208 DROSERA ROTUNDIFOLIA. (Cuap. X. 
tension, and that they are elastic to an extraordinary degree ; 
tor otherwise their contraction could not cause the tentacles 
often to sweep through an angle of above 180°. Professor 
Cohn, in his interesting paper* on the movements of the 
stamens of certain Composit, states that these organs, when 
dead, are as elastic as threads of india-rubber, and are then 
only half as long as they were when alive. He believes 
that the living protoplasm 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 homo- 
geneous, 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, though 
* ¢ Abhand. der Schles. Gesell. fiir given in the ‘Annals and Mag. of 
vaterl, Cultur, 1861, Heft i, An Nat. Hist.’ 3rd series, 1863, vol, ix. 
excellent abstract of this paper is pp. 188-197. 
