REVIEW OF RESPONSE, SIMPLE AND MULTIPLE 719 



the animal and vegetable may be seen, lies in the respective 

 effects induced at anode and kathode ; for example, em- 

 ploying the leaflets of Biophytum 'as experimental specimens, 

 and using a moderate E.M.F., we find that the excitatory 

 depression of the leaflets takes place at the kathode at make, 

 and at the anode at break. The antagonistic effects of 

 anode and kathode are further seen in the fact that while the 

 kathode-make excites, the anode-make depresses. It is 

 owing to this latter fact that an excitatory wave is blocked 

 during transit at an anodic area (p. 233). 



Another very interesting difference between anode and 

 kathode, both at make and break, is seen in the fact that 

 at make, while an induced contraction takes place at the 

 kathode, an induced expansion occurs at the anode ; at break 

 both these effects are reversed, there being now an expan- 

 sion at the kathode, and contraction at the anode. Expansion 

 at make, moreover, attains its maximum in a short time, 

 while the kathodic contraction is relatively strong and per- 

 sistent. These fundamental effects find appropriate expression 

 in the response of growth. Thus, the unilateral application 

 of the anode induces expansion, acceleration of growth, and 

 resultant convexity, w r hile the effect of the kathode is to 

 induce contraction, retardation of growth, and resultant con- 

 cavity (p. 558). 



Owing to the fact that kathodic action is stronger than 

 anodic, a feeble or moderate current flowing through the 

 soil exerts a predominant excitatory action on the roots, by 

 which the suctional activity of the plant is increased. The 

 result is an increased rate of growth of the plant, which is 

 independent of the direction of the current through the soil 

 (p. 560). 



The normal polar effects which have been described take 

 place under the action of a moderate electromotive force. 

 When this is excessively high, however, the normal effects 

 are, or tend to be, reversed. In this reversal there appear to 

 be two stages — the A stage and the B stage. In the A stage 

 both anode and kathode excite at make ; but in the B stage, 



