130 CüNNIKGIIAM ON FLUCTUATIONS IN i n i G E S C E N c E.
BoiTual oiroumStan009, nctod f u l l y as regards Iboir p r i m a r y petioles aad pianules, but showed h a r d l y any
appreciuble pinual converg^noe. It was at one« placed in a dark, moist chamber, wbieli was allowed
to remaiu closod until 8-20. When the chumbar was opened, the positiou of the various parta of
t h e leaves was fouud to be just the same ns it was whea they were enclosed ia it. The shoot was
now removed from the chamber, laiil on a fable in front of a window and covered by a ball-glass,
"Within a short period the ]>rimiiiy pctiolps gi-adually became partially elavatod, and the pinnules
assumed the normal diurnal pusiticm almost completely. Two hours later tlie petioles remained as
before, but the pinnules had assumed a positiou intermediate between the normal diurnal and
nocturnal ones. According to the ordinarily accepted theory of the causation of the movements in
l h a leaves of Mimosa piid'ca, wo are called ou in this instance to believe that the primary depression
of the petioles and elevation of the pinnules were dependent on stiiuulatiou and active contraction of
tlie protoplasts of the motor orgaus of the primary and t e r t i a r y piilvini incident on a factor—separation
f r om the axis—which failed to act as an a))preciable stiniuhint to the protoplasts of the secondary
p u l v i n i ; that this condition of stimulation and active contraction lasted continuously for nearly twn
hours whilst the shoot remained in the dark and deprived of any solar stimulus ; that it was then
replaced by a condition of relaxation on exposure to the influence of light ; and, finally, that continued
exposure to light acted as a stimulant to tlie contractile protoplasts of the tertiary pulvini, but failed
t o do so to those of the p r i m a r y ones. It is surely more rational to ©splain the sequence of phenomena
in the following fosh'ou. The primary depression of the petioles and elevation of the pinnules
were dependent on tha sudden disturbance of liquid equilibrium throughout the tissues, caused by the
sudden arrest of root-supply of watar and the active easape of liquid accompanying separation from
t h e axis. This depressivs distarbimoe was sufficient to give rise to considerable filtrative discharge of
liquid, and consequent loss in turgei^cenoe, in th^se sites in which special structural facilities for the
escapo of liquid f r om t h e interior of Cfli-oavities are present, and hence movements occurred connected
with sudden fall in tui'gescence in the inferior parenchyma of the primary pulvini and in the
superior parenchyma of the tertiary ones, wliilst no appreciable movements occuiTod in the pinnaj
because of the minor faciUties for rapid redistribution of liquid provided by the tissues of the seconda
r y pnlvinL Daring the period in wliioh the shoot was retained in the moist but dark chamber,
recovery of the diurnal position did not occar, not because there was not a stock of reserve water
within the wuter-con d u c t i n g system, or on aooouufc of active t r a n s p i r a t o r y loss, which was precluded by
the atmospheric humidity of tlie ohambir, but because the total absence of solar stimulation prevented
t h e protoplasts of tlie tissues f r om giving origin to the unstable assirailntory products on which the
osmotic capacity of the cell-sap, which is neccssary to induce full turgescenee o£ t h e tissue elements,
was absent. On subsequent exposure to sunlight, even under conditions implying no fresh supply
of liquid and p e m i t t i i i g of relatively free transpiratory loss, t h e rise in osmotic capacity in the cell-sap
was sidllcient to delertuine ai.-tive abso p t i o n of the reserve water in the water-conducting system, and
tlierefore t o determine a rise in the t urges oeiice of the pal via a r tissues leading to a resumption of the
diurnal position of the primary ]>etioles and the pinnules so long as enough reserve water remained
within the water-conductii)g system to more than counterbalance the coincident transjiitatory loss.
F i u i i l l y , when (as the result of continued transpiratory loss and assimilative decomposition of water) the
slock of reserve water became insufficient for this, a tendency towards the resumption of tlie nocturnal
position set in and manifested itself earlier and more conspicuously in the pinnules t h a n in the primary
petioles, because the action of local loss of turgesoence in the tissues of the primary pulvini was more
or less discounted by the coincident diminution iu distal leverage attending diminished turgescence in
t h e himiuar portions of the leaves.
The effects of a normal depression of assimilatory activity, or in other words of a normal
decrease in tlie osmotic capacity of the pulvinar tissues in giving rise to a greater liability to the
occuirence of movements, or as it would be commonly described to " increased i r r i t a b i l i t y , " is very
s t r i k i n g l y demonstrated in connection with experiments, like the following, in which the tips oi uxea
a t e g e n t l y amputated without acy mechanical disturbance of the plants ;—
Exi'KBImest ll.—Jti>ie 'dnl. Both soil ami air viry humid—M 8 .\.m, the leaves were in full diurnal
position. Amputation of the tips of axes was followed m«rely by the exudation of a great drop of
liquid from the cut suiface. At 7 f.m. the leaves were in full noeturnal position. Amputation of
Al'PENDICES. 151
t h e tips of axes was followed by no conspicuous exudation, but by centripetal propagation of
movements of petiolar depression to many leaves along the course of tlie i n j u r e d axis.
