GEO-ELECTRIC RESPONSE OF SHOOT 



447 



The direct method of contact described above is 

 extremely convenieni in practice ; the resistance of contact 

 is considerably reduced, and there is no possibility of its 

 variation during the necessary process of rotation of the 

 plant for subjecting it to geotropic action. 



GEO-ELECTRIC RESPONSE OF THE UPPER AND LOWER 

 SIDES OF THE ORGAN. 



We have next to discover the electric change induced 

 by geotropic stimulus on the upper and lower sides of 

 the organ. For this purpose it is necessary to find a 

 neutral point which is not affected by the inclination of 

 the organ from vertical to horizontal position. For the 

 present experiment, I employed the flower of the water 

 lily Nymphcea, the peduncle of which is sensitive to geo- 

 tropic action. One electrical contact is made with a 



Fig. 165. — Diagrammatic representation of geo-electric response. The middle 

 figure represents vertical position. In figure to the right rotation through +90^ 

 has placed A above with induced electric change of galavauometric negativity of 

 A. In the figure to the left, rotation is through -90^ A being below: the electric 

 response is by induced galvanometric poaitivity of A. For simplification of 

 diagram, vertical position of sepal is not always shown in the figure. 



sepal, which is always kept vertical ; the other electric 

 contact is made at the point A, on one side of the 

 flower stalk (Fig. 165). On making connections with a 

 sensitive galvanometer a very feeble current was found, 

 which was due to slight physiological difference between 



