4:6S LIFE MOVEMENTS IN PLANTS 



electric contacts were made at two points diametrically 

 opposite to each other. Displacement of the shoot from 

 vertical to horizontal position induced excitatory change 

 of galvanometric negativity at the upper side of the organ, 

 demonstrating the effect of direct stimulation of that side ; 

 this excitatory reaction of the upper side finds independent 

 mechanical expression in the induced contraction and 

 concavity of that side of the organ. 



I employ a similar electric method for detection of 

 geotropic excitation of the root, responses to geo tropic 

 stimulus being taken at the root-tip and also at the zone 

 of growth in which geotropic curvature is effected. I 

 shall now proceed to give a detailed description of the 

 characteristic .electric responses of the tip and of the growing 

 region. 



The two diametrically opposite contacts at the tip 

 will l)e distinguished as a and i, the corresponding points 

 higher up in the growing region being A and B. When the 

 root is vertical the electric conditions of the two diame- 

 trically opposite points are practically the same. But 

 when the root is rotated in a vertical plane through -f 90° 

 a geo-electric response will be found to take place ; the 

 direction of the responsive current disappears when the 

 root is brought l)ack to the vertical. Rotation through 

 -90° gives rise again to a responsive current, but its 

 direction is found reversed. 



GEO-ELECTRIC RESPONSE OF THE ROOT-TIP. 



Experitnetit 182. — I took the root of the bean plant and 

 made two electric contacts with the diametrically opposite 

 points, a and b, of the root-tip at a distance of about I'D 

 mm. from the extreme end. Owing to the very small 



