Dioncea Musctftula, Ellis. 31 



be taken account of, Sachs concluded 1 " that the condition 

 of turgescence of the cells depends upon the protoplasmic 

 utricle opposing the expulsion of the endosmotically absorbed 

 water, even under high pressure," and he follows Sanderson 

 in expressing the opinion that "the extensibility of the 

 cellulose walls plays an important part" in effecting con- 

 traction after the permeable protoplasmic utricle has per- 

 mitted an escape of liquid. Gardiner's experiments further 

 prove that plasmolysis is the important factor, and the follow- 

 ing statement of his sums up the position: "From certain 

 observations on Dioncea and Mimosa the author is led to 

 believe that there also movement is made possible by t he- 

 establishment of sudden and different conditions of turgid ity 

 of different cells, such differences being occasioned by the 

 induced porosity of the protoplasm of certain of these cells. 

 These phenomena occur perhaps in all cases of movement." 



But the water that escapes after stimulation from the cells 

 on or near the upper leaf surface must be transferred to some 

 other region, and the amount necessary to be transferred need 

 not be great. The presence, in large leaves especially, of 

 loose intercellular passages between every pair of bundles 

 suggests that liquid may escape into these. But we would 

 suggest for further consideration the possibility that the pores 

 on the surface of the irritable joint cells are open, and that 

 through these the protoplasm can rapidly eject, or allow the 

 passage of, minute quantities of liquid sufficient to disturb 

 seriously the equilibrium ; since we have indicated that the 

 protoplasmic masses of the joint cells are connected by inter- 

 cellular threads with those of the base, as are the latter again 

 with the epidermal and gland cells. It might be imagined 

 that minute drops escaping could readily be seen, but sev- 

 eral difficulties stand in the way. In attempting to bring 

 the objective of the microscope into focus on the joint cells 

 the leaf as a rule closes ; failing this the shining cell sur- 

 faces reflect light so much that excreted liquid would read- 

 ily be overlooked. The experiments performed by Darwin 



1 Physiology of Plants, Eng. ed., 1887, p. 653. 



- Roy. Instit. Lectures, " Nature." Vol. XXVI. p. 356 ct seq. 



