24 COMPARATIVE ELECTRO-PHYSIOLOGY 



we take a petiole or stem, and making suitable electrical 

 connections (fig. 15), apply stimulus, say by contact of hot 

 wire at the point marked x . After a short interval, necessary 

 for the excitation to traverse the intervening distance, an 

 electrical response is obtained, of galvanometric negativity. 

 It is thus seen that the electrical response of ' ordinary ' is of 

 the same sign as that of ' sensitive ' plants, and that in both, 

 again, it is like that of animal tissues. 



I shall next proceed to demonstrate a very important 

 proposition : namely, that all effective forms of stimulation 

 induce an identical excitatory response of galvanometric 

 negativity. Any sudden change of environmental conditions 

 may constitute an efficient stimulus. Such are : sudden rise 



FIG. 15. Method of Transmitted Stimulation 



Stimulus applied to the right at x . Excitation reaches right contact first, 

 causing galvanometric negativity of the 



of temperature ; any variation of pressure, whether of tension 

 or compression ; mechanical blows or torsional vibration ; any 

 prick or cut ; the application of a chemical agent, such as 

 acid ; the application of light ; the incidence or variation of 

 electrical currents ; and, lastly, the action of gravity. The 

 stimulatory action of all these agents has already been 

 demonstrated in my work on ' Plant Response,' ] the excita- 

 tion induced being there shown to find expression in 

 appropriate mechanical movements. In the present volume 

 I shall deal more particularly with the electrical reactions 

 which they induce. The effects of the stimulating action of 



1 Bose, Plant Response as a Means of Physiological Investigation, 1906. 



