applied, or no liquid at all, teach that parallel with,
and probably as a consequence of the development of the
axillary buds, the auxin content of the neighbouring stem-parts
increases. This increase, however, does not cause again inhi-
bition of the growth of the axillary buds, as one should expect
when agreeing with the theory of Thimann and Skoog. The
results of experiment 22 do not fit entirely in the quot;directquot;
theory either.

In the first place the axillary buds of the first leaf-pair develop
in all series inversely proportionate to the auxin content of the
adjoining stem parts. The axillary buds of the second leaf-pair,
however, do not develop — excepted to a slight degree in the
tap water series — although the auxin content for each series
is about the same all over the stem. It is also striking, that the
tap water series was the only one in which some development
of the axillary buds of the second leaf-pair was observed. In

this series, however, the auxin content of the stem was distinctly
higher than in the series without application of any liquid.
Another accompanying feature is that the auxin content of the
stem is increased by the application of tap water, as compared
with plants without any supply of hquid. The application of
tap water to these decapitated plants therefore must have pro-
moted their auxin production.

Summarizing the results obtained so far, we can say that
there is some correlation between the auxin content of the
stem and the inhibition of the lateral buds, but a direct action
of the auxin on the growth of these buds seems rather im-
probable. The experiments of the next chapter will show with
certainty, that as far as the growth of lateral shoots is concerned
a direct action does not occur.

This question was earlier investigated by Dijkman (1934) and
Jahnel (1937), who both concluded that an auxin producing
center is absent in Lupinus. Our own investigations, however,
point in a different direction, and a closer examination of the
experiments by Dijkman and Jahnel tought us, that their con-
clusions are rather premature and can easily be attacked.

Dijkman as well as Jahnel determined the auxin content of
the plants by means of the diffusion method. As already has
been explained in chapter II, § 3 (p. 203), this method is less
reliable than the extraction method. In the diffusion method
one is always dependent on the readiness with which the
plant part gives off its auxin and this need not necessarily be
the same for the various parts, of which the auxin content
has to be determined. It is proved to be possible to indicate
the presence of auxin by the way of extraction in places,
where this was said not to occur on account of results ob-
tained by diffusion.

Dijkman (1934) working with dark -grown seedlings of Lu-
pinus alhus, decapited a number of 6 days-old seedlings just
below the cotyledons and found the growth of the hypocotyl
during the first 2 tot 3 days about equal to that of intact plants.

After that period growth stopped entirely whereas in the
intact plant the hypocotyl then still increases very rapidly
in length. When decapitating 2 days-old seedlings just above
the cotyledons the growth of the hypocotyl, for the following
7 days, is equal to that of intact plants. It is obvious, that in these

etiolated seedlings the cotyledons contain a stock of auxin
materials. Biut though Dijkman could show the presence oi
auxin in the epicotyl, in the etiolated leaves and in various
sections of the hypocotyl, he does not succeed in gettmg some
auxin by diffusion from the cotyledons. From this he conclu-
des, that auxin-producing centers are absent in Lupinus, and that
the' cells of the growing parts apparently are capable of pro-
ducing their own auxin.

Jahnel (1937) removed the terminal bud, one cotyledon or
both cotyledons of young seedlings of Lupinus albus growing
in the open air, and as a consequence of this he found a
slight decrease in growth of the hypocotyl for the next two
days. This decrease was strongest when the two cotyledons
and the terminal bud had been removed. When applying auxin
by means of orchid-pollinia no retarding of growth occurred,
excepted when the terminal bud had been taken away. Jahnel
thinks, that this retardation is not due to lack of auxin, but
to the checking of the supply by the cotyledons of nutritive
matter. The removal of any auxin-producing center, accor-
ding to him, already should show its effect directly after the
decapitation and to a much higher degree. His observations,
however, do not last longer than 48 hours after the decapitation,
whilst, in our opinion, the auxin present in the hypocotyl
is sufficient to enable the only slightly retarded growth to
go on during this time. Dijkman (1934) did not find a distinct
influence of the removal of cotyledons and terminal bud either
until on the second or third day afterwards. Jahnel also de-
termined the auxin content of different parts of the plant.
His figures are too irregular to enable to conclusive comparisons.
From the cotyledons he could obtain but very little auxin.
Young leaves gave of more auxin than older ones and on the
whole he found an equal distribution of auxin in the hypo-
cotyl. In the stem the auxin content was higher in the higher
sections than in the lower ones. From the terminal bud he could
get relatively little auxin. This does not justify his conclusion,
however, that actually no auxin producing center is present

In our experiment 16 (p. 239) the presence of auxm m the
cotyledons of Lupinus albus was proved by means of the ex-
traction method, although the quantity of auxin was not large.
Further this experiment showed that directly after the split-
ting of the cotyledons and the developing of the plumule,
the auxin content of the hypocotyl increased. This already

suggests that in Lupinus the plumule, which proved to con-
tain a considerable quantity of auxin itself, is a production
center of auxin. Besides, in experiment 19 (p. 241) the auxin
content of the successive leaf-pairs of well-developed plants
decreases with advancing age. Particularly the terminal bud
and the young leaves are rich in auxin and therefore must be
considered as production centers. The final proof, however,
that in Lupinus albus production centers of auxin actually
occur is given by the experiments mentioned in this chapter.
In the experiments 20, 21, 22 and 23 (p. 243) after the removal
of the terminal bud or of the shoot above the first or second
leaf-pair, the auxin content of the stem part just below regu-
larly and clearly shows a decrease. This decrease does not
change into an increase again until lateral buds are developing.
The only possible explanation of these facts is that in Lupi-
nus albus too the terminal bud and the young leaves are pro-
duction centers of auxin, and that the removal of these produc-
tion centers makes the auxin content of the stem decrease.
It does not increase, until the developing lateral buds start
to act as new production centers.

Since the extraction method actually showed the presence
of auxin in the cotyledons of Lupinus alhus, the continued
growth of the hypocotyl after decapitation just above the co-
tyledons as observed by Dukman — whilst after decapitation
under the cotyledons the growth after two days stopped —
can easily be explained by accepting that, during these early
stages, auxin is delivered by the cotyledons of Lupinus alhus.
By van Overbeek (1932) a similar auxin production by the
cotyledons was found in seedlings of Lepidium and Raphanus.

The presence of production centers in Lupinus does, of course,
not exclude that other parts of the plant too may be capable
of forming auxin. So, for instance the tip of the Auem-coleoptile
normally is the auxin production center but after decapitation
lower zones of the coleoptile prove to be able to produce
auxin too. Exactly the apparent lack of a similar physiological
regeneration of the production center in Lupinus albus makes
that, in our opinion, the own production of auxin by other parts
cannot play an important part.

appeared already that the auxin content of slowly developing
(inhibited) lateral buds was lower than that of fast developing
ones. It was difficult, however, to get comparable results in these
experiments. If the buds were still very small they could not
be extracted separately, and also in better developed buds it was
not possible as yet to determine the auxin content of successive
sections, so that only the auxin content of buds of unequal length
could be compared. If, however, we determine the auxin content
of inhibited lateral shoots, one is enabled to determine the auxin
content of successive sections and besides, in intact two-shoot
plants, we can compare the auxin content of the inhibiting and
of the inhibited shoot. The determination of the auxin content
of intact two-shoot plants and of two-shoot plants with an artifi-
cially inhibited lateral shoot, looked promising for the explanation
of the correlative inhibition of lateral buds and shoots.

In 9 plants of Lupinus albus, decapitated above the first leaf-
pair, both axillary shoots had developed, but widely differed in
length. Of these 9 two-shoot plants, which were of about the
same habit, the auxin content was determined in a) 10 mm of
the base of the longer lateral shoot, b) 10 mm of the stem above
a), c) 10 mm of the base of the shorter lateral
shoot, d) 10 mm of the stem above c) inclu-
sive the apical bud, e) 10 mm of the main
stem between both lateral shoots and f) 10
mm of the main stem below e); the average
of the stem from the base to the apical bud
of the longer lateral shoot being 23 mm, of
the shorter one 11 mm. The results of these
determinations have been summarized in fi-
gure 28 and show that the auxin content of
the shorter quot;inhibitedquot; shoot is lower per
length unit than that of the longer quot;inhibitingquot;
shoot. The auxin content of the main stem
was of the same order as that of the longer lateral shoot.

1) This experiment too was published already in a previous paper
(Ferman, 1938).

plants of Lupinus albus, with lateral shoots of unequal length,
but of about the same habit, the auxin content was determined,

namely of 3 successive stem parts of
10 mm of the base of the longer lateral
shoot, one stem part of 10 mm of the
base of the shorter lateral shoot and one
part of 10 mm of the main stem between
both lateral shoots. In these plants the
longer lateral shoot had an average
length of 52 mm, the shorter one of
15 mm. The results of these determina-
tions have been summarized in figure 29.

Here too, the auxin content of the
longer lateral shoot is much higher than
that of the shorter one; the auxin con-
tent of the main stem between both late-
ral shoots being about between these two.

For comparison with the two preceding experiments, the auxin
content of a number of two-shoot plants with lateral shoots of
about the same length was determined too. Two sets of 10 plants
were used, each set consisting of plants of about the same habit.
Of the first set, the length of the one, as well as of the other
lateral shoot was on an average 21 mm; the number of expanded
leaves was 5 on an average. For the second set of plants these
figures were resp. 44 mm and 6. The auxin content of these
plants was determined in stem parts of 10 mm, this being in the
first set of two, in the second set of three successive sections
from the base of both lateral shoots, and further of a part of
the main stem between both lateral shoots and of a part just
below it. The results have been summarized in figure 30.

Figure 30. Auxin content of two sets of two-shoot plants of Lupinus albus
with shoots of equal length (experiment 26, 14/7/37).

