* ‘Abhand. der Schles.  Gesell. fr vaterl.  Cultur,’ 1861, Heft i.  An excellent abstract of this paper is given in the ’Annals and Mag. of Nat.  Hist.’ 3rd series, 1863, vol. xi. pp. 188-197. [page 257]

within their cells is ordinarily in a state of expansion, but is paralysed by irritation, or may be said to suffer temporary death; the elasticity of the cell-walls then coming into play, and causing the contraction of the stamens.  Now the cells on the upper or concave side of the bending part of the tentacles of Drosera do not appear to be in a state of tension, nor to be highly elastic; for when a leaf is suddenly killed, or dies slowly, it is not the upper but the lower sides of the tentacles which contract from elasticity.  We may, therefore, conclude that their movements cannot be accounted for by the inherent elasticity of certain cells, opposed as long as they are alive and not irritated by the expanded state of their contents.

A somewhat different view has been advanced by other physiologists—­namely that the protoplasm, when irritated, contracts like the soft sarcode of the muscles of animals.  In Drosera the fluid within the cells of the tentacles at the bending place appears under the microscope thin and homogeneous, and after aggregation consists of small, soft masses of matter, undergoing incessant changes of form and floating in almost colourless fluid.  These masses are completely redissolved when the tentacles re-expand.  Now it seems scarcely possible that such matter should have any direct mechanical power; but if through some molecular change it were to occupy less space than it did before, no doubt the cell-walls would close up and contract.  But in this case it might be expected that the walls would exhibit wrinkles, and none could ever be seen.  Moreover, the contents of all the cells seem to be of exactly the same nature, both before and after aggregation; and yet only a few of the basal cells contract, the rest of the tentacle remaining straight.

A third view maintained by some physiologists, [page 258] 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 organisation; 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 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.