136 CCXMNGIIAM OX FLUCïUATIO:XS IS TUEGF-SCENCE,
cf tlie lenves of seedling plaats are for some tii
to twopiuuto pi-eseut, and these bearing only a
probably much less iuQuential in them than it is
multitudinous pinnules,
The pheiioraena which are presented by thi
tripicftl conditions, and especially when grown
osteusioQ of root-surface, certainly render it vf
of deep depression of the primary petiole as a
Had it been present, it would have been quite a
the rule that the position of the Tarious parts of
is one which was either the permanent position ir
;e very feebly dev«loperi, there being only from o
very few paii-s of pinnules, so that distal leverage
in fully developed leaves with their four pinuto a
leaves of Mimosn pudiea, wlieu grown under norn
in the open ground so as to permit of indefin
•y hard to imasine how a belief in the ocourrer
nonnal nyctitroi'ic phenomenon should have arisf
joiualous aud a striking example of an exception
lyctitropio leaves during the earlier part of the nig
:y young leaves or the diurual position in son
what older but still immature ones. But, as a matter of fact, deep petiolar dei
.nd the slightly ascending, horizontal, or slightly descendin
s not c
>3Ìtion which really does c aiîords
mple, not of doviatio but of conformity to,
that
plants with unlimited extension of root-surfu(
one owing to the coinoideut depression of osmotic capaoit;
when they have still to contend with very considerable distal
disturbaooes, which are quite incapable of inducing deep deprt
to solar stimulation, readily sufSce to give rise to it now. A
I the liquid-equilibrium in an axis which
ule. The pos'.tio
C, the disturbani
c-stromity gives
dei^ression when
lomes into play
ithii
has
normally an extremely unstable
the pulvinar tissues at a time
and heoce very slight
iu unloaded leaves exposed
:en pointed out in Ajipondi.'c
the amputation of its distal
ach more constant and extensively propagated petio
t occurs after the leaves have assumed the initial noDtiiroal position thm
vhilst they are still sabject to solar stimulation and in tlie maximal diurnal one.
iplanation of the origin of the belief ; for it is conceivable that deep petiolar
liepression may spontaneously occur in
abnormally dry nootumal atmospheres
piiatory loss co-operating to play the
i;gencies disturbing the liquid-equilibriut
uffeots the fact tliat, under normal circ
tropic phenomenon.
the ease of pot-plants with limited root-surfaces and exposed to
the limitation of supply of water and continued active ti-anspnrt
of slight meclianieal disturbances or other cxtrinsio
I of the tissues. Even if this be the case, however, it in no way
iinstances, deep depression of the petiole is not a normal nyoti-
II.—That when the p-imarij pethh
''stimuladon," its leaf hangi
during the early part of the t ^
is deeply depressed during the day
hose and pendulous; whereas when in the same position
I t is hardly necessary to discuss this <|uestion, seeing that, in pi
stances, the position of deep depression of tlie petiole, whether it aris
its ajipparance under precisely similar circumstances and is inducei
however, be pointed out that it is not true iu regard to plants grow
; hang loose and pendulous when petiolar depression has a
the ai-tio of D called " stimulant "
its grown under nornial circiimdiumally
or nocturnally, makes
by the same factors. It may,
under normal circumstances that
.en diurnally in consequence of
III.—That sudden exposure to absolute darknns, apart from any other disturling conditions,
is attended hy the occurrence of sudden movements in the leaves.
The following notes show the nature of tlie results of experiments in which plants, whose leaves
• lal diurnal position, were suddenly introduced into the absolute darkness of a photographic
3 of coloured glass atfnrding the
only I
om in which black velvet c
I uree of light under ordinary <ir
cPEKiMK^-T T I I I . - A f t e r an ex
1 of the various paits of the leo
; covered even the small windoi
of fi re minutes' duration
irred. Aft.er an exposn
I appreciable
of fifteen mil
the
s Vurlesuugcu ; Voii«uug, XXXVII, s. Tït
F
APPENDICES.
)giiisable. After
srmediate betwee
a the positions
iinry peti
nature
amount of pinnular elevation was
occupied a position more or less
positions. No perceptible alteratioi
entire course of the experiment.