Though some deviating values occur, the general impression,
obtained from these determinations, for both sets is that the auxin
content of both lateral shoots of the same length is about equal.
In both sets the auxin content of the main stem is higher than
that of the lateral shoots.

§ 2. The auxin content of quot;two-shoot plantsquot; of Lupinus alhus
with artificially inhibited lateral shoot.

In the experiments discussed in chapter V (p. 226) the growth
of one of the lateral shoots of two-shoot plants of Lupinus alhus
was artificially inhibited by application of hetero-auxin solutions
via the decapitated other lateral shoot. These experiments were
repeated and at the same time the auxin content of the plants
was determined.

For this experiment 12 two-shoot plants of Lupinus alhus of
an almost uniform habit were used. In 4 of these plants the auxin
content of two successive stem parts of both lateral shoots of
respectively 5 and 10 mm and of a part of the main stem between
both lateral shoots, 10 mm long, was determined. The average
length of the stem from the base to the apical bud of the longer
lateral shoot was 24 mm, that of the shorter one 12 mm. The
remaining plants were divided into two series of 4. In both series
the longer lateral shoot was cut off at 10 mm above its insertion
and in one of these series once a day a hetero-auxin solution
1 in lOquot;' was supplied to cut surface of this shoot. On the first

TABLE XXIV. Growth of the shorter lateral shoot of two-shoot plants
of Lupinus albus (experiment 27, 4/5/37—10/5/37).

day and after 3 and 6 days the length of the remaining shoot
was measured. From table XXIV it appears, that here too the

growth of this shoot is inhibited strongly
by the application of hetero-auxin 1 in
lOquot;' via the decapitated longer shoot, as
compared with the blank controls.

Subsequently of two successive parts
of 10 mm of the shorter shoot of both
series the auxin content was determined.
The results of these and the preceding
determinations are shown in figure 31.

From the determinations of the auxin
content of the intact plant it appears
again, as in the experiments of the pre-
ceding section, that the auxin content of
the longer lateral shoot is higher than
that of the shorter one and that the
auxin content of the main stem is of
the same order as that of the longer
lateral shoot. It is remarkable, that in
the series where the growth of the shor-
ter lateral shoot is inhibited by hetero-
auxin 1 in 10' via the decapitated longer
shoot, its auxin content is again distinct-
ly less than in the series where the lon-
ger lateral shoot was merely decapitated
and the shorter lateral shoot was not inhibited in its growth.

The previous experiment was repeated once more with 40 two-
shoot plants of Lupinus alhus of about the same habit which
unfortunately were in a less vigourous state. The auxin content
in 10 of these plants was determined, a) of the terminal bud of
both lateral shoots, b) of the stem parts of the shorter lateral
shoot, c) of the upper and lower half of the stem part of the
longer lateral shoot and d) of a 10 nun section of the main stem
between both shoots. The average length of the stem of the
shorter lateral shoot was 7 mm, of the longer one 16 nmi. In
the same time the longer lateral shoot of 20 of the 30 remaining
plants was decapitated at 10 mm above its insertion. To 10 plants
an aqueous hetero-auxin solution 1 in 10' was applied twice a
day to 10 others tap water. The remaining 10 plants were left
intact. On the first day and after 6 and 14 days the length of

the lateral shoots was measured. The results of these measurings
have been summarized in table XXV. Probably as a consequence
of the unfavourable condition of the plants, the growth of the
lateral shoots in all the series was very slow. Yet it is striking,
how well the increase in length of the shorter lateral shoots in
the intact two-shoot plants agrees with that of the shoots with
the application of hetero-auxin 1 in 10'' via the decapitated
longer lateral shoot. Also the increase in length of the longer
lateral shoot in the intact two-shoot plants agrees well with that
of the shorter lateral shoot with the application of tap water.

Figure 32. Auxin content of
the shorter lateral shoot of
two-shoot plants of Lupinus
albus, a) intact plant, b) at
application twice a day via
the decapitated longer lateral
shoot of hetero-auxin 1 in
10', c) idem, at application
of tap water, d) intact plant
(experiment 28, 16/6/37—
30/6/37).

series was determined: in both series with decapitated longer
lateral shoots: that of the upper and of the lower half of the
stem of the shorter lateral shoot and of 10 mm of the main stem
between both shoots, and in the series of intact two-shoot plants:
that of the stem of the shorter lateral shoot, of three successive
parts of equal length of the longer lateral shoot and of 10 mm
of the main stem between both lateral shoots. The results of

these and the preceding determinations of the auxin content
have been summarized in figure 32.

The intact plants at the beginning of the experiment show
an equally high auxin content in the apical bud of the shorter
and of the longer lateral shoot, but the auxin content of the
stem of the longer lateral shoot was higher again than that of
the shorter one. The same is found in the series of intact two-
shoot plants 14 days later. The series with hetero-auxin 1 in 10®
compared to that with tap water shows that the main stem
between both shoots and the lower half of the shorter shoot in
the former have a rather high auxm content. A much lower
auxin content is found in the upper half of the shorter lateral
shoot. The auxin content found in the shorter lateral shoot and
in the main stem of the series with tap water is about equal to
that of the longer lateral shoot in the intact plants.

This experiment too is a replication of experiment 27. This
time we used 50 two-shoot plants of Lupinus alhus, all of them
with lateral shoots of unequal length. The auxin content was
determined in 10 of these plants of about the same habit: a) of
two successive parts of 10 mm of the bases of the longer and
b) of the shorter shoot and c) of a piece of 10 mm of the main
stem between both lateral shoots. The shorter shoot of these
plants was on an average 18 mm long, the longer one 31 mm;
the average number of expanded leaves of these shoots being
resp. 4 and 5. 7 days afterwards the remaining 40 plants were
divided into 4 series of 10 plants each, each series consisting as
much as possible of plants of the same habit. Of all these plants
the longer lateral shoot was decapitated 10 mm above its inser-
tion and an aqueous hetero-auxin solution 1 in 10® was applied

TABLE XXVL Growth of the shorter lateral shoot of two-shoot plants
of Lupinus albus (experiment 29, 19/7/37—2/8/37).

to these plants twice a day via the cut surface in two series;
in the two other series tap water was applied. On the first day,
and after 7 and 14 days the lengths of the lateral shoots were
measured. The results of these measurings have been summa-
rized in table XXVI.

In none of these series
the rate of growth of the
lateral shoots was high,
but here too in the series
with hetero-auxin 1 in
10'' the growth of the
shorter shoot was dis-
tinctly less than in the
series with tap water.

7 days after the deca-
pitation of the longer
shoot the auxin content
was determined in the
two series mentioned at
the top of the table, i.e.
a) in the series with he-
tero-auxin 1 in 10» of 3
successive parts of 10
mm of the shorter shoot
upward from its inserti-
on and b) in the series
with tap water also of
3 successive parts, 2 of
10 mm and 1 of 5 mm,
and besides c) in both
series of a part of 10
mm of the main stem
between both shoots and
d) of a part of 10 mm
just below. Again 7 days
later the auxin content
was also determined of
the plants of the two

other series i.e. a) of two successive parts of 10 mm of the
stem of the shorter lateral shoot upward from its base and
b) of a part of 10 mm of the main stem and of a part of 10 mm
directly below it. The results of these determinations have been
summarized in figure 33.

The longer shoots in the intact plants also here show a higher
auxin content than the shorter ones. The auxin content of Ijie
main stem corresponds to that of the longer lateral shoot. The
differences in the later determinations are only small, o^t still
a lower auxin content is found in the shorter shoots inhibited
by hetero-auxin 1 in 10' via the decapitated longer shoot than
in those of the series with tap water. Curious enough, a very
low auxin content was found in the main stem in the series
with hetero-auxin 1 in 10% whereas the experiments of the
preceding chapter showed that the auxin content is increased all
over the length of the stem by application of hetero-auxin 1 in
10'' via the decapitated stem.

It seems likely that here the auxin has been inactivated or
moved to lower sections of the stem.

Finally an experiment was made, with a number of two-shoot
plants of Lupinus albus with lateral shoots of unequal length in
which the shorter shoot, and not the longer one, was decapitated.
We now tried to inhibit the growth of the longer shoot by appli-
cation of hetero-auxin 1 in lOquot;' via the shorter one. 50 plants
were divided over 5 series of 10 plants, each series with plants
of about the same habit. In 4 of these series the shorter lateral
shoot was decapitated 10 mm above its base and twice a day
an aqueous hetero-auxin solution 1 in lO'^ was applied via the
cut surface to two of the series and tap water to the two other
series In the 10 remaining plants the auxin content was deter-
mined one day later: a) of the terminal buds of both shoots
b) of the stem part of the shorter shoot, c) of the upper and

tartF XXVII Growth of the longer lateral shoot of two-shoot plants
otlupinus albus (experiment 30, 11/8/37-26/8/37).

Increase in
length in mm
after 7 or 15

days
(average of
10 plants)

26
44

lower half of the stem
part of the longer lateral
shoot, d) of 10 mm of
the main stem between
both shoots and of 10
mm directly below it.
This series consisted of
smaller plants than the
other series; the shorter
shoot had an average
length of 11 mm, the lon-
ger one of 18 mm; the
average niunber of ex-
panded leaves was resp.
3 and 4. Just before the
decapiation of the shor-
ter shoot and 7 and 15
days afterwards the
length of the lateral
shoots was measured in
the 4 other series. The
results of these measu-
rings have been summa-
rized in table XXVII.

From this, it appears
that it is also possible
to inhibit the growth of
the longer lateral shoot
by an application of he-
tero-auxin 1 in 10'' via
the decapitated shorter
lateral shoot. During the
first 7 days the diffe-
rence is not yet very
distinct, but after 15
days we find that the
increase in length of the
longer lateral shoot in
the series with hetero-
auxin 1 in 10quot;'' is deci-
dedly less than in the
series with tap water.
The small difference af-

ter the first 7 days — which is in contrast with the preceding
experiments — is quite understandable, since here the growth of
the strongly growing longer lateral shoots had to be inhibited,
whereas in the preceding experiments the growth of the shorter
lateral shoots was influenced, which had already been inhibited
by the longer lateral shoot before.

