mi
22 THE CAUSES OF FLUCTUATIONS IN TURGESCE.N'CE
Experiment V.—Two leaves of Kalanchoe with iuteusely acid sap were taken at
10-15 A.M. One, a, weighed 28-7 grammes; the other, h, 28-58 grammes. Both were
then set with the bases of thoir petioles immersed in water, and a was exposed to direct
sunsiiitie and' h to absolute darkness for three hours and a half. At the close of this
period, a weighed only 27'3 gi-ammes, and the acidity, and especially the permanent
acidity, of its juice was voiy greatly diminished in intensity; while h weighed 27'87
grammes and jnelded fluid of excessively acid reaction. On the following morning the
acidity of the sap in both cases was alike and intense. I'he leaf b was now enclosed
in a moist chambcr and exposed for three hours in absolute darkness to a temperat\ire
of 88-7 in order to detei-mine whether the effects follo%ving exposure to sunshine
were in any appreciable degree detennined by heat as distinct from light; but the
acidity of the sap remained undiminished at the end of the experiment.
In this case the stimulant ultimately loading to a diminution in the acidity of
the cell-sap is evidently light, but in other cases heat comes j^rominently into play in
producing similar results. For example, whenever the temperatm-e remains beneath a
certain limit the flowers of Ipomoea hederacea, however brilliant the sunlight be, never
attain the intense, dusky blue normal to them T\'hon in the expanded condition, but
retain more or less of the red tint proper to the buds—a phenomenon which, as we
shall presently see, is due to a relative excess of acid constituents in the cell-sap. Ilere
temperature is the dotei-minant of decrease in acidity, just as in other cases we find that
it is the essential determinant of the increase in turgidity of certain masses of tissue
on which the expansion of flowers such as those of Portulaca graniijlora is dependent.
The flowers of Portulaca do not unfold in the brightest sunshine until they have
attained a temperature of 70"" to SOT.; and, if only this be provided, expansion takes
place in total darkness just in proportion to the rise in temperature. Both heat
and light are cleai-ly capable of determining chemical alterations in tlie nature of the
cell-sap and increase in the turgescence of masses of tissue. According to Sachs'
theory of the causation of turgescence, in order to account for the phenomena we must
assume that in some cases the factors act on the physical properties of the protoplasm,
and in others on the chemical nature of the cell-sap; or, in other words, that in some
cases they affect the structure and in others the function of the protoplasm. J^ut surely
it is more reasonable to assume that both chromatic and motor effects are due to
stimulation of the latter only. Such stimulation may well give rise to the formation
of products differing from one another in different instances, in some characterised
by their reaction and in others by their osmotic properties, and accordingly ultimately
detei-mniing changes of colour in the one case and movements related to altered turgescence
in the other case.
In some cases stimulation of functional activity, whether photic or tliermic, leads
to decrease and in others to increase in the acidity of the cell-sap and to corresponding
changea in the tint of colouring matters which are dissolved in it, the intensity
of blue and green colours being related to relative alkalinity and that of red
ones to relative acidity. That this is the case is shown by the results of tlio
following experiments:—
Fxpei-iment J.—The petals of a flower of Erythrina striata, which are of a brilliant
scarlet colour, exposed in a chloroform-chamber almost immediately became of a
O THE MOTOB OKGANS OF LEAVES. 23
permanent, pale, dull, brownish pink tint. The flower was now transfen-ed to a
carbonic acid chamber in which the petals gradually reddened, and in the course of
twenty-four hours they had regained a vivid scarlet colour.
Experiment //.—Petals of the same Erythrina, when innnersed in absolute alcohol,
were at once bleached to a very pale pink, the alcohol at the same time acquiring
a very pale, reddish topaz tint, which rapidly 3'eddened in a carbonic acid chamber
and became vivid scarlet on the addition of a few drops of glacial acetic acid.
Alternate additions of solutions of caustic potash and glacial acetic acid to alcoholic
extract which has become scarlet owing to prolonged exposure in a carbonic acid
chauiber, secure alternating discharge and reformation of the colour.
Experiment III.—A flower of a scarlet variety of Jlibiscus rom-sinensis was set in a
cliloroform-chamber. The colour very rapidly began to become dulled, and within an
hour was of a dull maroon red, the corolla at the same time showing the initial stage
of collapse. The chloroform was now removed from the chamber and a vessel of
glacial acetic acid substituted for it. Collapse of the corolla continued to advance
steadily to completion, but at the same time its colour gradually revived and ultimately
became once moi-c vivid scarlet.
Experiment IV.—k similar flower of Hibiscus, momentarily immersed in boiling
water, collapsed at once, the colour at the same time becoming purplish. The water
also acquired a purplish hue, due to extraction of pigment and partial bleaching of
the corolla. The purplish infusion was rendered bright red by the addition
acids. of
Experiment V.—A similar flower placed in a chloroform chamber gradually underwent
the same changes as that in Experiment I I I.
When the colour- had become of a deep maroon red, the chloroform was removed
and a vessel of fuming nitric acid substituted for it. Restoration of the coloui- began
visibly almost at once, and a vivid scarlet was gradually re-established.
Expm-im&it VI.—A similar flower was enclosed in a metal bos and buried in a
mixture of ice and salt. After an hour and a half of exposui-e it was found to be
stiffly frozen aird of a dull red coloui-. It was now placed in a simple hermeticalJy
closed chamber, and the colom- soon passed on to the same deep maroon tmt
which is developed under exposure to chloroform, flaccidity and collapse also advancing
rapidly. On the following day it was quite flaccid and deep maroon. A vessel of
glacial acetic acid was now introduced mto the chamber, and twenty-four hours later
the corolla was once more vivid scarlet.
Experiment T//.—Petals of scarlet Hibiscus immersed in absolute alcohol became at
onco deep piu-ple and yielded a neuti-al extract of a reddish topaz colour. Treated
with acids, this extract became vivid red; and with alkalis dull green, iDassing on to
orange yellow.
Experiment VIIL-A scarlet Uihisem ilower was set in a moist ammonia-chamber
l u r p h s h black spotting of the corolla began to appear within a minute and extended
rapidly. As the blackening extended inwards from the periphery to the centre of tl.e