Cuar. X.J NATURE OF THE MOTOR IMPULSE. 209 
rejected by most others, is that the whole cell, including the 
walls, actively contracts. If the walls are composed solely 
of non-nitrogenous cellulose, this view is highly improbable ; 
but it can hardly be doubted that they must be permeated 
by proteid matter, at least whilst they are growing. Nor 
does there seem any inherent improbability in the cell-walls 
of Drosera contracting, considering their high state of organi- 
sation ; as shown in the case of the glands by their power of 
absorption and secretion, and by being exquisitely sensitive 
so as to be affected by the pressure of the most minute 
particles. The cell-walls of the pedicels also allow various 
impulses to pass through them, inducing movement, increased 
secretion and aggregation. On the whole the belief that the 
walls of certain cells contract, some of their contained fluid 
being at the same time forced outwards, perhaps accords best 
with the observed facts. If this view is rejected, the next 
most probable one is that the fluid contents of the cells shrink, 
owing to a change in their molecular state, with the con- 
sequent closing in of the walls. Anyhow, the movement can 
hardly be attributed to the elasticity of the walls, together 
with a previous state of tension.* 
With respect to the nature of the motor impulse which is 
transmitted from the glands down the pedicels and across 
the disc, it seems not improbable that it is closely allied to 
that influence which causes the protoplasm within the cells 
of the glands and tentacles to aggregate. We have seen that 
both forces originate in and proceed from the glands within 
a few seconds of the same time, and are excited by the same 
causes. The aggregation of the protoplasm lasts almost as 
long as the tentacles remain inflected, even though this be 
for more than a week; but the protoplasm is redissolved at 
the bending place shortly before the tentacles re-expand, 
marks on the lower surface and fuund 
* [See Gardiner’s interesting paper 
“On the Contractility of the Proto- 
plasm of Plant Cells ”(¢ Proc. R. Soc.’ 
Nov. 24, 1887, vol. xliii.), in which he 
gives evidence tending to show that 
the curvature of the tentacles of 
Drosera is brought about by contrac- 
tion of the protoplasm. 
Batalin (‘Flora,’ 1877) experi- 
mented on the curvature of the 
tentacles as well as on the bending 
of the blade of the leaf. He made 
that when the curvature takes place, 
the distance between the marks on 
what becomes the convex surface of 
the leaf or tentacle increases. When 
the leaf opens, or the tentacle 
straightens, the distance between the 
marks does not return to what it was 
at first, and this permanent increase 
shows that the curvature is connected 
with actual growth.—F, D.] 
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