On the 7th day after the decapitation the auxin content was
determined of the plants of the 2 series, mentioned at the top
of the table, on the 15th day of the two last-mentioned series,
always of 3 successive stem parts of 15 mm of the longer lateral
shoot from its base upward and of two successive parts of 15 mm
of the main stem from the insertion of the highest lateral shoot
to the base. The results of these and the preceding determinations
have been summarized in figure 34.

The auxin content of the intact two-shoot plants again perfectly
agrees with the results of the previous experiments; only the
higher auxin content in the terminal bud of the longer lateral
shoot, as compared to that of the shorter one differs from the
results of experiment 28. 7 days after the decapitation of the
shorter shoot there is little difference in the auxin content
between the series with hetero-auxin 1 in 10' and with tap
water. The auxin content of the longer shoot in the former
series is slightly lower than that of the second series; this again
runs parallel with the growth of the longer shoot, which in
the first series was but little less than that in the second series.
In both series, in which the auxin content was determined 14
days after the decapitation, the difference between the lower
auxin content of the longer shoot in the series with hetero-auxin
1 in 10quot;' and the higher auxin content in the series with tap
water is much more pronounced than 7 days before. As we have
seen already, just during these last 7 days a distinct difference
in growth of the longer lateral shoot was found between the
two series.

The results of the experiments discussed in this chapter clearly
show in the first place that in intact two-shoot plants of Lupinus
albus with lateral shoots of unequal length, the auxin content
per length unit of the longer shoot is higher than that of the
shorter one. The large number of determinations made on this
subject, all yielded the same results and place the phenomenon
beyond any doubt. The auxin content of the adjoining part of
the main stem in these plants generally was of the same order

of magnitude as that of the longer shoot, sometimes a little
lower, but still always higher than that of the shorter shoot.

We also observed that in two-shoot plants of Lupinus alhus
with lateral shoots of equal length, the auxin content of both
shoots was about the same and that of the main stem higher
than of each of the shoots separately.

The determinations of the auxin content of two-shoot plants,
of which the growth of one of the shoots had been inhibited by
application of hetero-auxin 1 in 10' via the decapitated other
shoot, yielded less uniform results. On the whole, however, the
auxin content of the inhibited shoot was found to be lower
than that of the uninhibited shoot from the series in which —
via the other decapitated, lateral shoot — tap water had been
applied or no liquid at all. These results were not only obtained
with plants where the growth of the shorter shoot was inhibited,
but also in plants where we succeeded in inhibiting the growth
of the longer lateral shoot by application of hetero-auxin 1 in
10' via the decapitated shorter shoot. It is remarkable that we
did not find an increase of the auxin content of the main stem
just below the insertion of both lateral shoots after the applica-
tion of hetero-auxin, as was the case in the experiments dis-
cussed in the preceding chapter. Only in experiment 28 this
was actually the case, but there, as an exception, the auxin con-
tent of the base of the shorter shoot was higher in the series
with hetero-auxin 1 in lO' than in the tap water series.

These experiments clearly show that it is highly improbable
that either in the intact two-shoot plant, nor in two-shoot plants
with artificial inhibition of one of the shoots, auxin is transported
from the inhibiting shoot into the inhibited one. Only for experi-
ment 28 some restriction must be made. The theory of Thimann
and Skoog (1934) and also that of Czaja (1935, 1935a), explaining
the phenomena of correlative inhibition by a direct action of
the auxin, postulates that the inhibition of lateral shoots is caused
by the transport of auxin from the inhibiting shoot into the
inhibited one. Since our results contradict this postulate, this
theory must be discarded.

We rather get the impression that there is a distinct relation
between the auxin content and the growth. In case of a low
auxin content we also find a slow growth, and reversely. When
the difference in auxin content is small, we also find a small
difference in the increase in length; a striking example of this
was given in experiment 30.

of correlative inhibition auxin is the correlation carrier. Since
a direct action of auxin in these inhibition phenomena is ex-
cluded, the question rises how to explain this inhibition — in
fact: a decrease of the auxin content in the inhibited parts. In
the next chapter a final discussion is devoted to this question.

A complete survey of the results of our successive experiments
is given in the Summary (p. 278). In broad outline these results are
the following. Application of hetero-auxin solutions to decapitated
seedlings of Lupinus alhus could inhibit the development of the
axillary buds, though not so completely as the terminal bud ^
left intact. As application of tap water causes no inhibition, it is
highly probable indeed that in this correlative inhibition of lateral
buds auxin is the correlation carrier. In this respect our experi-
ments corroborate the earlier experiments of Thimann and Skoog
(1933, 1934) with Vicia Faba. Also an application of lanolin hetero-
auxin pastes to decapitated seedlings of Lupinus alhus inhibits
the development of the axillary buds. In cuttings of Ligustrum
vulgare the application of aqueous hetero-auxin solutions only
caused a slight inhibition of the lateral buds and when lanolin
hetero-auxin pastes were applied, there was none at _ all.
Probably these woody cuttings had much difficulty in absorbing
the hetero-auxin from the lanolin pastes.

When measuring the lengths of the developing lateral buds of
decapitated lupine seedlings nearly always the axillary bud of
the second leaf proved to develop faster than that of the first
leaf from below, even though the average distance between the
insertion of the two leaves was only 2 to 3 mm. Besides it
appeared, when arranging the buds according to the rate of their
development, that the start which the faster developing shoot had
of the more slowly developing one, gradually increased. So here
too we apparently had again another case of correlative inhibition
as suggested already by DosTaL (1926) and Snow (1929). Our
later experiments proved indeed this to be the case. Here too
auxin proved to be the correlation carrier. If one of the two
lateral shoots was decapitated and a hetero-auxin solution 1 m
W was applied to the. stump the growth of the other shoot was
inhibited, whilst an aoplication of tap water or no liquid at all

failed to do so. We may tfierefore conclude that in the correlative
inhibition of lateral buds as well as in shoots, auxin is the
correlation carrier. Interesting as these results in themselves
may appear, they do not yet elucidate the actual character of
the activity of auxin in this inhibition. As has been said already
in chapter I (p. 180) different theories try to explain this
phenomenon.

The quot;indirect theoryquot; of Laibach (1933) and of Snow (1932,
1937), according to which the auxin primarily participates in a
growth process in the main stem and from this a secondary
effect inhibits the lateral buds and shoots, seems rather improb-
able to us. In this case some tissue capable to these growth pro-
cesses necessarily has to be present between the place of the
auxin production or -application, and the inhibited organ. In
our experiments with application of lanolin hetero-auxin pastes
to decapitated lupine seedlings, however, we found a strong
inhibition of the lateral buds as well when the hetero-auxin was
applied in the immediate surroundings of the buds, as when
applied at 12 mm higher up on the tsem. Neither did we find
in the latter case any indications of growth in length or of stem
swellings.

■ Our results when placing cut shoots of Lupinus albus and of
Pisum sativum seedlings in hetero-auxin solutions are somewhat
irregular. On the whole we found, as did Le Fanu (1936), that
the higher auxin concentrations inhibit the growth in length of
these shoots, as compared with their growth in tap water. So
auxin has a specifically inhibiting influence, when applied from
the base. To this kind of experiments there is the objection,
however, that in tap water too, the growth will soon stop,
probably in consequence of a deficient supply with nutrients, since
the growth of shoots of intact plants is always much stronger.
The auxin content of the shoots, placed in hetero-auxin, was
higher than of those, placed in tap water; so we must assume
that the auxin was transported acropetally with the transpiration
stream. This normally, however, does not occur as appeared from
a distinctly toxic effect of the hetero-auxin 1 in 10' on these
shoots.

The question rises whether in all these correlation phenomena
auxin, as assumed by Thimann and Skoog (1934) acts directly
and whether this direct activity must be ascribed to too high
a concentration of auxin (Thimann, 1937). In order to answer
this question, we determined the auxin content of a great
number of intact plants and of plants with lateral buds and

shoots artificially inhibited by application of hetero-auxin. We
found indeed in both cases a rather high auxin content all
along the entire length of the stem. After mere decapitation
and when tap water was applied, we found a lower auxin
content and, parallel with it, also a stronger development of
the lateral buds. Though this matches with the theory of
Thimann and Skoog, the fact that in inhibited buds a lower auxin
content was found than in the uninhibited ones, does not fit
in it. This conflict still becomes more urgent, when comparing
the auxin content of intact two-shoot plants and of two-shoot
plants of Lupinus albus of which one of the lateral shoots had
been artificially inhibited. In these two-shoot plants we always
found a distinctly lower auxin content in the inhibited than in
the inhibiting shoot. The auxin content of the main stem
appeared to match most with that of the inhibiting shoot. The
theory of Thimann and Skoog must therefore also be discarded.
Inhibition is not a consequence of too high an auxin concen-
tration, but rather of a too low one. These facts urged us to
explain this phenomenon of correlative inhibition in a different
direction. Already in a previous publication (Ferman, 1938)
mention was made of this.

In all our experiments we found that the auxin content in
the correlatively inhibited parts, in the axillary buds as well
as in the lateral shoots, is lower than in the uninhibited parts.
It is plausible that a slighter growth is the result of this. We
actually found a distinct parallel between the auxin content
and the rate of growth of the concerned parts. It is remarkable
in this phenomenon, however, that in this correlative inhibition
auxin is also the correlation carrier, as our experiments and
also those of others have clearly proved. This means that the
auxin, produced in the inhibiting organ, causes a lack of auxin
in the inhibited one. As our experiments have proved, there
cannot be any question of a direct effect of the auxin caused
by too high a concentration in the inhibited organ.

