SENSITIVENESS AND IRRITABILITY OF PLANT ORGANS. 153 



of an inductional apparatus always produce more or less deeply 

 extending changes in the form of the plasm, which resumes 

 its normal character if the power exerted be not too strong. 

 The protoplasm immediately forms itself under the induc- 

 tional shocks into lumps or balls ; and, moreover, often sends 

 club-shaped extensions with great suddenness and energy 

 into the cell lumen, and immediately brings the circulation to 

 a standstill. The rotation returns, however, after a period of 

 rest, the extensions are draw^n in, and the former net-shaped 

 distribution of the protoplasm is restored, even when the 

 whole mass of the plasm has been changed into a number of 

 colourless balls and lumps. If the current is allowed to go 

 only through a limited portion of the cell, then the streaming 

 stops also in this tract only, and that, too, amid the formation 

 of the lumps and balls. 



" A sudden increase and decrease of temperature acts in 

 the same way ; there ensues a formation of drops, a cessation 

 of the current, etc. Yet even here a return to the normal 

 constitution takes place if no real coagulation of the proto- 

 plasm has occurred. On the contrary, the current often ensues, 

 after its recommencement, with a greatly heightened speed, 

 and even boisterously. The grains, etc., found in the cell-sap 

 outside the protoplasm are, however violently the current 

 may flow, in no way influenced by it, but remain at rest." 



M. E. Heckel has described * the effect of a mechanical 

 irritation on the protoplasm of the cells of the filaments of 

 Berheris. He says that the cells of the irritable part are 

 arranged in a parallel manner, being longer than broad. 

 Their contents are of a yellow colour, and disseminated 

 throughout the whole cavity, but especially applied upon 

 the walls. After receiving the excitation, the same cells, 

 the surface of which is striated transversely, are massed 

 * Bull, de la Soc. Bot. de Fr., torn, xxi., 1874, p. 208. 



