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24 THE CAUSES OF FLUCTUAriONS IN TURGESCENCE
corolla, the margms gradually assumed aa orange tiat, and on the following day the
flower, although liardly showing any signs of collapsc, was of a uniform hrowiush
orange throughout.
Expcrment JX.—A flower of scarlet Hilnsctcs in a chloroform-chamber very rapidly
collapsed, and at the same time assumed a deep maroon red colour. Immersion of the
discoloured petals respectively in dilute acetic acid and in 10 per cent, solution of caustic
potash caused them, in the former instance, again to become scarlet; and, in the latter,
to turn first dull blue, then dull green, and finally ochreoiis.
Experiment X.—Two flowers of Ipomcea hcdcracea were placed in a chloroformchamber.
The deep blue portions of the corollas almost immediately began to acquire
a violet, and the pale ruse of the red parts an ochreons tint. The violet of the blue
areas gradually reddened and, at the same time, the texture visibly became moistened.
The corollas ultimately collapsed, the originally red area being now ochreons and
the originally blue ones dull red.
Experiment XI.—A flower of Ipnmcea hederacea was set in a moist chloroform-chamber
at 10-31 A.M. The blue area of the corolla gradually becamc first violet and then
dull rod, and at the same time slowly collapsed.
Erperiinent XII.—A flower of Ipomcea hcilatacca was set in a moist ammoniachambev.
After three minutes' exposure it had become of a vivid peacock green, -which
gradually faded to a pale ochre.
The changes in colour in the flowers of Ipomcea hederacea under the influence of
cliloroform are just the reverse of those -which normally take place during the expansion,
but are the same as those attending the withering of the corollas. Whilst in bud the
areas which, during full expansion, are reddish have an ocljreous, and those which
are deep blue a red colour; and in the fading and faded corollas of the afternoon
and night a rovei-sion to the bud colouring takes place. When the dull red faded
corollas are treated with acids they become vivid rose colour; and, when treated with
alkalis, vivid blue and green, passing on into pale yellow. When the flowers are
in bud and in the faded condition, the cell-sap thus evidently contains a relative excess
of acid constituents; whilst, when the flower expands under favourable conditions of light,
and specially of temperature, these acids are partially neutralised by the manufactm-e of
alkaline products. Stimulation of the functional activities of the tissues in this case gives
rise to effects similar to those accompanying it in tissues containing chlorophyll, and
precisely the reverse of those occurring in the case of tissues in which the cell-sap is
noiinally red during their fullest development. The brilliant scarlet of the fully expanded
corollas of scarlet vaiicties of Hibiscus rosa-sinen&is is replaced in the bud and in the
fading condition by a dull red colour, which, especially in the latter case, is very much
of the same character as that developed in the expanded corollas under the influence of
chlorofoi-m. In the case of chlorophyll-containing tissues, and in those in wliich the cellsap
is of a blue colour when they are most highly developed, stiumlation of protoplasmic
acri-s-ity appears to lead to relative alkalinity; and depression or abolition of protoplasmic
activity to relative acidity; whilst, in the case of tissues containing red cell-sap, precisely
the reverse is the case. The essential constituents of both red and blue colouring matters
IN THE MOTOR ORGANS OF LEAVES. 25
appear to be the same, the tint being determined by the relative acidity or alkalinity
of the medium. Hence blue flowers usually present a more or less pm-plish or reddish
tinge in natural fading and when under the influence of chloroform; whilst red ones,
on the contrary, lose their brilliancy and may even become almost colourless (Hke those
of Erythrina stricta) under similar circumstances. The colour in Erytlmna stricta is evidently
related to intense acidity of the mediimi; for even perfectly neutral media reduce it very
much, just as strong alkalis act on other red tissues; while the alcoholic extract demands
an excessive addition of acid ere it reacquires a scarlet tint. Some blue flowers, such as
those of the blue variety of Ciitoria Ternatea, present an exception to the rule enunciated
above, as they retain an intense blue coloiu- during normal fading and exposui-e to
chloroform, and they yield brilliant pure blue infusions and extracts on boiling and
immersion in alcohol. This is not dependent on any peculiarity in the essential constituents
of the colour, for the addition of acids to the blue 'extracts or infusions at once
causes them to assume a beautiful red colour; but must apparently be due to the cell-sap
normally containing a relative excess of fixed alkaline constituents—an assumption
which is favoured by the very feeble acidity which the freshly expressed sap presents.
The extremely fugitive nature of the alkaline constituents in some other cases is most
strikingly exemplified in cases where flowers of Ipomoea hederacea are killed by means of
exposure to low temperatures, as the following experiment shows:—
Experiment XIII.—A fully expanded and normally coloured flower was enclosed
in a metal box, and the latter was then buried in a mixture of pounded ice and salt,
where it remained for an hour and a half. At tlie close of this period the flower
remained fully expanded and retained its original colouring, but was frozen and rigid.
On removal from the box immediate collapse occurred, and the colours of the normally
blue and red areas at once changed, the former becoming violet and the latter
ochreoua. Tlie white coloured portion at the base of the tube retained its colour
somewhat longer, and then, like the red ones, became ochreous, the blue portions having
meantime passed on from purple to dull red.
Immersion of flowers of the same species in boiling water is followed immediately
by total collapse and similar changes in colour, but the results in this case are not so
strikmg, as they are not so conclusively ascribable to mere cessation of protoplasmic
activity as where they follow exposure to cold. The absence of collapse and the retention
of the normal coloui- in the latter case, so long as the tissues remain frozen, must
apparently be due to the cell-sap being congealed so rapidly that no appreciable escape
of liquid or discharge or decomposition of the fugitive alkaline or acid constituents
present in it have time to occur. The process of rapid congelation not only arrests the
manufacture of the products of protoplasmic activity on which the turgescence and
colour of the tissues depend, but it for the time being retains those which are present
in the sap at the moment at which congelation occurs. On the tissue thawing, an
immediate loss of turgescence occurs, and this is accompanied by the escape or decomposition
of the products of certain constituents of the cell-sap to which its normal
colour is due. It would be hard to find a more striking instance of the coincidence of
loss of turgescence with alterations in the chemical constitution of cell-sap.
I t is only where the coloui-s of the tissues depend on the presence of dissolved
pigments, the tints of which are determined by the presence of fugitive acid or alkaline
substances, that they serve as satisfactory indices to the occurrence of chemical changes
ANN. ROY. BOT. GARD. CALCUTTA VOL. Y I .