The only safe starting point, ascertained by our experiments,
is that in the inhibited organ the auxin content is lower and a
slighter growth the result of it. When moving the question on
which factor the production of auxin depends, we find as yet
but few data on this subject in the literature. In this connection
we mxust mention, however, the important investigation of Skoog

(1937) with coleoptiles of Avena deprived from their seed. He
found, that the formation of auxin in the tip of the Avena
coleoptile is dependent on some other substance (or substances)
which are transported from the seed to the tip in acropetal
direction. This substance, the nature of which still being un-
known, he calls auxin precursor. Schwanitz (1935), DosTaL
(1936, 1936a) and Went (1936) too found that in seedlings of peas,
rhizomes of Lathyrus and Agropyrum and tubers of Scrophu-
laria nodosa a substance or substances, necessary for the growth
of the shoots, is transported in acropetal direction. These data
are as yet rather vague, but if we assume that in all these
cases auxin is the limiting factor for the developing of the
organs concerned, we might conclude from it that yet another
factor is necessary for the formation of this auxin, which is
transported in acropetal direction to the place where the auxin
is formed.

The correlative inhibition of lateral buds and shoots can be
explained then in a simple and plausible way by means of the
following two hypotheses. First the assumption that in all these
cases a substance, or substances, are involved which are needed
in the production of auxin and which we, according to Skoog,
call the auxin-precursor. Secondly this precursor must be trans-
ported acropetally and particularly to the spots where the auxin
production is intensive, viz. where the precursor ^is quickly
converted into auxin.

During the first developmental stages of the young seedling
the precursor will be transported from the cotyledons acropetally
to the terminal bud and converted there into auxin. Subsequent-
ly this center of auxin production will attract the precursor at
an increasing rate. Consequently the terminal bud and the
young unfolding leaves, allready preformed in that bud, are
supplied with precursor. The dormant, hardly developed axillary
buds, however, remain deprived from precursor and therefore
cannot produce auxin. Since without auxin no growth, they
cannot grow out.

If the terminal bud is taken away, the quot;attractionquot; of the
precursor stops. The latter merely will accumulate at the apical
cut surface and also the young axillary buds will get a part of
it. They will convert it into auxin and consequently develop.

If one of the two developing axillary buds of the same leaf-
pair for some reason — e.g. by its slightly higher insertion on
the stem — gets a little more of the precursor than the other,
it will also produce more auxin. The more intensive production

of auxin by one of the lateral buds subsequently will attract
more of the precursor than the slower auxin production by the
other bud. The quot;inhibitionquot; exerted by one lateral shoot on the
other or by the terminal shoot on the axillary buds or lateral
shoots below thus is explained by the distribution of the pre-
cursor: the quot;inhibitingquot; shoot attracts the available precursor
and deprives more or less the quot;inhibitedquot; lateral bud or shoot
from it.

The remaining difficulty is how to visualize this quot;attractionquot;
of the precursor by the auxin. We might think of a chemical
balance, the precursor moving to the places, where it is con-
verted most rapidly and where, consequently, its concentration
is low. Another more plausible notion of this mechanism we
owe to Curtis.

In his survey on quot;The translocation of solutes in plantsquot;
CuTîTis (1935) mentions the probability that any treatment that
starts the activity of a group of cells in a shoot meristem may
also initiate the streaming activity of the conducting cells leading
to this particular region, thus establishing an active conductive
system connecting the meristem tissue with a supply of necessary
solutes. The supply of these solutes to the particular tissue
enables it to continue its activity and thus also to continue its
connection with the source of supply.

It does not seem unlikely that in our case the auxin is the
activator which effects the attraction of the auxin-precursor
together with that of other soluble substances.

Recent investigations by Thimann and Sweeney (1937) showed
an increase of the rate of protoplasmic streaming in the epider-
mal cells of the Auena-coleoptile brought about by hetero-auxin
at concentrations between 5 in 10' and 2 in 10quot;. It seems there-
fore in no way improbable that the auxin would have an
activating effect on the plasmic streaming of the conducting cells.

According to this, our conception is that the auxin produced
by the terminal bud and the growing leaves is given off to
the stem and will bring the cells where it arrives to a higher
activity and this, to a certain extent, proportionately to the
concentration of the auxin supplied. The results will be o.a. a
greater activity of the cells conducting the nutritive substances,
among which also the auxin precursor, to the growing parts.
The inhibited parts in the beginning will produce less auxin;
the cells, conducting the nutritive substances, therefore, will be
brought to a less high activity, and consequently a smaller
amount of precursor will be supplied to these parts. Once behind

Though this theory gives a rather plausible and simple expla-
nation of the phenomenon of correlative inhibition, still the
question remains how to explain in our experiments the iixhibi-
tion by artificial hetero-auxin supply. We can hardly assume
that here too, this hetero-auxin leads to a greater activity of the
conducting cells, for then the precursor, like in the decapitated
controls, would have to accumulate at the apical cut surface,
and this would have to result in a strong development of the
most apical axillary buds. This is not the case, however. For
that reason we believe the artificial inhibition must be explained
differently by assuming that in this case the supply with auxin
all over the cut surface of the stem, blocks up already in the
basal parts of the stem the tracks of the upward transport of
the precursor or at least seriously hampers the transport. Also
the growth inhibition, found when the cut shoots are placed
in hetero-auxin solutions and when hetero-auxin pastes are
applied to the morphologically lower side (Le Fanu, 1936; Snow,
1936), can be explained in a similar way. In both cases the appli-
cation of hetero-auxin — in concentrations as a rule probably
higher than those found in the intact plant — would block up
the upward transport of the precursor. The result then must be
a reduced auxin production and consequently a reduced growth
of the apical parts.

This theory, unlike the older ones, does not lead to controver-
sies, and further it has the advantage to match with the two
old and generally accepted hypotheses; a) the growth of the
aerial parts is — within certain limits — proportional to the
amount of available auxin, and b) the transport of auxin is
strictly basipetal.

Various experimental results, which formerly could not be
readily explained, fit well in this theory and can now be under-
stood. For instance the stronger development of the axillary
bud 2 (as compared to bud 1) in decapitated plants can be
ascribed to the fact that in the acropetal transport of the
percursor after decapitation, the latter is accumulated somewhat
more in the neighbourhood of the higher bud than in that of
the lower one. Even though this difference should be only very
slight at first, the somewhat stronger auxin production of the
higher bud would attract more of the precursor. Consequently
the bud being ahead in the first beginning can keep its start and
even increase this more and more.

The inhibition of the growth of cut shoots when placed in
hetero-auxin solutions, can be explained by our theory by assu-
ming that the high hetero-auxin concentrations in the base of
these shoots blocks up the transport of the precursor still present
there. These shoots therefore are more deficiently supplied with
precursor then the control shoots in tap water. The difference
between these two, however, can only be small since there is
but little precursor and we actually find only a sligth inhibition.
The growth of the shoots in tap water is also soon stopped,
which proves that other factors, probably nutritive substances
too, may soon act as limiting factors.

In experiment 26 with seedlings of Lupinus alhus decapitated
just above te second leaf-pair we found that the apical supply
with tap water promoted the auxin content of the stem already,
as compared with plants without water supply. Besides, the
axillary buds of the second leaf-pair also developed, though weak-
ly, in these plants which was not the case in any of the other
series. In our opinion this may be explained in this way that
the water supply to the stem promoted the upward transport
of the precursor and its conversion into auxin. This ready
upward transport of the precursor enabled the higher axillary
buds to develop too.

The fact that in all the other series only the axillary buds of the
first leaf-pair developed, proves once more that for the deve-
loping of the axillary buds a factor is needed, which comes from
the basal parts. Even if the axillary buds of both leaf-pairs
would receive an equal amount of this factor, the auxin precur-
sor, in the beginning, the axillary buds of the second leaf-pair
will already soon become deprived from precursor since by the
longer distance the effect of their attraction is smaller.

In intact two-shoot plants with lateral shoots of unequal
length the auxin content of the stem proved to be of about the
same value as that of the longer shoot. In our opinion this may
be caused by an auxin delivery by the longer shoot. This must,
according to our theory, also bring about —- at the place of
insertion of the two shoots — a higher activity in the cells of
the tracks of transport of the nutritive substances and precursor
in the direction of the longer lateral shoot than in the direction
of the shorter one. Consequently also this supply with nutrients
and with auxin precursor must be stronger in the direction of
the longer shoot. In two-shoot plants, where the growth of one
lateral shoot was inhibited by applying hetero-auxin via the
decapitated other shoot, this must be ascribed again to a blocking

up of the precursor supply of the intact lateral shoot by the
hetero-auxin in the main stem.

We leave undecided where exactly the auxin precursor is
produced and along which tracks of transport it is transported
upward. Further investigations will be necessary to shed more
light on this question and also on the nature of the auxin
precursor (or precursors).

When comparing this new theory, discussed in the preceding
section, with the older theories on the correlative inhibition
of lateral buds and shoots, one will find back in it several intems
of the older ones. One of the essential elements, the acropetal
transport of a substance, necessary for the formation of shoots,
is found already in Sachs' theory (1880, 1882), with this modi-
fication however, that we now assume, that this substance must
be first converted in the vegetation points into another sub-
stance, which is transported in basipetal direction and which
initiates the growth of shoots.

The opinion, upheld especially by Goebel (1903) and Loeb
(1915), that one has to deal here with the fact of one organ
depriving another of nutritive substances, we find back in
our theory in the attraction, exerted by the parts which are
activated by the auxin, on the transported nutritional sub-
stances and auxin precursor to those parts.

Their experiments and also those of Appleman (1918, 1918a),
Reed and Halma (1919), Child and Bellamy (1919, 1920), Harvey
(1920) and Denny (1926), all refered to in chapter I, § 1 (p. 180),
can be easily explained by assuming an acropetal transport of
an auxin precursor, which is interrupted by the various experi-
mental treatments and results into a development of the axillary
buds just below this interruption.

