GEO-ELBCTRIC RESPONSE OF SHOOT 



449 



Stimulation : that (1) of Axial Rotation, and (2) of 

 Vertical Rotation. 



METHOD OF AXIAL ROTATION. 



In the method of Axial Rotation, the organ is held 

 with its long axis horizontal (Fig. 16(JH). We have seen 

 that the geotropic action increases with the angle which 

 the responding surface of the organ makes with the 



C Crpoi 



Fig. 166. — Diagrammatic representation of the Method of Axial Kotation H, and 

 of Vertical rotation V (see text). 



vertical lines of gravity. When the organ is held with 

 its length horizontal, the angle made by its two sides, A 

 and B, with the vertical is zero and there is thus no 

 geotropic effect. There is, moreover, no differential effect, 

 since the two sides are symmetrically placed as regards 

 the vertical lines of force. The plant is next rotated 

 round its long axis, the angle of rotation being indicated 

 in the circular scale. When the rotation is through +90 

 A is above and B below ; this induces a differential 

 geotropic effect, the upper side exhibiting excitatory electric 

 change of galvanometric negativity. 



