Cuap. X. MEANS OF MOVEMENT. 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 irri- 
tated 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, 