Our new theory also enables us to explain the experiments
of DosTâL and Snow (chapter I, § 2, p. 184). In the experiments
of DosTâL (1909, 1926) with leaf-pairs of Scrophularia nodosa
we must assume that at first the stream of nutritional sub-
stances and precursor was directed towards the leaves and that
only after the amputation of a leaf, its axillary bud was supplied
with these substances. The inhibiting influence of the leaves, the
axillary buds once developing, being only slight, as found by
DosTaL (1926), can be well understood since the developing
buds will produce more auxin and will exert a stronger attrac-
tion than the leaves.

The interesting experiments of Snow (1925—1937) are all
interpreted by him by means of an inhibiting influence, which
the terminal bud, the young leaves or some growth process in
the main stem exert on the concerned parts. All his experiments,
however, can be explained in a much simpler way than by
assuming that the inhibiting influence moves towards the inhibi-
ted parts, viz.: these parts remain deprived of a growth-promo-
ting influence, in the first place of auxin precursor. So we
should not see the phenomenon of correlative inhibition as an
inhibition of the growth, but rather as an absence of growth-
promotion. The attracting effect, exerted by the parts activated
by means of the auxin, on the substances wanted for their
growth, causes other parts to be deprived of these substances.

The experiments of Snow, in which his quot;inhibitingquot; influence
was weakened by a ringing of the epicotyl as far as the pith
(1925) or by decapitation or by removing the leaves of the
inhibiting shoot (1929), in our opinion must be explained as
follows. By the manipulation the auxin flow coming from the
inhibiting shoot is blocked up or weakened and consequently
also the attraction by this shoot. The result is that the previ-
ously inhibited parts in their turn can attract the nutritional
substances and precursor.

The fact, noticed by Snow (1931), that the axillary buds in
Pisum sativum first grow out to a certain length, before being
inhibited by the terminal bud, according to us, must be explained
as follows. The anatomical structure of the vegetation point of
Pisum sativum is such that in the terminal bud the young axil-
lary buds, at almost the same level with the terminal bud, also
receive some precursor; consequently they can produce some
auxin, develop to a slight degree and exert some attraction on
new precursor and nutritional substances. The terminal bud,
however, will constantly receive more precursor and thus be
able to exert a stronger attraction. By the growth of the terminal
shoot the axillary buds will get farther removed from the ter-
minal bud and no longer share any precursor simultaneously
with it. Therefore they will no longer be able to compete with
the strong attraction by the terminal bud. The consequence will
be that, after some time, the growth of the axillary buds stops.

According to Snow (1931) and Le Fanu (1936) the leaves of
a shoot will protect it against the inhibiting effect of another
shoot. According to us, however, the inhibition, occurring after
the removal of the leaves of one of the shoots, is the consequence
of the smaller auxin production and thus of a weaker attractio i

Our theory makes clear why cut shoots with removed leaves,
when placed in a hetero-auxin solution, are inhibited more
strongly than shoots with intact leaves. The shoots with leaves
will be better enabled to attract the precursor, which was
blocked up by the hetero-auxin (see preceding section), than
shoots without leaves.

The recent experiments by Snow (1937), to which we refered
on p. 200, too can be readily explained by means of our theory.
The experiment, in which the inhibiting influence of the one
lateral shoot would travel into the axillary bud of the other
shoot even up against the transpiration stream, can be explained
by assinning that the intact lateral shoot, when not yet deca-
pitated, attracts all nutritive substances available. After its
decapitation the axillary bud of the other shoot may succesfully
exert some attraction. In a following experiment the inhibiting
influence of one shoot would act on the axillary bud of the
other decapitated shoot, travelling down the growing shoot, up
and down through the halves of the split epicotyl and up through
the decapitated shoot. In this case we assume that the attraction
of the non-decapitated shoot, via the two halves of the epicotyl
also acts in the cotyledon of the half with the decapitated lateral
shoot. If not knowing the experimental results, we would not
have expected this. Our explanation, however, still is simpler
than that of Snow, who has to assume that his inhibiting in-
fluence acts in basipetal, in acropetal, in basipetal and again in
acropetal direction, whilst for us the only difficulty is, that we
must assume that in one half of the split epicotyl the attraction
is continued in basipetal direction.

Went's quot;diversionquot; theory (1936) has one important point in
common with our theory viz. the attraction, which the parts
activated by auxin are believed to exert on the transport of
other substances. Went (1936), however, describes these other
substances as two specific factors, necessary for the growth of
stem and axillary buds, and for the growth of leaves. These
factors should be clearly different from auxin. As we have
mentioned already, he fails to account for the fact that in the
intact plant no or only very little auxin is produced by the
dormant lateral buds, whilst their auxin production immediately
increases after decapitation of the terminal bud.

In two recent articles, which reached us just before the prin-
ting of this manuscript. Went (1938, 1938a) mentions a number
of interesting experiments which should prove the existence of

these specific substances. By removal of roots or cotyledons of
etiolated pea seedlings the growth of stems or leaves drops off
rather rapidly, indicating a rapid depletion of a factor necessary
for their growth. Went (1938a) concludes that the roots form,
and the cotyledons store to some extent a factor, required for
growth of the stem and proposes to call this substance caulo-
caline. Besides, Went finds indications for the existence of a
substance, necessary for the growth of the leaf, which he calls
phyllocaline. Together with the rhizocaline, necessary for the
formation of roots, they form a new group of phytohormones,
the quot;câlinesquot;. It is remarkable, that the activity of the caulo-
caline shows itself in promoting the growth in length, a quality
which formerly used to be ascribed to auxin. Therefore we
believe that the substance which Went calls caulocaline is ideii-
tical with the auxin precursor of Skoog (1937) and that this
substance does not promote the growth in length directly, but
only after its conversion into auxin in the vegetation point.
Only by assuming that an auxin precursor is involved, it becomes
possible to explain the correlative inhibition of lateral buds and
shoots. The explanation given by Went by means of his caulo-
caline is insufficient as we have already demonstrated. We are,
however, much pleased that the clever and remarkable inves-
tigations by Went (1938, 1938a) have given new indications for
the existence of such an auxin precursor.

In a recent publication Albaum (1938) mentions some experi-
ments with prothallia of Pteris longifolia, which are also im-
portant for the phenomenon investigated by us. He finds that
adventitious outgrowths only appear from cut pieces of these
prothallia when such pieces lack an actively growing meriste-
matic region of when a junction of dead cells lies between an
actively growing region and more basal regions. Auxin is sup-
posed to be transported from the apex through the cells of the
prothallium to the base. The auxin producing center of the
young sporophyte is the primary leaf. The latter produces auxin
which not only inhibits adventitious outgrowths from the
prothallium, but also the oudgrowth of other embryos. This
function of the primary leaf may be taken over by hetero-auxm

Albaum concludes from his experiments that the more active
apical regions draw up materials from less active basal regions
and use them in growth. According to him some relationship
appears between the supply of synthetic material and the pro-
duction of growth hormone. The inhibition of outgrowth of

adventitious prothallia or of more primary leaves he explains,
according to Thimann (1937), as an inhibition by too high a
concentration of auxin. A clear indication for this, however, he
does not find. It seems more probable to us, that here too we
have another case where by the activity of the auxin in the
apical region the nutritional substances and auxin precursor
are attracted from the more basal region.

Finally a few remarks on the investigations of van Overbeek
(1935), zimmermann (1936), GooDwiN (1937) and Delisle (1937).
They all find in herbs and trees with a high auxin production
of the terminal shoot a weak development of the lateral shoots
and in the case of a lower auxin production of the terminal
shoot, a strong development of the lateral shoots. This difference
in auxin production of terminal and lateral buds therefore
appears, by means of their correlative inhibition, to account
for the difference in structure of herbs, shrubs and trees.
According to us this difference in auxin production must be
ascribed by a difference in their supply with auxin precursor.
The question on which this depends in its turn, must be an-
swered by the anatomical structure of the young parts in their
earliest stages of development. The important question is which
parts at the start will receive more of the precursor. These
parts will be the first to convert it into auxin and by their
higher auxin production they will be able in future to attract
nutritional substances and auxin precursor at an increasing rate.
So finally the anatomical structure of the tracks of transport
in the young vegetation points determines the distribution of
the precursor, predestinates the result of the next competition
and therefore must be responsible for the external architecture
of plants.

1.nbsp;The development of the axillary buds of seedlings of
Lupinus alhus decapitated above the first or second leaf-pair
was inhibited by applying — via the cut surface of the stem —
aqueous hetero-auxin solutions of a concentration of 5 in 10«
and 1 in lOquot;'; hetero-auxin concentrations lower than 1 in 10quot;
mostly had no inhibiting but rather a promoting effect on the
development of the axillary buds, as compared with their growth
when tap water was applied.

or thickening of the stem was observed as a consequence of
this hetero-auxin supply.

3.nbsp;In the series where the growth of the axillary buds of the
first leaf-pair was inhibited, as well as in the series where it was
promoted, the bud in the axil of the second leaf generally
developed faster than that in the axil of the first leaf, though
the mean distance between the insertion of both leaves is only
2 to 3 mm.

4.nbsp;In single-node cuttings of Ligustrum vulgare placed in
the greenhouse the development of the still dormant lateral
buds was weakly promoted by an application of hetero-auxin
1 in 10' and inhibited to a slight degree by the application
of hetero-auxin 1 in 10« via the apical cut surface, in compa-
rison with their development when tap water was applied;
without any supply of liquid the development of the buds was

5.nbsp;An application of lanolin hetero-auxin paste 1 in lO« to
seedlings of Lupinus albus decapitated above the first leaf-pair
caused an inhibition of the growth of the axillary buds. This
inhibition was as strong in an application in the immediate
surroundings of the axillary buds as when applied 12 mm higher
up to the stem.

