CHEMO-TROPISM AND GALVANO-TROPISM 553 



for it demonstrates that the fall of the leaf of Mimosa under 

 the action of a strong solution of salt was due, not to 

 plasmolytic, but to excitatory action. 



Polar effects of currents inducing growth-curvatures. — 



The galvano-tropic effects noticed by various observers in the 

 case of growing plant-organs have been contradictory, because 

 of the many complicating factors which might be expected to 

 arise, not only from the differences of anodic and kathodic 

 effects, but also from the varying points of application, and 

 intensity and duration of current. All the obscurities and 

 anomalies in connection with this subject will, however, be 

 found to disappear, when they are related to the funda- 

 mental polar effects, which have already been established as 

 applying to the excitation of plant-organs (Chapter XVI.). I 

 have shown that the kathode excites at make, and the anode at 

 break. I shall now be able to show further that the galvano- 

 tropic effects observed are all deducible from these. Inci- 

 dentally, too, owing to certain special advantages afforded 

 by growth-response, we shall be able to discover additional 

 effects which could not have been detected by the mechanical 

 response of the pulvinus alone. We have hitherto investi- 

 gated the polar effects of an electrical current acting on the 

 pulvinus as a whole ; but in order to bring these funda- 

 mental effects into the clearest prominence, and to establish 

 their universality, I shall now study (1) the reaction induced 

 in a limited area of the pulvinus ; (2) the variations of longi- 

 tudinal growth which result from the electrical actions of 

 anode and kathode ; and (3) the growth-curvature induced 

 by the unilateral action of anode or kathode on a growing 

 region. 



Localised polar effects on Pulvinus. — It is usually 

 believed that the responsive effect seen in a pulvinus is 

 entirely due to the excitability of the lower half of the organ. 

 I have already shown that it is really due to the differential 

 excitability of the upper and lower halves, and that the 

 upper half is also contractile under stimulus, though in a less 



