ELECTRIC RESPONSE IN PLANTS 33 



vibration as the stimulus, obtained strong responses at 

 both ends A and B. I then immersed the same stalk for 

 a short time in hot water at about 65 C., and again 

 stimulated it as before. But at neither A nor B could 

 any response now be evoked. As all the external con- 

 ditions were the same in the first and second parts of 

 this experiment, the only difference being that in one 

 the stalk was alive and in the other killed, we have 

 here further and conclusive proof of the physiological 

 character of electric response in plants. 



The same facts may be demonstrated in a still more 

 striking manner by first obtaining two similar but 

 opposite responses in a fresh stalk, at A and B, and then 

 killing one half, say B, by immersing only that half of 

 the stalk in hot water. The stalk is replaced in the 

 apparatus, and it is now found that whereas the A half 

 gives strong response, the end B gives none. 



In the experiments on negative variation, it was 

 tacitly assumed that the variation is due to a differential 

 action, stimulus producing a greater excitation at the 

 uninjured than at the injured end. The block method 

 enables us to test the correctness of this assumption. 

 The B end of the stalk is injured or killed by a few drops 

 of strong potash, the other end being uninjured. There 

 is a clamp between A and B. The end A is stimulated 

 and a strong response is obtained. The end B is now 

 stimulated, and there is little or no response. The 

 block is now removed and the plant stimulated through- 

 out its length. Though the stimulus now acts on both 

 ends, yet, owing to the irresponsive condition of B, there 

 is a resultant response, which from its direction is found 



D 