6.nbsp;An application of lanolin hetero-auxin 1 in 10» as near
as possible to the still dormant lateral buds of smgle-node
cuttings of Ligustrum vulgare placed in the greenhouse did not
cause any inhibition of their development.

7.nbsp;In seedlings of Lupinus albus, decapitated just above the
first leaf-pair, with axillary shoots of different length (so called
quot;two-shoot plantsquot;) the growth of the shorter or of the longer
lateral shoot was inhibited by applying an aqueous hetero-
auxin solution 1 in 10= to the cut surface of the decapitated
second (resp. longer or shorter) lateral shoot, compared with
the growth of these lateral shoots when applying tap water

8 The growth of cut off shoots of Lupinus albus witn one
expanded leaf placed in a hetero-auxin 1 in 10' solution was
inhibited, as compared with the growth in tap water; a hetero-
auxin solution 4 in 10» and 1 in 10» caused no inhibition. In
shoots of plants with two expanded leaves a hetero-auxin
solution 1 in 10' already caused a very slight inhibition ot
growth, this inhibition being somewhat stronger with hetero-

obtained by placing the shoots of plants with 4 to 5 expanded
leaves (the scales included) in hetero-auxin 4 in 10quot;, as com-
pared with the growth in tap water. The growth ^of the shoots
of intact plants, however, was much stronger.

10.nbsp;The development of the axillary buds of decapitated
shoots of Lupinus albus was not influenced by placing the
shoots in hetero-auxin solutions 1 in 10« and 1 in 10®, as com-
pared with the growth in tap water. In decapitated control
plants left in the soil, however, a much stronger development
of the axillary buds was observed. The auxin content at the
level of the first leaf-pair of the shoots in tap water was
distinctly less than that of the plants in the soil, whilst that
of the shoots in the hetero-auxin solutions was still higher.
At the same time a toxic effect of the hetero-auxin 1 in lO®
solution was observed.

11.nbsp;The auxin content of the stem of seedlings of Lupinus
alhus is about equal all along the length of the stem.

12.nbsp;In young seedlings of Lupinus alhus the auxin content
of the hypocotyl increases directly after the splitting of the
cotyledons and the first development of the plumule; the
plumule then contains a fairly considerable amount of auxin
too.

13.nbsp;In far developed plants of Lupinus albus the auxin
content of the leaves decreases with increasing age.

14.nbsp;The application of aqueous hetero-auxin solutions to
decapitated seedlings of Lupinus alhus via the cut surface of
the stem brings about a higher auxin content of the stem,
than when tap water is applied or no liquid at all. The auxin
content corresponds, within certain limits, with the concen-
tration of the applied hetero-auxin solutions.

15.nbsp;The application of tap water to decapitated seedlings
of Lupinus alhus increases the auxin content of the stem, as
compared with plants without any supply of liquid.

16.nbsp;The development of the axillary buds of the first leaf-
pair of decapitated seedlings of Lupinus albus is, within certain
limits, inversely proportionate to the auxin content of the main
stem.

17.nbsp;In seedlings of Lupinus alhus decapitated above the
second leaf-pair, in all series the axillary buds of the second
leaf-pair almost do not develop, whereas those of the first
leaf-pair do, though in each series the auxin content at both
levels of the stem is about the same.

19.nbsp;In decapitated seedlings of Lupinus alhus to which tap
water has been applied or no liquid at all, parallel with the
development of the axillary buds the auxin content of the
neighbouring stem parts increases.

20.nbsp;In intact quot;two-shoot plantsquot; of Lupinus alhus with
lateral shoots of unequal length the auxin content of the longer
shoot per length unit is higher than that of the shorter
shoot. The auxin content of the adjoining part of the main
stem generally is of the same order of magnitude as that of
the longer shoot, and always higher than that of the shorter
shoot.

21.nbsp;In intact quot;two-shoot plantsquot; of Lupinus alhus with
lateral shoots of equal length, the auxin content of both shoots
is about the same and that of the main stem higher than that
of each shoot separately.

22.nbsp;In quot;two-shoot plantsquot; of Lupinus alhus of which the
growth of one of the shoots has been inhibited artificially by
an application of hetero-auxin 1 in lO'' via the decapitated
other shoot, on the whole, the auxin content of the inhibited
shoot is lower than that of the uninhibited shoot of two-shoot
plants in which — via the other decapitated, lateral shoot —
tap water has been applied or no liquid at all.

1.nbsp;In the correlative inhibition of the development of lateral
buds and shoots auxin is the correlation carrier.

2.nbsp;In Lupinus albus the terminal bud and the growing
leaves are production centers of auxin.

3.nbsp;As the auxin content of the inhibited organs is always
lower than that of the inhibiting ones, the theory of Thimann
and Skoog (1934), and also that of Czaja (1935, 1935a), pos-
tulating that the inhibition of lateral buds and shoots is caused
by a direct action of auxin transported from the inhibiting
shoot into the inhibited organ, must be discarded.

4.nbsp;As no indication has been found for the necessity of some
primary growth process — or stem thickenings and swellings
— in the main stem, from which, according to the quot;indirectquot;
theory of Laibach (1933) and Snow (1932, 1937), a secondary
influence would inhibit the growth of the lateral buds and
shoots, their theory is highly improbable.

5.nbsp;Besides, against the above-mentioned theories a serious
objection is that one has to assume that in the inhibition of

one lateral shoot by another, either auxin or an inhibiting
influence or substance from either shoot has to travel upwards
into the other one. It seems very improbable that two iden-
tical factors would be transported in opposite directions in
one and the same organ or even in the same cells.

6.nbsp;The quot;diversionquot; theory of Went (1936) does not give an
adequate explanation of the correlative inhibition of lateral
buds and shoots, as it fails to explain why no — or scarcely
any — auxin is produced by the lateral buds in the intact
plant, and why this auxin production immediately increases
as soon as the terminal bud has been eliminated.

7.nbsp;In a new theory on the correlative inhibition of lateral
buds and shoots, the production of auxin is assumed to depend
upon the supply of a precursor, or precursors, transported
acropetally and chiefly attracted to those spots where auxin is
most intensively produced. Consequently, those parts which
received a little more of the precursor than the other parts
in the beginning, by their originally higher production of auxin,
will continue to receive more of the precursor. Other organs,
such as young, hardly developed axillary buds, remain deprived
from the precursor and therefore dormant, since they cannot
produce auxin and consequently cannot grow out. In the same
way the quot;inhibitionquot; of lateral shoots is caused by too defi-
cient a supply with the precursor.

8.nbsp;In experiments with artificial (hetero-) auxin supply to
decapitated plants via the apical cut surface it is assumed that
this (hetero-) auxin supply prevents or seriously hampers al-
ready in the basal parts of the stem the upward movement of
the precursor in its tracks of transport. In the same way the
growth inhibitions caused by a hetero-auxin supply from a
place, morphologically below the parts concerned, are explained
as a blocking up of the upward transport of the precursor.

9.nbsp;Went's assumption of the existence of a new phytohor-
mone, called caulocaline, coming from the roots and necessary
for the elongation of the stem or lateral buds (Went, 1938,
193a) seems superfluous. The phenomena described by him
simply — and preferably — can be explained in terms of the
new precursor theory.

The investigations were carried out in the Botanical Labo-
ratory of the State University, Utrecht. My best thanks are
due to Prof. Dr. V. J. Koningsberger and Dr. M. H. van Raalte
for their interest in my work and their valuable criticism.

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Goebel, K., 1902. Über Regeneration im Pflanzenreich. Biol. Centr. bl. 22,
385—397.

Goebel, K., 1908. Einleitung in die experimentelle Morphologie der Pflanzen.
Leipzig, 1908.

Goodwin, R. H., 1937. The role of auxin in leaf development in Solidago
species. Am. J. Bot. 24, 43—51.

Gouwentak, C. A. and G. Hellinga, 1935. Beobachtungen über Wurzelbildung.
Med. Landh. hogesch. Wageningen 39, 1—6.

Harvey, E. N., 1920. An experiment on regulation in plants. Amer. Nat. 54,
362—367.

Heyn, A. N. J., 1935. The chemical nature of some growth hormones as
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1074—1081.

Hitchcock, A. E., 1935. Tobacco as a test plant for comparing the effecti-
veness of preparations containing growth substances. Contr. Boyce
Thomps. Inst. 7, 349—364.

Hitchcock, A. E. and P. W. Zimmerman, 1935. Absorption and movement of
synthetic growth substances from soil as indicated by the responses
of aerial parts. Contr. Boyce Thomps. Inst. 7, 447—476.

Jahnel, H., 1937. Über den Wuchsstoff in Lupinus albus und seine Vertei-
lung während einer Vegetationsperiode. Jb. wiss. Bot. 85, 329—354.

Jost L., 1893. Über Beziehungen zwischen der Blattentwicklung und der
Gefässbildung in der Pflanze. Bot. Zeit. 51, 89—138.

Jost, L. and E. Reiss, 1936. Zur Physiologie der Wuchsstoffe. IL Einfluss
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335—376.

Kögl, F., H. Erxleben, and A. J. Haagen Smit, 1934. Über die Isoherung
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225, 215--229.

Kögl, F. and A. J. Haagen Smit, 1931. Über die Chemie des Wuchsstoffs.
Proc. Roy. Netherl. Acad. Sei. 34, 1411—1416.

Kögl, F., A. J. Haagen Smit, and H. Erxleben, 1933. Über ein Phytohormon
der Zellstreckung. Reindarstellung des Auxins aus menschlichem
Harn. Z. physiol. Chem. 214, 241—261.

Kögl, F., A. J. Haagen Smit, and H. Erxleben, 1934. Über ein neues Auxin
(„Hetero-auxinquot;) aus Harn. Z. physiol. Chem. 220, 90—103.

