PLANT RESPONSE 49 
(fig. 27) under strong stimulation. I was able in some 
cases to trace this process of gradual reversal, by 
continuously increasing the intensity of stimulus. It 
was then found that as the stimulus was increased, the 
positive at a certain point underwent a reversal into 
the normal negative response (fig. 28). 
The plant thus gives a reversed response under 
abnormal conditions of staleness. 1 have sometimes 

Fic. 28.—Apnnormat PosiTIvE PAssinc IntTO Normal NEGATIVE IN A STALE 
SPECIMEN OF LEAF-STALK OF CAULIFLOWER 
Stimulus was gradually increased from 1 to 10, by means of spring-tapper. When 
the stimulus intensity was 10, the response became reversed into normal 
negative. (Parts of 8 and 9 are out of the plate.) 
found similar reversal of response when the plant is 
subjected to the abnormal conditions of excessively 
high or low temperature. 
Radial E.M. variation. We have seen that a current 
of response flows in the plant from the relatively more 
to the relatively less excited. A theoretically important 
experiment is the following: A thick stem of plant 
stalk was taken and a hole bored so as to make one 
contact with the interior of the tissue, the other being 
B 
