558 



PLANT RESPONSE 



The generalised law of polar excitation in plants is as 

 follows : The kathode induces contraction at make, and expansion 

 at break. The anode induces expansion at make, and contraction 

 at break. 



Galvano-tropic response. — From the demonstration just 

 made of the fundamental polar effects on growth, we can 

 easily infer the responsive curvature that would be induced 

 in a growing organ by the unilateral action of anode or 

 kathode. I shall, however, show that the effects directly 

 observed are in strict conformity with these deductions. For 

 these experiments I took the long scape 

 of Crinum Lily, and on its growing 

 region I applied one electrode, the other 

 being connected with a distant point 

 On now making one side of the growing 

 region anode, there was induced on that 

 side a sudden and short-lived responsive 

 expansion and convexity, seen in the 

 up curve (fig. 232). At break, the 

 opposite effect occurred, consisting 

 partly of contraction and partly of 

 natural recovery. The current was 

 now reversed, and the effect of the 

 unilateral kathode-make was the induc- 

 tion of a very active and relatively long- 

 continued contraction and concavity, to 

 be seen from the down curve. The 

 kathode-break next gave rise to the 

 opposite effect, which was made up 

 partly of expansion, and partly of natural recovery. Thus 

 in these galvano-tropic effects of currents on growing organs, 

 we find what is simply a special case of the fundamental 

 polar effects of currents on growth in general. 



The indirect effect of polar excitation. — For the pur- 

 pose of clearly demonstrating the fundamental action of 

 currents, I have taken in the first place the simplest cases of 

 the direct action of anode and kathode on the growing 



Fig. 232. Responsive 

 Curvature in Scape of 

 Crinum Lily by Uni- 

 lateral Application of 

 Anode and Kathode 



aw = expansion at anode- 

 make ; Ad m contrac- 

 tion at anode-break ; 

 Km = contraction at 

 kathode-make, and 

 Kb = ' expansion at 

 kathode-break. 



