PLANTS UNDER MECHANICAL STIMULUS. 287 
at 60°C. After this treatment the responses are completely 
abolished. As all the external conditions were the same in the 
first and second parts of the 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 that half 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. 
Responses to Single Stimuli. 
In animal tissues three types of responses are observed :— 
(1) Uniform responses, where succeeding stimuli of equal 
intensity give rise to equal responses. 
(2) Staircase effect, where stimuli of equal intensity give 
rise to succeeding increased responses. 
(3) Responses exhibiting fatigue, where equal stimuli give 
rise to diminishing responses. 
Uniform responses.—Unitorm responses may be obtained with 
some plants when in good condition. For studying the effect of 
various agencies in modifying response, it is essential to find 
specimens where the responses are regular. I have often met 
with such uniform responses from selected specimens of carrot 
and radish. The record given below shows how absolutely 
regular are such responses (fig. 8). 
Fig. 8. 
Uniform responses (Radish). 
“ Staircase” effect.—The following record (fig. 9) shows how 
i . ; ained though the 
In some cases increasing responses are obtained thoug 