EXFEHIMENT IX.—NO immediate effect foil
oi thirty njinutes liie pinnules occupied a posit!
and nocturual positions: at the close of an hot)
normal nocturnal position, but the pri
Eepeated experiments of a like
however sudden and complete it. be
sudden movements, aud that it is ii
even where it has acted di
and flevation of the pini
more rapidly iu plants exposed to a dry ati
that recovery of the diurnal position on
than in a dry atmosphere.
I u the case of ex
incidence of external infl
ixposure of thirty-two
)f the primary petiole i
itself 1
)wed transfer to the dar
3n almost iutermediato he
r the pinn® and pinnule
; remained elevated,
•quivocally showed that
I efficient fnctor in givin
tended by the occurrence
lutes the pinnules
)ul aud nocturnal
iurred throughout the
n. After an exposure
I the maximal diurnal
of light,
ng rise to the
le of deep petiolar depref
periods prolonged enough to secure maximal couvergence of the pi
They further »bowed that elevation of the pinnules i
losphere than in those exposed to
iuewed exposure to light >
nid one, and,
t rapidly :
•versely,
I humid
nature we have to deal with movements connected ^
vith the
s of the
determining fluctuations in the functional activities of the tissue
motor organs, but the fluctuations are of a negative not of a positive nature; tliey are dependent, not on
the incideuce, but on the removal of stimulation, aud the decrease in turgescence of the tissues of the motor
organs which directly determines the displacements of the various parts of the leaves is caused,
not by active contraction of the protoplasts of the tissue elements, but by the elastic recoil of the
cell-walls, which is no longer efficiently opposed owing to the decreased osmotic property of the cell-sap.
The movements aro of a slow and insensibly progressive character, as is the case with all movements arising
under similar circumstances. In all cases in which tlie occurrence of movements tending towards the
assumption of the nocturnal position in the leaves of Mimosa pudiea can be unequivocally traced to
alterations in protoplasmic functional activity acting alone, the displacement is invariably of a slow
gradually progressive character, and in all cases it is connected not with stimulation, but with depression
of protoplasmic activity. Sudden exposure to absolute darkness implies sudden deprivation of solar stimulation
of the protoplasts of the tissues, and with this a sudden depression of assimilatory activity ; but the
eSects of this do not manifest themselves suddenly, because assimilatory activity is only indirectly related
to the maintenance of maximal turgescence through the intervention of the osmotic properties which it
confers upon the cell-snp owing to the products which it adds to it. The deprivation of solar stimulation
places on arrest on the assimilatory addition of osmotic products to the cell-sap, but the actual loss iu
turgescence ultimately ensuing ou this will be regulated by the progi'sss of expenditure of the osmotic
products present at the time at which the arrest took place. The deprivation of tho conditions ser^uring
maiuteaauce of turgescence at a certain standard is sudden ; but the fall in turgescence
because it is connecttd with the gradual expenditure of a stock of pre-esistent unstable ma
tìL. SO,
iu the case of plants which are exposed to the influence of the vapour of chloroform ii
a humid
atmosphere, gradual progressive movements alone occur, because here again we have to deo
only with
depression and ultimate abolition of assimilatory activity leading to loss of osmotic capacity of the cell
sap, and through tliis to alterations iu the turgescence of the tissue-elements. Eut, whilst depression
of functional activity is iucapablo when acting alone to give rise to the occurrence of sudden movements,
it may serve to secure iheir occurreuce when it co-opcrates with othei' conditions favouring
losses in turgescence, but equally incapable of inducing the occurrence of sudden movements when acting
alone. The sudden introduction of a phmt into a desiccated atmosphere is, as a rule, followed merely
by very sk.w progressive movements of the pinnules, or, in cases where the root-supply of water is
very abundant, may be unattended by any movements whatevur; but sudden introduction into a chamber
eoutaiiiing both sulphui'io acid and chloroform is normally followed by the occurrence of sudden rapidly
executed movements, because here we have to deal not merely with conditions depressing functional
activity or giving rise to gi'eat increase iu tiauspiratoiy loss, but wi(h conditions implying the coincident
prcseuco of both these factors of decrease in turgescence. Are wo to suppose, as the ordinarily