GEO-ELECTRIC RESPONSE 



441 



placement of the hypothetical statolithic particles. I have 

 been able to overcome this difficulty, which at first appears 

 very great, in the following way. It has been shown that 

 the state of excitation, even when all mechanical expression 

 of it is restrained, may be detected by galvanometric nega- 

 tivity. Those secondary effects, due to mechanical dis- 

 turbance, which mask for a time the excitatory effect of 

 gravitational stimulus, may thus be eliminated completely by 

 restraining all movement of the shoot. The problem thus 

 resolves itself into the fixing of an experimental shoot, say 

 the peduncle of Uriclis lily in such a way that mechanical 



FIG. 270. Experimental Arrangement for Subjecting Organ to Geotropic 

 Stimulus, Mechanical Response being Restrained 



response is completely restrained. The next point is to 

 subject the specimen, at a given moment, to the stimulus of 

 gravity, and record the consequent electric response. 



I shall now describe the experimental method by which 

 these conditions were successfully met. It is clear that when 

 any two points are acted on symmetrically by the force of 

 gravity, there is no resultant geotropic action. This is the 

 case in regard to two diametrically opposite points, A and B, 

 situated laterally on an erect shoot. When the shoot is laid 

 horizontally, two lateral points are again acted on sym- 

 metrically by the force of gravity, and there is thus no differ- 

 ential action as between the two. But if the shoot be now 

 rotated on itself, so that one of these points is diametrically 



