PLANT RESPONSE 



their parallels in the plant ; not merely in the sensitive 

 Mimosa, but even in the undemonstrative radish. 



The discussion of the various theories of response must 

 be left to the professed physiologist : it is sufficient here to 

 emphasise the more general conception underlying the whole 

 work and increasingly verified as it proceeds. Not simply 

 is the mechanical response to stimulus expressed in obvious 



FIG. 8. The ' staircase ' enhancement of response in plant. 



movements like the fall of the Mimosa leaf, but by mechanical 

 response of organs of ordinary plants when their record is 

 magnified, as by the optical lever. Such excitatory reaction 

 caused by external stimulus expresses itself not only in 

 mechanical movements, but also by generation of electric 

 current, and by change of electric conductivity; and 

 doubtless also in other ways, both physical and chemical. 

 Just as the passage of one and the same electric current may 

 be manifested not only by the swing of the galvanometer 

 needle, but also in chemical change or in terms of light 

 and heat, or by sound, as from an electric bell, according 



