12 THE CAUSES OF FLUCTUATIO.NS IN TUEGESCENCE
Experiment I I.—A. leaf of Kalmichoc, -n-eighing 11'6 grammes^ was immersed for half
a minute in water at a teinperatm-o of 90°a, and then, aftei- being gently dried, set in
a liermetically closed chamber. Visible exudation began to appear on the surface within
five minutes, and -within four hours it had assumed a yellowisli olive colour and weighed
only 10-1 grammes. On the following morning it had lost 0-4 grammes more, giving a
total loss of l-9f.c. of fluid, or 16 per cent, of total weight.
Just as in the case of leaves treated by exposure to chloroform, the amount of loss
of fluid taking place from the tissues varies according to the time of year, presumably
in relation to the age of the leaf and the area presented by the intercellular spaces, or
to the precise nature of the osmotic products present in the cell-sap at different seasons.
For example, whilst in the two previous experiments, -which were conducteJ in January,
when the loaves are in a dormant condition as regards growth, the losses in weigiit
amounted respectively to 19'3 and 16-3 per cent, of tlio total, whilst in one carried out
in the end of May the total loss amounted to only 4'01 per eont.
Experiment Ill.—k. loaf of Ciissia simatrana with eleven pairs of pinnae was taken,
and the ecutrally situated pair and the corresponding portion of tlie rachis were dipped
into boiling water. boiled pinnfe became flaccid at once and dropped vertically
downwards from the petiole, with their upper surface looking directly outwards. The
base of the petiole was now freshly divided under water, and the leaf, along wáth a check
one, set to stand in a bottle of water in the open laboratoiy The boiled pinnic had at
once assumed a yellowish olive tint and presently became distinctly yellow, the colour
being quito distinct from that following prolonged exposure to chloroform. A certain
amount of tendency towards the assumption of the normal nocturnal position manifested
itself in the pair of pinnaj immediately beyond the boiled portion of the petiole, but
this had completely disappeared within the course of three hours. On the following day
the boiled portions of the leaf were yellowish-brown and dry, whilst the proximal and
distal portions were green and turgid. The pinnte of the distal portion were, however,
moro or less in the nocturnal position, this being, no doubt, duo to the fact that, whilst
the conduction of water through the wood remained uuimpaii-ed, the dead superficial
tissues of the boiled portions of the leaf presented a site of abnormally excessive
evaporative loss, as indicated by their dry condition.
Experiment IV.—A leaf of Cassia sumatrana, like the preceding one, was taken and
the fourth and fifth pans of pinnte with the corresponding portion of the rachis were
dipped into boiling water. Immediate and total depression of those pinnai occurred, and
was soon followed by a partial assumption of the nocturnal ¡josition in the sixth pair.
The base of the petiole was now freshly divided under water and luted into a water-bottle
in a hermetically seaJed chamber. The sLxth pair of pinna; rapidly resumed the fully
expanded condition, and yellowing of the fifth and sixth pairs and of the corresponding
portion of the rachis soon manifested themselves, the surface of the rachis at the same
time becoming studded by an exudation of drops of fluid. On the following day the
boiled pinnfe were quite flaccid, moist and yellowish-brown, and the corrcspondinNportion
of the racln's was covered by large drops of brownish fluid, while all the rest
of the leaf was turgid, bright green and fuUy expanded. It was now removed from the
chamber and set in the open laboratory, and, in a short time, the drops of exudation
disappeared from the boiled portion of the rachis and simultaneously the distal intact
IN THE MOTOR OllGANS OF LEAVES. 13
pinncc began to show rotation and depression, whilst the proximal ones retained the fully
developed diunial position unaltered. The fact that boiling the tissues in such cases
leaves theii- conducting power for water unimpaii-ed, whilst reducing their retentive power,
could hardly be more clearly demonstrated than it is in the results of this experiment
by the phenomena of exudation in the boiled areas and full expansion of the distal intact
ones whilst the leaf remained in a moist atmosphere, and of disappearance of exudation
and partial assumption of the nocturnal position by the same pinnas when the leaf was
exposed to free evaporative loss. On the following day the level of the water ia the
bottle had sunk so much that only the tip of the petiole remained immersed. The boiled
portions of the leaf wore dry and brown, the others were green and turgid, but somewhat
inclined towards the nocturnal position. The leaf was now returned to a hcruiotically
closed chamber, and on the following day exudation had reajjpeared on the boiled portion
of the rachis and the intact pmn« were once more in a condition of full expansion.
Experiment V.—Two leaves of Cassia sumatrana were taken, the one, a, having seven
paii-s of pinna3, the other, which was somewhat larger, only six and a half pan-s. The
thii-d pair of pinnai and the corresponding portion of the rachis of a were immersed in
boiling water, the treatment causing almost immediate browning and flaccidity of the
immersed tissues, and temporary drooping, with more or less assumption of the nocturnal
position in the pinnaj beyond the point of immersion. The bases of the petioles of both
leaves were now freshly divided under water and then securely luted into water-bottles,
the levels of the water m the latter being at the same time accurately marked. The
leaves stood side by side in the open laboratoiy until the following day, when both
were found to be alike turgid, save the boiled portions of a, wliich, as usual with
exposed portions of tissue after similar treatment, were brown, diy, and drooping. The
amount of water which had been absorbed during the interval in both cases was 3c.c.
Experiment VI.—A large leaf of Cassia alata was taken, and all but the five distal
pairs of pinnse were cut off. The lower part of the petiole was then plunged into boiling
water for half a minute, and, its extremity having been cut off subaqueously, was luted
into a water-bottle. The apparatus was then set in a sealed chamber containing a vessel
of strong sulphuric acid. The level of the water in the bottle began at once to dcscend
visibly. On the following day that part of the boiled portion of the petiole which was
above tlie water was of a brown colour and coated with cbops of brown fluid. The
pinnae at the same time were fully expanded, turgid, bright green and, as usual wlien
saturated with fluid, studded marginally with drops of clear liquid. The water in the
bottle had meantime sunk • very considerably. On the two following days the pinnae
retained their greenness and turgidity, and at the close of the experiment the quantity
of water which had been absorbed amounted to ISc.c.
Experiment VII.—K large leaf of Cassia alata was taken, the basal paii- of pinnai
removed, and the lower four and a half inches of the rachis immersed in boiling
water for two minutes. The end of the petiole was then freslily cut off under water,
and the leaf sot in an open water-bottle and fixed, so that tho lower part only of the
boiled portion of tho petiole was immersed. Visible depression of the level of the
water set in at once, and in the course of two hours a loss of 12c.c. had occurred.
On the following morning an additional loss of SSc.c. was registered, giving a total