CHAP. 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 cell* 

 contract, the rest of the tentacle remaining straight. 



A third view maintained by some physiologist^ 



