556 PLANT RESPONSE 



These opposite effects at make and break, which I have 

 already demonstrated in the case of the pulvinar response 

 of vegetable tissue, will next be exhibited in a still more 

 striking manner in the case of growth-response. 



Anodic and kathodic effects on longitudinal growth. — 

 We thus pass from the question of the motile response of 

 pulvinated organs to the polar effects of currents on the rate 

 of growth. From a demonstration of the fundamental 

 action here, we shall be able to infer the curvature which 

 will be induced by the unilateral application of polar 

 currents in the growing organ. Experiments on growth, 

 especially when conducted by the Method of Balance, have 

 the unique advantage that the opposite responsive effects, of 

 expansion and contraction, are clearly distinguishable, and 

 not liable, under any circumstances, to be confused with the 

 natural process of recovery ; for, as I have explained 

 before, when a balanced horizontal record is taken of growth, 

 an expansion or acceleration of the rate of growth will give 

 rise to a deflection, represented, say, by an up curve. 

 Recovery to the normal condition will now be indicated by 

 a horizontal record. Contraction or retardation, similarly, 

 will be represented by a deflection of the record downwards. 

 Using this method, then, I have studied the effects of anode 

 and kathode on the growing regions of both root and shoot, 

 the second electrode being placed at a very great distance 

 from the first, so that its effect may be considered non- 

 existent. It may be said here that the results obtained 

 were the same for both root and shoot, and I shall now 

 describe the effects observed in the case of an experiment on 

 the root of Bindweed, using an E.M.F. of twenty volts. One 

 of the electrodes — a moist strip of cloth — is wrapped about the 

 growing region ; the second, as said before, being at a great 

 distance. The balanced horizontal record of growth is first 

 taken, and the growing region is made kathode. From the 

 down curve in the record (fig. 231), it will be seen that a 

 responsive retardation of growth is induced, which goes on 

 increasincf for a considerable time durinsf the maintenance 