Kögl, F., A. J. Haagen Smit, and C. J. van Hulssen, 1936. Über den
Einfluss unbekannter äusserer Faktoren bei Versuchen mit Avena
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Kögl, F. and D. G. F. R. Kostermans, 1935. Über die Konstitutions-Spezifität
des Hetero-auxins. Z. physiol. Chem. 235, 201—^216.

Koningsberger, C., 1936. De auto-inactiveering der auxinen. Thesis Utrecht,
1936.

Koningsberger. V. J. and B. Verkaaik, 1938. On phototropic curvatures in
Avena, caused by photochemical inactivation of auxin-a via its lactone.
Ree. trav. bot. néerl. 35, 1—13.
Laibach, F., 1932. Pollenhormon und Wuchsstoff. Ber. dtsch. bot. Ges. 50,
383—390.

Laieach F., 1933. Wuchsstoffversuche mit lebenden Orchideenpollinien.
Ber. dtsch. bot. Ges. 51, 336—340.

Planta 25, 648—659.
Laibach, F. and O. Fischnich, 1936a. Über Blattbewegungen unter dem Ein-
fluss von künstlich zugeführtem Wuchsstoff. Biol. Zentr. bl. 56, 62—68.
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' regeneration of Bryophyllum calycinum. Bot. Gaz. 60, 249—276.
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' curvature in the stem of Bryophyllum calycinum and the possibility
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Loeb, J., 1918. Chemical basis of correlation. 1. Production of equal masses
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Bot. Gaz. 65, 150—174.
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1924

Mai, G., 1934. Korrelationsuntersuchungen an entspreiteten Blattstielen mit-
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Sprossen. Arch. Entw. mech. 38, 584^681.
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Ha alte, M. H. van, 1937. On factors determining the auxin content ot the
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Schwanitz, F., 1935. Beiträge zur Analyse der pflanzlichen Polarität. Beih.
Bot. Centr. hl. A 54, 520—530.

Skoog, F., 1935. The effect of x-radiation on auxin and plant growth.
J. Cell. Comp. Physiol. 7, 227—270.

Skoog, F., 1937. A deseeded Avena test method for small amounts of auxin
and auxin precursors. J. gen. Physiol. 20, 311—334.

Skoog, F. and K. V. tramann, 1934. Further experiments on the inhibition
of the development of lateral buds by growth hormone. Proc. Nat.
Acad. Sei. 20, 311—334.

Snow, R., 1925. The correlative inhibition of the growth of axillary buds.
Ann. Bat. 39, 841—«59.

Snow, R., 1929. The transmission of inhibition through dead stretches of
stem. Ann. Bot. 43, 261—267.

Snow, R., 1929a. The young leaf as the inhibiting organ. New Phytol. 28,
345—358.

Snow, R., 1931. Experiments on growth and inhibition. I. The increase of
inhibition with distance. Proc. Roy. Soc. B 108, 209—223.

Snow, R., 1931a. Experiments on growth and inhibition. II. New phenomena
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Snow, R., 1932. Experiments on growth and inhibition. III. Inhibition and
growth promotion. Proc. Roy. Soc. B 111, 86—^105.

Snow, R., 1935. Activation of cambial growth by pure hormones. New
Phytol. 34, 347—360.

Snow, R., 1936. Upward effects of auxin in coleoptiles and stems. New
Phytol. 35, 292—304.

Snow, R., 1937. On the nature of correlative inhibition. New Phytol. 36,
283—300.

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Haferkoleoptile. Jb. wiss. Bot. 71, 184—213.

Thimann, K. V., 1934. Studies on the growth hormone of plants. VI. The
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Bot. 24, 407^12.

Thimann, K. V. and J. Bonner, 1933. The mechanism of the action of the
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Thimann, K. V. and F. Skoog, 1933. Studies on the growth hormone of
plants. III. The inhibiting action of the growth substance on bud
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Thimann, K. V. and F. Skoog, 1934. On the inhibition of bud development
and other functions of growth substance in Vicia Faba. Proc. Roy. Soc.
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Thimann, K. V. and B. M. Sweeney, 1937. The effect of auxins upon proto-
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' Proc. Roy. Netherl. Aead. Sei. 34, 875—892.
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' Ree. trav. bot. néerl. 29, 379—496.
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' Proc. Roy. Netherl. Aead. Sei. 36, 760—761.
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' Ree. trav. bot. néerl. 31, 810—«57.
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' Avena 'sativa. Proc. Roy. Netherl. Acad. Sei. 30, 10—19.
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'l—116. '

'Siol. Zentr. bl. 56, 449-^63.
Went, F. W., 1938. Transplantation experiments with peas. Am. J. Bot. 25,

'root formation. Plant Physiol. 13, 55—80.
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Zimmerman, P. W. and F. Wilcoxon, 1935. Several chemical grovrth sub-
stances which cause initiation of roots and other responses in plants.
Contr. Boyce Thomps. Inst. 7, 209—229.
Zimmermann, W. A., 1936. Untersuchungen über die räumliche imd zeitliche
Verteilung des Wuchsstoffes bei Bäumen. Z. f. Bot. 30, 209—252.

De theorie van Thimann en Skoog, volgens welke de correla-
tieve remming van de ontwikkeling van zij knoppen en zij sprui-
ten zou berusten op een directe werking van auxine, is niet
houdbaar.

Ook de theorie van Laibach en van Snow, volgens welke de
correlatieve remming van de ontwikkeling van zij knoppen en
zijspruiten zou berusten op een indirecte werking van auxine,
doordat van groeiprocessen, die door auxine worden aangezet,
een secundaire remmende invloed zou uitgaan, is weinig waar-
schijnlijk.

R. Snow, Proc. Roy. Soc. B 111, 1932, 86—105,
New Phytol. 36, 1937, 283—300.

Bij Lupinus albus fungeren de eindknop en de jonge bladen
als productie-centra van auxine.

De vorming van polyploïeden is een der oorzaken geweest
van het ontstaan van nieuwe soorten.

Bodmann beschouwt de klieren van het cyathium van Euphorbia
ten onrechte als marmelijke bloemen.

Uit de onderzoekingen van Trömer is gebleken, dat contractie
en geleiding bij het hart steeds gekoppeld voorkomen.

De kritiek door Brock uitgeoefend op het streven de enzymen
der Invertebraten door zuivering en gebruik van synthetische
substraten te vergelijken met die der Zoogdieren, en met andere
bekende enzymsystemen, is ongerechtvaardigd.

De kristallen door Beale aangetroffen in cellen van viruszieke
planten, behoeven nog niet identiek te zijn met het kristallijne
virus-proteïne van Stanley.

De door Leonian gevonden bevordering van de groei van
Phytophthora cactorum door stoffen, die door de wortels van
graanplanten worden afgescheiden, mag niet toegeschreven wor-
den aan de werking van een auxine.

Dat de plastiden onafhankelijk van kern en plasma zouden
muteren, is door Imai niet bewezen.

De onderzoekingen van Grüneberg en Emmens omtrent de
roughest^-inversie en -reïnversie in het X-chromosoom van
Drosophila melanogaster zijn te beschouwen als een afdoend
bewijs voor het bestaan van het z.g. positie-effect.

In het belang van wetenschap en maatschappij dient gestreefd
te worden naar een nauwe samenwerking tussen biologie en
landbouwkunde.

Het is voor Nederlands Oost-Indië van belang, dat ernstig
gestreefd wordt naar een groter binnenlands verbruik van grond-
stoffen, die thans vrijwel uitsluitend geëxporteerd worden.

Art. 1 van de Hoger-Onderwijswet houdt in, dat de Univer-
siteit aan toekomstige leraren naast een wetenschappelijke vor-
ming ook een paedagogisch-didactische opleiding tot het leraars-
ambt heeft te geven; deze opleiding geschiede niet na, maar
tegelijk met de wetenschappelijke vakstudie.

De beoefening van de theoretische biologie vereist enige logi-
sche en kennistheoretische scholing; het is de taak der Univer-
siteit daarin te voorzien.

: S	(1)

3 a
	CO




i 288	27(2)
1 419	9(1)

		Increase		in length			in	mm (average of 10 plants)
	first 13 days			next 3 days			next 4 days			next 3 days			next 4 days
At application twice a day via the main stem of	TS i 0 1	I i 1	quot;nb o ^^ M .2 45 -s..	■TJ o M	T) CA CO	O S-i	T) 0) ' 1	1 rO lt;1gt; w 03	o ^^ 1 w .2=3 ■s.. u	1 01 ^ o w	1 ^ w cc	13 M o w .2 43 -s..	13 3 ii quot;m	13 3 .a s 1	13 Sh 3 O 1 .2 43 i 1s .. t ^^
hetero-auxin 1 in 10^	3	4	7:10	3	6	6:10	7	8	9:10	14	17	8:10	16	26	6:10
hetero-auxin 1 in 10®	6	10	6:10	5	11	5:10	13	22	6:10	4	10	4:10	5	9	6:10
hetero-auxin 1 in 10'	'7	10	7:10	7	15	5:10	10	21	5:10	8	10	8:10	6	4	15:10
tap water	8	11	7:10	!2	15	8:10	19	23	8:10	7	13	8:10	7	15	5:10

At application onto the apical cut surface of	Length in mm (average of 10 cuttings)
At application onto the apical cut surface of	after	6 days	after 9 days	after 13 days after 15 days
lanolin hetero-auxin		2'/2	4	8V2	10
paste 1 in		2'/2		8V2
lanolin hetero-auxin		2	4	8V2	10
paste 1 in 10®				8V2
plain lanolin paste		3	51/2	91/2	IIV2

Placed with their basal ends in glass tubes with	Length in mm (average of 24 and of 12 shoots)
	internode 1			total length
	days after starting the experiment				Increase in length after 16 days
	0 3 1 6	1)	16	0 1 3 6 11 !6
hetero-auxin 1 in 10' tap w ater	- 1 - 112 - j - jl2	13 13	Hi 15	39 58 81 85! 89 43 65 93 94 96	50 53

