THE CAUSES OE FLTJCTTJATIONS IN TUEGESCENCE
doGS not in itself tlctermme any approciablo dimmntion in the mass of contents
of the latter, but at the utmost a mere rearrangement of tliom. Active contraction wHI
give rise to increased prossnre in fluids contained within the substance of the contracting
protoplast, bat as these are relatively incompressible, the utmost that this is calculatcd
to give rise to is a more redistribution, o certain amoimt of fluid escaping from the
interior of the protoplasm and accumulating between it and the cell-ivall in plasmolytic
fashion. In so far as alterations in the mass of cell-contents are concerned, a protoplast
contracting within a cell is practically the parallel of a mass of muscle contracting within
a closed vessel of water. The distribution of the muscalar mass and of the surrounding
wator is altered, owing to the change of form occnrring in the former on contraction, but
the total bnlk of content of the vessel remains practically unaltered.
Mere protoplastic contraction being thus insnflicieiit in itself to give rise to diminished
tiirgescenoo in cells, we have next to consider how fat we have any reason to believe
that any redistribution of the cell-contents accompanying it may bo capable of doing
so. Were turgescence in cells necessarily dependent on the presence of fluids included
within tlie substance of the protoplasm, there would be good grounds for supposing that
any discharge of these from the latter might lead to diminished turgescence; but as
we know that turgescence is directly related to the products of protoplasmic activity
and not to protoplasm itself, and that it may be present in high degree apart from the
presence of any living protoplasm whatever, we have no grounds for regarding any mere
redistribulion of the cell-contents, apart from alterations in their osmotic properties, as
eflicient causes for alterations in cell-turgescenee.
H contraction of the protoplasts implied increased pressure on the exterior of the
cell-walls, or were necessarily accompanied by change in osmotic properties of the cellcontents,
it might well be accompanied by diminished turgescence; but as it certainly
cannot lead to the former, and as there is no evidence that it is necessarily associated
with the latter, we are justified in regarding it as incapable of afleoting ccll-tm-geseence
either directly or indirectly. The essential factors which determine the noi-mal fluctuations
in turgescence in vegetable cells are alterations in the osmotic properties ot their contents
and alterations in the conditions regulating general supply and loss of fluid or local
filtration; and it docs not appear that protoplastic contraction fer se is capable of
producing such changes.
Because conspicuous massive movements occur much more frequently in the organ,
isms of the higher animals than in those of the higher plants, it has been assumed that
the mechanism whereby they arc produced in the former must necessarily bo that which
causes them in the latter; but this is of course no matter of logical necessity. Movements
in an organism may be arrived at by two perfectly distinct paths—either by means
of alterations in form or alterations in bulk of its constituent elements ; in the case of
the higher animals the former, and in the case of the higher plants the latter, is that
which has been followed.
The lines which evolntion has pursued in the animal and vegetal series are divergent;
in the former contractile and, in association with this, irritable function; and in the latter
assimilatory function has been progressively highly specialised. The higher plants, owing
to their- great superficial extension and highly evolved assimilatory capacity, are enabled to
obtain sufficient nutritive materials from those supplies which are generally diffused throughout
their environment; consequently any special means for bringing them in condeuMd
and massive form into immediate relation to the organism are unnecessary. In the case
IN THE MOTOR OEGANS OP LEAVES. 5
of the higher animals, dependent as they are on supplies ot concentrated imtr-itive
materials, such moans are essential. The end to bo attained in both eases is a duo supply
of nutritive material to make good the constant waste to winch living protoplasm is
subject m the cxerciso of its functional propeiiies; in the one case this has been attained
by great specialisation of assimilatory function and great extension of surface in
t h e other by great specialisation of contractfle and irTitablo fanction. Even the most
indifierent protoplasm possesses a certam amount of contractile function; but in tracin»
the course of evolution along fhe animal and vegetal series of organisms we find that"
whflst in the former this has become more and more highly specialised, in the latter it
has remained in relative abeyance, wldle assimilateiy power has become predominant - so
that It would be just as surprising and anomalous to find any of the higher p l L ts
exhibiting phenomena nnplying the presence of liighly' specialised contractile apparatus
as to find any of the liigher animals capable ot supplying their nutritional i-enidi-ements
from purely inorganic sources.
Both on a jmori grounds and in the light of abundant positive evidence there is
thus good reason to believe that massive movements in the higher plants are not related
to the exercise of contractflo fimction, but to assimilatory function as afl'ectin» ' the
osmotic properties of the tissues, or to purely physical causes influencing geneml or
local supply and loss of fluid.
CHAPTER II.
• i E i u - g i l i i i g a s i k t i n g u i s h t i i f r o n t s i m p l e s a t u m l i o n.
I t is not diflicnlt to adduce evidence showing that turgescence is distinct from mere
saturation of tissues; but perhaps the most striking proof is that which is afforded by
the phenomena presenting themselves in connection with the exposure of many succulent
tuisues to the action of anssthctics. The demonstration is peculiarly striking in such
cases, because the materials on which the turgescence of the tissue depends arc unstable
in constitution and aro not accumulated in any considerable amount; so that any depression
of the functional activities to which they owe their origin is at once followed by
L t fa * / T f " °° " " " " -ccommodate the masses of it which escape, so
hat fice exudation takes place upon the sai-facc through the stomatic orifices. The fdl^w-
^ ^ « « - -
A.—Kalanohoe laciniata.
7 A leaf weighing 6-54 grammes was set in a chlorofor-m-chamber at
I p s o i f l a t l 1 r « " »' " ¡ " " t»
i t py a iJ, , " g art i 2l ^-d l0) rP..M . t Ìhh ee ^T VhaTd T bÌec' o"m' e somewhat flaccid and had acquired a