258 DROSERA ROTUNDIFOLIA. Cuar. X 
though 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 organisa- 
tion; 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 aggrega- 
tion. 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 consequent 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 pedi- 
cels 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 ten- 
tacles 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 