	0 1	5 1	10	13	14
Terminal bud and not- expanded leaves	13,5quot;±1,5°	—	—	1	—
second leaf-pair	17,1°±1,9»	—	—	i —	—
first leaf-pair	; 3,2»±0,9quot;	8,0»±:,3»	4,1»±1,3»	—	9,1»±0,8°
axillary buds of the first leaf-pair	1 ~	-	-	4,0«±0,5lt;'	4,0''±0,6»
10 mm of the stem at the node of the first	: 19,0quot;±1,6«	6,5°±1,0quot;	S,l»±0,9'	4,9«±0,8°	5,8''±0,6quot;
leaf-pair	i

At application twice a day via the main stem of	Length in mm (average of 16 plants)
		after 8 days			j after 14 days
	bud 1		bud 2	bud 1 and bud 2 together	' bud 1 i	bud 2	bud and bud 2 together
hetero-auxin 5 in 10«	3		4	7	21	29	50
hetero-auxin 1 in 10«	8		10	IS	32	49	81
hetero-auxin 5 in 10'	13		15	28	55	72	127
hetero-auxin 1 in 10'	13		20	33	48	70	118
tap water	11		11	22	48	53	101

At application twice a day via the main stem of	Increase in length in mm				(average of 16 plants)
	first 8 days				next 6 days
	slower bud i	faster bud	ratio slo- wer : : faster bud	slower bud		faster bud	ratio slo- wer ; : faster bud
hetero-auxin 5 in 10«	3	4	7: 10		16	27	6: 10
hetero-auxin 1 in 10«	8	10	8: 10		23	40	6: 10
hetero-auxin 5 in W	13	15	9: 10		11	58	7:10
hetero-auxin 1 in lO''	13	20	7: 10		34	51	7: 10
tap water	9	n	7: 10		30	49	6: 10

At application twice a day via the main stem of	After 8 days			After 14 days
	length	in mm	number of plantswith developed cotyledo- nary buds	length	in mm	number of plantswith developed cotyledo- nary buds
	average of l6plants	total of 16plants	number of plantswith developed cotyledo- nary buds	average of 16plants	total of 16 plants	number of plantswith developed cotyledo- nary buds
hetero-auxin 5 in 10®	0	0	0	0	0	0
hetero-auxin 1 in 10®	2	25	3	7	104	6
hetero-auxin 5 in 10'	3	44	8	7	109	8
hetero-auxin 1 in 10'	2	28	5	4	58	6
tap water	0	0	0 1	4	68	7

At application twice a day via the main stem of	Increase in length m mm (average of 10 plants)
	first 15 days with application			next 12 days without application
	bud 1	bud 2	bud 1 and bud 2 together	bud 1	bud 2	bud 1 and bud 2 together
hetero-auxin 1 in 10»	1 5	4	9	30	31	61
hetero-auxin 1 in 10'	15	11	26	38	32	70
tap water	12 1	14	26	42	57	99

At application twice a day via the main stem of	Increase in length in mm (average of 10 plants)
	first 15 days with application			next 12 days without application
	slower bud	faster bud	ratio slo- wer : : faster bud	slower bud	faster bud	ratio slo- wer ; : fasterbud
hetero-auxin 1 in 10^	2	7	3: 10	9	52	2: 10
hetero-auxin 1 in 10'	10	16	6; 10	29	41	7: 10
tap water	9	17	5: 10	36	63	6: 10

	Increase		in length in		mm (average of 10 plants)
At application	first 15 days			next 6 days			next 10 days
twice a day via			ratio			ratio			ratio
the main stem of	slower	faster	slower:	slower	faster	slower:	slower	faster	slower:
	bud	bud	: faster	bud	bud	; faster	bud	bud	: faster
	bud		bud			bud			bud
hetero-atixin 1 in 10»	12	17	7: 10	25	37	7; 10	22	25	9: 10
tap water	16	26	6; 10	25	43	6: 10	24	29	8: 10

after 13 days			after 16 days			after 20 days			after 23 days			after 27 days
T-i	N	ll quot; So	T-l	IM	o 11	1-1		«a	i-i	N	0 « §0	T-l	CM	OJ S o
1	3 .J2	Xl		1		.a	3 XI	rH^	Xi	T)	X			«CV,
3	4	7	8	8	16	16	15	31	31	31	62	53	51	104
6	10	16	11	21	32	24	43	67	28	53	81	33	62	95
8	9	17	19	20	39	33	37	70	43	45	88	48	50	98
11	8	19	23	23	46	41	47	88	50	58	108	64	66	130

At application twice a day via the main stem of	1 u i iz	1 u 0) ■s	CQ -SI ^	T3 M O U T—t lt;D w Js CO O « (B •• U	T3 i a 1 w	IS 3 h ID w CO «4H	l\|	s- 3 O U I-H Q1 CO .2 45 -s..	13 3 M 1	1 3 1 42 ! ^ «4-1	W T3 J-t	Ti M O M m o o I-
								')
hetero-auxin 1 in 10«	! 5	9	14	5:10	7	15	22	3:10	11	30	41	3:10
hetero-auxin 1 in 10'	8	11	19	7:10	12	18	30	6:10	16	32	48	3:10
tap water	5	10	15	5:10	8	18	26	4:10	13	33	46	3:10
without supply of liquid	5	10	15	5:10	6	13	19	3:10	8	18	26	4:10

	Place of ap- plica- tion	Increase in length in mm (average of 10 plants)
At application onto the the cut surface of the		first 15 days with application			next	12 days without application
main stem of		bud 1	bud 2 i	bud 1 and bud 2 together	bud 1	bud 2	bud 1 and bud 2 together
lanolin hetero-auxin paste 1 in 10«	15 mm above	3	6	9	25	43	6S
plain lanolin paste	leaf 1	6	12	18	26	36	62
lanolin hetero-auxin paste 1 in 10quot;	just above	4	2	6	45	20	65
plain lanolin paste	leaf 2	10	3	13	46	19	65

At application as a ring around the stem at the insertion of the first leaf-pair of		Length in		mm (average of 10 plants)
			days after the decapitation
	13		19		26	30	34
lanolin hetero-auxin			57		124	149		172
paste 1 in 10«			57		124
plain lanolin paste	22		87		171	191		210

1		0,9 quot;t 0,3-

inlaclplant		J
-		——

1	1 1 1 ! 1 1 i...	1

ring around the stemfirst 13 daysnext f				) days	next 7	days next 4 days next 4 days
at the msertion ot tne first leaf-pair of	in mm	ratio	in mm	ratio	in mm	ratio	in mm	ratio	in mm	ratio
lanolin hetero-auxin paste 1 in 10quot;	14	6	43	1 7	67 1 1	! »	25	12	23	12
plain lanolin paste	22	10	Î 65	10	84	10	20	10	i i9	10

At application twice a	Length of the longer lateral shoot before	Length in mm (average of 10 plants)						Increase in length in mm
day via the decapitated longer lateral shoot of	its decapita- tion, in mm (average of 10 plants)	days after decapitation of the longer lateral shoot						after 18 dayj (average of
day via the decapitated longer lateral shoot of	its decapita- tion, in mm (average of 10 plants)	0	4 1	7	11	14	18	10 plants)
hetero-auxin 1 in 10®	13	4	5	5	7	8	9	5
hetero-auxin 1 in 10®	17	5	7	8	13	16	22	17
tap water 2/1_______	13	4	6	8	12	16	23	19

				0	3 ;	6	9	0	3 1	6	9	0	3	6	9
hetero-auxin	1	in	10^ —		6	7	9	43	60	65	84	1	! 1		2
hetero-auxin	4	in	10quot;	—	8	16	19	45	68	93	103	1	2	^ 2	3
hetero-auxin	1	in	10«	_	8	14	15	44	69	88	97	1	2	i 2	3
tap water				-	9	13	16	45	76	91	102	1 ^	2	; 2	3

days after starting the experiment										Increase in length
6	8	12	17	0	3	Ö	9	12	17	after 17 days
10	12	l,-5	13	41	55	76	85	87	91	50
11	12	14	15	37	60	84	90	92	100	63

At application once a day via the main stem of		Auxin content			Length of the axil- lary buds in mm (average of 10 plants)
At application once a day via the main stem of		days after the decapitation			days after the decapitation
		4	9 1	16	4	9 i	16
hetero-auxin 1 in 10^	axillary buds 10 mm of the stem	n.si' o.squot;	O.C O.Oquot; 5,1 »±0,4»	1,5»±0,6» 0,8»±0,2»	0	7	22
tap water	axillary buds 10 mm of the stem	4,6''±0,6''	2,0» 1,0» 0,5°±0,2»	3,1 »±0,6» 4,2»±0,5»	3	17	46
without application of liquids	axillary buds 10 mm of the stem	4,9»±0,5»	0,0»±0,0» 0,6quot;±0,2»	—	3	12	—
'ntact plant	10 mm of the stem 1	19,5'' 1,0»	—	—	0	—	—

	Length of the longer lateral shoot before its decapita-	Length in mm (average of 4 plants)			Increase in length in mm after 6 days (average of
	Length of the longer lateral shoot before its decapita-	days after decapitation of the longer lateral shoot			Increase in length in mm after 6 days (average of
	tion in mm j	0 '	3	6	4 plants)
At application once a day via the deca- pitated longer late- ral shoot of hetero- auxin 1 in 10»	39	20	21	22	2
Longer shoot only decapitated	30	17	20	23	6

At application twice a day via the decapita- ted longer lateral shoot of	Length in mm (average of 10 plants)			Increase in length in mm after 14 days (average of 10 plants)
	days after decapitation of the longer lateral shoot
	0 1	1 6 !	14
hetero-auxin 1 in 10quot;'	13	13	It	3
tap water	13	14	19	6
intact plant *)	6 (17)	7 (20)	8 (23)	2 (6)