314 
NATURE 
[JANUARY 31, 1907 
responses given by metal bars. In these experiments 
the work done on the bar, generally by torsion, greatly 
exceeded the output of energy in the electrical and 
other response produced. There is no liberation of 
stored potential energy in such a case, therefore there 
is really no similarity with the mechanism of the 
liviag cell, though molecular change no doubt occurs 
in the protoplasm as it does in the metal wire. 
Just as we hold that Dr. Bose has transferred from 
his physical experiments a conception of biological 
stimulation which is inadmissible for either animal or 
vegetable cells, so it seems to us that his conception 
of contraction is derived only from the activity of 
animal muscles, and is inadmissible for the mechanical 
response of plant cells. There is really no evidence 
that these two phenomena are of quite the same order 
and both due to active contraction of the living part 
of the cell, though an a priori philosophical outlook 
has led many to assume it. 
When the irritable stamens of Centaurea 
touched they shorten, even to one-third of their length, 
which diminution is accompanied by an extrusion of 
a corresponding amount of cell sap from the cells 
into the intercellular spaces, and by comparative 
flaccidity of the cells. 
Now. the vegetable cell, unlike the muscle cell, is 
at its maximum rigidity when at rest, being distended 
by the osmotic force of molecules dissolved in its sap. 
These molecules are kept in by the protoplasmic 
lining of the cell, which is impermeable by them 
though freely permeable by water. The tenacious and 
elastic cell-wall, itself freely permeable to everything, 
is able, owing to its tenacity, to protect the proto- 
plasm from being ruptured by the osmotic pressure, 
which reaches several atmospheres. 
Whether one holds the view that the shrinkage 
which occurs on stimulation has, as its antecedent 
stage, decomposition of some of the osmotic molecules, 
or sudden permeability of the protoplasm, the contrac- 
tion itself cannot be attributed to active contraction 
of the living part, but must be due to the forceful 
elastic contractile recovery of the dead cell-wall, now 
no longer distended through osmotic force. It is in- 
credible that the stimulated protoplasm, so watery in 
texture, can contract actively against an extending 
force of several atmospheres and actively expel cell- 
sap. Unlike muscle, the ‘‘contracted”’’ plant cell is 
flaccid, and the protoplast does its mechanical work 
while recovering from contraction, in again extending 
‘its wall ready to react to fresh stimulation. This 
corresponds to the relaxation time of a muscle, so 
that the two machines are quite different in their 
are 
phases. 
Further, another fundamental difference lies in this, 
that ‘a muscle does not really contract in volume when 
stimulated; it merely alters its shape, becoming 
shorter and broader, a special property exhibited by 
a number of non-living peculiarly organised structures, 
india-rubber strips, for example. The plant cell, on 
the contrary, really contracts in volume; whether it 
alters its shape depends upon the relative extensibility 
of the different walls. Again, this contractility of 
plant cells is inherent in the very organisation of the 
NO. 1944, VOL. 75] 
j cell, and is found in all. primitive types and in all 
young cells, and is not a specially evolved mechanism 
like the contracting muscle. fibre. It is finally interest- 
ing to note that it has not been really proved that 
heat production is associated with the contraction of 
plant cells rather than with the subsequent expansion 
when work has to be done by the protoplast. 
Dr. Bose’s conception of growth is more elusive and 
still more isolated. Growth, the indirect remote re- 
sponse to stimulation, is due to that part of the 
energy of a stimulus not used in direct response. 
This energy is held to be communicated hydraulically 
to the growing point as pulsations, and of these 
pulsations graphic records are given. Stimuli applied 
directly to the growing region must, of course, cause 
contraction, t.e. retardation of growth, as their direct 
response; therefore the pulsations of the growing 
point are attributed, as indirect responses, mainly to 
excitatory reactions occurring below the zone of 
growth. 
Dr. Bose’s book abounds in experimental evidence 
on all points, a feature of the greatest merit, yet we 
must say that many of the fundamental experi- 
ments are not nearly critical enough. For example, 
one reads continually of the striking effect of thermal 
stimuli: these are produced by the electric heating 
of a platinum-wire-frame which surrounds the living 
stem; when a succession of stimuli is wanted it is 
produced by passing and cutting off the current 
alternately. In relation to this treatment we are 
given no idea of the temperature that the wire or the 
plant attains, or of how far the temperature of the 
plant actually oscillates under this alternately ‘hot 
and cold environment. The effects produced in this 
way are very extraordinary—longitudinal contraction 
of stems, styles, and other radial organs, stimulation 
of Mimosa pulvini, &c.—but there is no attempt to 
the transition from such effects to those of 
high temperatures which are kept 
trace 
surrounding: 
uniform. 
The reader rather distrusts the author’s views on 
thermal effects on finding him propose seriously to 
examine (chapter xliv.) the effect upon growing parts 
of ‘thermal radiation’’ apart from the effect of the 
actual temperature of the part. This distinction is 
surely confusion of thought, and the differences re- 
corded are no doubt due to actual difference of 
temperature, for the method of experiment is quite 
fallacious. It is, indeed, supposed that a plant sur- 
rounded with a hot radiating platinum spiral, the 
whole being enclosed in an experimental chamber, 
will be at the same temperature when there is a heat- 
proof screen between the plant and the radiating 
spiral and when this is removed, and this just because 
a thermometer somewhere in the general air of the 
chamber keeps a uniform constant temperature all 
the time! ’ 
The apparatus and the experimental methods 
employed show great ingenuity and a praiseworthy 
simple directness of attack which, however, occasion- 
ally passes into naiveté. One feels that valuable 
results are to be got with the delicate optical lever, 
the kunchangraph, the balanced crescograph, the 
