EEECTRIG RESPONSE IN PLANTS 2a 
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 
