CHEMO-TROPISM AND GALVANO-TROPISM 559 



responding region itself ; but when similar applications are 

 made, at a point distant from the responding region, we can 

 foresee the fact that variations of these effects will occur. 

 Thus the kathode-make, whose direct action induces contrac- 

 tion and concavity, will now, acting from a distance, bring 

 about, by means of expelled water, the indirect effect of 

 expansion and convexity. This can be demonstrated by 

 selecting a growing and undetached petal of CJiampaca, in 

 which the growing region is diffuse. The lower half of this 

 petal is held in a clamp, the free upper half being attached 

 to the Optic Lever for observation of its responsive movement. 

 If now we make one side of the clamped half kathode (the 

 other electrode being connected with the rest of the plant at 

 a distance), then, at make of kathode, the indirect effect of 

 stimulation, reaching the same side of the free end of the 

 petal, gives rise to expansion and convexity — that is to say, 

 the opposite effect to that which would have occurred had 

 that region been directly subjected to kathodic action. The 

 effect of the kathode on a distant growing organ is thus an 

 acceleration of growth. 



The effect on growth of ' electrification ' of soil. — 

 Empiric attempts have been made to discover whether the 

 maintenance of an electrical current through the soil might 

 or might not be made to have the effect of accelerating the 

 growth of plants. This problem can only be satisfactorily 

 solved, however, from accurate knowledge of the direct and 

 indirect effects on growth of currents under the given condi- 

 tions. Since growth is determined by the direction of current, 

 it is not clear that currents flowing through the soil from right 

 to left, or left to right, could give rise to a single effect. 

 Looking, again, at the root, on which the current acts, we can 

 see that one side will be anode and the other side kathode, 

 and as the actions of these are known to be antagonistic, it is 

 at first sight difficult to see how there can be any resultant 

 excitatory effect at all. 



We are, however, enabled to obtain a clear understanding 

 of the subject by an attentive comparison of the responsive 



