440 COMPARATIVE ELECTRO-PHYSIOLOGY 



be galvanometrically positive in relation to the lower, the 

 direction of the current in the horizontal shoot being from 

 below to above. And finally, in the third stage, we have the 

 geotropic stimulation effectively overpowering and reversing 

 this downward movement. And since it is the upper side 

 that is now geotropically excited to an effective extent, we 

 find that that side becomes galvanometrically negative. 

 Thus, the electrical indication, like the mechanical, gives 

 in this ultimate stage the characteristic response of the 



FIG. 269. Photographic Record of Geo-electric Response in the Scape 

 of Uriclis Lily laid horizontally 



In the first phase of response, the current is from the upper surface To the 

 lower, the upper being galvanometrically positive. After fifty minutes, 

 A the excitatory geotropic effect reverses the current, which is now 

 ascending, of from below to above, the excited upper-surface being 

 galvanometrically .. negative. (Compare corresponding mechanical 

 record, fig. 268.) 



plant-tissue to gravitational stimulus. The excitatory 

 effect is now exhibited mechanically by the contraction 

 and concavity, and electrically by the galvanometric 

 negativity of the upper side of the horizontally laid shoot 

 (fig. 269). These similarities between the mechanical and 

 electrical records will be seen on comparing this figure with 

 fig. 268. We have thus seen that, owing to secondary 

 mechanical disturbances, the proper exhibition of the true 

 geotropic response is delayed. And from this it is difficult 

 to say how quickly the geotropic response follows the dis- 



