EXPERIMENTAL ARRANGEMENT 



315 



gravity, and there is thus no differential action as between 

 the two. But if the shoot be now rotated on itself, so that 

 one of these points is diametrically above and the other 

 below, a differential effect will be induced between the 

 upper and lower sides, the upper being the more excited. 

 In the following experiment I took a specimen of Eucharis 

 Lily, and fixed the entire plant horizontally (fig. 190). The 

 pivoted support allowed the responsive points A and B to 

 be at first lateral. 



' Owing to symmetry there w^as now no differential 

 action of gravity, nor any consequent electric variation 



Fig. 190. Experimental arrangement for subjecting the shoot to 

 geotropic stimulation, mechanical response being restrained. 



between the two. The specimen on its support was next 

 quickly rotated through 90°. An electric response was 

 perceived in about one minute, which went on augmenting 

 with time, the upper side being increasingly galvano- 

 metrically negative. By now rotating the specimen back 

 through 90°, the action of gravity is virtually removed. 

 The after-effect persists for two minutes, and after this the 

 response-curve show^s the usual recovery ' (fig. 191). 



Experiment 174. — I repeated the experiment by the 

 above method with Polianthes tuberosa, first by rotating 

 through 90° so that A was above. This gave the up-response 

 of galvanometric negativity of that side, which disappeared 

 on return to 0°. The rotation was next carried through 