ExPEinME>-T III.—August 20i/i. Thru had been heamj shoimrs in the morning, so thai the soil was
saturated, hut iuhsciittenlly conlinuous radiant sunshine had prof ailed. 1 p.m.—The plants were not exposed
t o direct sunshine and the leaves «ere iu maximal diurnal position. Amputation of the tips of axes
led to local exudation of liquid, but wns unattended by the occurrence of any petiolar movements.
(i-30 P.M.—Ihe leaves were in full nocturnal position. Amputation of the tips of axes was followed by
extensively propagated movements of deepest petiolar depression along the course of the i n j u r e d shoot.
I n compnriug the riisults of experiments carried out respectively in the morning and evening it
cannot, of course, be maintained that all the difTerences wliieh are present—that all the pbeuomena of
increased " i r r i t a b i l i t y " in t h e evening—are to bo credited to t h e coincident depression in assimilatory activity
a l o n e ; for, as a rule, the conditions m tlie evening are much more favourable to rapid transpiratory loss
t h a n they are in the morning. During periods of continuous settled weather diurnal atmospheric
h u m i d i t y attains i t s minimum in the afternoon and evening, whilst iu t h e morning it is still relatively
high. This is s h o ^ n by the figures in the following table of averages, derived f r om a series of weekly
observations for the yeais 189^-93 with which my f i i e u d Mr. 0. L i t t l e has kindly f u r n i s h e d me :—
Average aimoipkeric hvmidiiy ai varic-vs Hmis of day. lW=sutuyatioii.
1892.
J a n \ i a ry
F e b r u o ry
March
April
May
J u n e
J u ly
August
September
October
November
December
Annual averages
1893.
J a n u a ry
F e b r u a ry
March]
April
May
J u n e
J u ly
August
October
November
Documbor
Annual averngos
6 A.M. 8 A.M. 1 0 A.M. 4 p,si. 10 P.M,
9 0 - 2 8 5 7 C2-5 4 0 - 5 7 8 - 2 5
8 4 -5 7 1 - 4 4 8 -6 3 5 - 0 7 4 - 8
8 S 0 7 5 - 6 4 8 - 7 3 3 1 - 0 7 1 - 7 5
8 7 -8 7 7 - 7 5 6 3 -0 5 4 - 0 8 1 0
8 9 - 0 7 9 -2 7 0 - 6 5 9 - 2 8 5 - 2
9 2 0 8 2 - 2 5 7 3 - 2 5 7 3 - 7 5 9 0 0
9 6 0 9 0 - 2 5 8 6 - 7 5 8 3 - 0 9 2 -5
9 I ' 8 8 9 - 0 8 0 - 4 7 8 - 4 9 1 - 4
9 5 - 7 5 8 5 - 5 7 7 - 2 5 7 7 - 7 5 9 2 - 5
9 S ' 2 8 2 -6 7 2 - 6 C5-6 9 1 - 4
8 7 7 7 7 - 7 5 5 9 -5 4 7 - 0 9 2 -0
8G-25 7 9 - 5 5 3 25 3 5 - 7 5 8 8 - 2 5
9 0 -6 8 1 -3 6 6 - 3 5 6 -9 8 5 - 7 5
C A.M. 8 AM. 1 0 A.M. 4 P.M. 1 0 P.M.
9 3 ' 0 9 0 0 6 3 -0 4 0 - 6 8 3 - I
9 4 - 7 5 8 7 -5 7 1 - 7 5 6 3 -0 9 1 0
9 4 25 FC8-25 6 0 -0 5 4 -5 8 3 - 2 5
9 1 - 2 5 8 0 - 7 5 6 4 - 7 5 5 4 0 85-2Ö
8 9 ' 2 8 1 - 0 6 9 - 2 0 5 9 -8 8 1 - 40
9 2 - 7 5 8 6 - 3 5 8 4 - 50 8 2 - 7 5 8 9 - 2 5
9 3 - 8 8 8 - 0 8 4 - 4 0 8 2 - 4 0 8 9 0
9 4 - 0 8 7 - 5 &1-0 7 7 - 0 9 0 -5
9 5 ' 2 5 9 0 - 2 5 8 5 - 2 5 8 2 - 7 5 B'2-75
9 2 -8 8 4 - 0 7 8 - 2 5 7 3 - 2 5 9 4 -0
8 5 -5 7 6 - 7 5 6 2 -0 Ö 7 '5 9 2 0
9 4 - 2 5 8 2 - 25 6 4 - 2 5 5 0 - 2 5 9 1 - 2 5
9 2 - 4 . 8 5 - 2 7 2 - 8 6 4 -7 88-Ü