240 COMPARATIVE ELECTRO-PHYSIOLOGY 



lamina, were both alike shown to be the result of the alge- 

 braical summation of a definite excitatory current with the 

 two opposite-directioned resting-currents. The positive 

 variation of the leaf-current, again, on section of the petiole, 

 has been traced to the same cause, namely the stimulatory 

 action of mechanical section, giving rise to an excitatory 

 current which was summated with the existing leaf-current. 

 Finally the positive response of the concave surface ot 

 Dioncea has been shown to arise, not from any specific 

 difference between plant and animal response, but from the 

 fact that in this particular case it was the indirect hydro- 

 positive effect of stimulus that was transmitted, inducing an 

 action opposite to that of true excitation. 



