256 DKOSERA ROTUNDIFOLIA. Chap. X. 



the bending tentacle. But it does not follow from 

 these observations that the cells on the convex side 

 become filled with more fluid during the act of in- 

 flection than they contained before ; for fluid may all 

 the time be passing into the disc or into the glands 

 which then secrete freely. 



The bending of the tentacles, when leaves are im- 

 mersed in a dense fluid, and their subsequent re- 

 expansion in a less dense fluid, show that the passage 

 of fluid from or into the celJs can cause movements 

 like the natural ones. But the inflection thus caused 

 is often irregular^ the exterior tentacles being some- 

 times spirally curved. Other unnatural movements 

 are likewise caused by the application of dense fluids, 

 as in the case of drops of syrup placed on the backs 

 of leaves and tentacles. Such movements may be 

 compared with the contortions which many vegetable 

 tissues undergo when subjected to exosmose. It is 

 therefore doubtful whether they throw any light on 

 the natural movements. 



If we admit that the outward passage of fluid is 

 the cause of the bending of the tentacles, we must 

 suppose that the cells, before the act of inflection, 

 are in a high state of tension, and that they are 

 elastic to an extraordinary degree ; for 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 Compositse, 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 



* ' Abhand. der Schles. Gesell. is given in the * Annals and Mag. 

 fiir vaterl. Cultur/ 18G1, Heft i. of Nat. Hist.' 3rd series, 18G"3, 

 An excellent abstract of this paper vol. xi. pp. 188-197. 



