RESPONSE OF LEAVES 



227 



that the excitatory current always flows from the more to the 

 less excited portions of the tissue. 



Another effect observed by Burdon Sanderson was, that 

 on cutting the petiole across, the existing normal leaf-current 

 was increased, the amount of this increase being determined 

 by the length of the petiole cut off, in such a way that the 

 shorter the petiole left, the stronger the leaf-current became. 

 In Nature (vol. x. p. 128), he suggested an explanation of this 

 phenomenon. In the leaf of Dioncea^ as already said, there 

 is a resting-current in the stalk, opposed in direction to that 

 in the leaf. Thus * the electrical conditions on opposite sides 

 of the joint between stalk and leaf are antagonistic to each 

 other; consequently, so long as the leaf and stalk are united 

 each prevents or diminishes the manifestation of electro- 

 motive force by the other.' He thus inferred that the pro- 

 gressive removal of the antagonistic element, by section of the 

 stalk, would serve to enhance the intensity of the leaf-current. 



Taking the ordinary leaf of Ficus religiosa> I have myself 

 been able to obtain results precisely similar to those described 

 in Dioncea, by making successive sections of the petiole, at 

 shorter and shorter distances from the point of junction. 

 The leaf-current at each section underwent an increment. 

 The parallelism of the two sets of effects will be seen from 

 the following table. 



Ficus LEAF. DION/EA LEAF (BURDON SANDERSON). 



Length of stalk Galvanometric deflection 





Burdon Sanderson's suggested explanation that the suc- 

 cessive augmentations of the leaf-current were due to suc- 

 cessive removals of the antagonistic element, by section, is 



Q2 



