SENSITIVENESS AND IRRITABILITY OF PLANT ORGANS. 153 



of an incTuctional 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 drawn 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 lumj^s. 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. 



