32 



PLANT RESPONSE 



course, in the opposite direction, that is from B to A.' The 

 excited point A is thus electro-positive, but in physiological 

 text-books it has been ambiguously termed negative. In 

 order therefore to keep touch with the older terminology and 

 yet avoid the implied error, I shall refer to the excited point 

 as ^ galvanometrically negative.' 



If the B end of the specimen be now excited, the direction 

 of the responsive current will be reversed. With greater 

 intensity of stimulus the electrical response will be found 

 The record of such responses is 

 obtained on a revolving drum. 



correspondingly increased 



{a) (/') 



by following the deflection of 

 a spot of light reflected from 

 the galvanometer mirror in a 

 manner precisely similar to 

 that employed with the Optic 

 Lever (fig. 24). 



Method of transmitted 

 stimulation.— In the simple 



23. Electrical Response in Plant case just described, the tissue 



was stimulated directly and 

 locally at the end A, say by 



Current of response %vlicn 



A is stimulated -> 

 Current of response ivhen 



B is stimulated <- 



Fig. 



by Method of Block 



[a) The plant is clamped at c, between 

 A and B. 



{h) Responses obtained by alternately torsional vibration. There is, 

 stnnulating the two ends, btnviula- ' 



tion of A produces upward response, howevcr, another method of 



and that of B downward. transmitted stimulation, by 



which a stimulus, — say by application of cut, or hot wire, 

 or electrical shock, — is given at a point X some distance 

 away, say to the right. The excitation now travels with a 

 velocity characteristic of the specimen, and when it reaches 

 the proximal electrode produces galvanometric negativity 

 of that point. The interval of time which elapses between 

 the application of stimulus and response will therefore depend 

 on the velocity of transmission and the distance of the point 



' The failure to understand this point cleivrly has been the source of many 

 grave errors in some physiological text books. From the fact that the current in 

 the external circuit is seen to flow in the direction of A, it has been erroneously 

 supposed that that point is negative, or zinc-like. See Bose, Response in the 

 Living and Non- Living. 



