34 PLANT RESPONSE 



for the electrical experiment a plant in which the state of 

 excitation is independently manifested by mechanical response. 

 If now these electrical and mechanical responses be indeed 

 only two different expressions of the same thing — that is 

 to say, of a molecular disturbance and recovery which is 

 concomitant to excitation and recovery from excitation — 

 then we should expect that, on taking a simultaneous record, 

 the two responses would be shown to be initiated at the same 

 moment, and to bear some general resemblance to each other. 

 In the following record it will be seen that this is found to be 

 the case (fig. 26). 



To recapitulate : let us take the concrete example of the 

 Mimosa leaf. When the pulvinus is excited, owing to the 



FlG. 26. Simultaneous Mechanical (m) and Electrical (e) Responses in Biophytum 

 These responses are seen to take place at the same moment. 



molecular change induced by stimulus, there is an expul- 

 sion of water, or negative turgidity-variation, and in the 

 absence of restraint this is attended by the normal negative 

 mechanical response, or fall of the leaf. If, now, electrical 

 connections have been made, one with the pulvinus, and the 

 other with a distant point on the stem, it will be found that 

 the excitatory change is attended by a strictly concomitant 

 electrical change, the current of response flowing away from 

 the excited point, which in other words becomes galvano- 

 metrically negative. 



All these events will perhaps be more easily realised if 

 we remember that excitation, in the typical case of Mimosa 



