i88 RESEARCHES ON IRRITABILITY OF PLANTS 



variation, was alone induced '7 second after the application 

 of stimulus ; there was no indication whatsoever of the 

 later occurrence of the negative response. After the usual 

 interval of 20 minutes the next or middle record was taken 

 under the enhanced intensity of stimulus of 5 units. We 

 now observe the appearance of negative following the 

 positive. The positive took place '6 second and the negative 

 9'4 seconds after the application of stimulus. Finally, 

 when the stimulus-intensity was raised to 8 units, the 

 positive response took place at the same interval as 

 before, namely '6 second, but the negative or excitatory 

 response took place earlier than in the last case, that 

 is to say, after an interval of 4*6 seconds, instead of 

 9*4 seconds. 



In another experiment with a different specimen, the 

 positive response took place '5 second after the application 

 of stimulus of intensity 2 ; there was no negative response. 

 The point of application of stimulus was kept always 



Table IV. — Effect of Intensity of Stimulus on the Positive and 

 Negative Responses in Mimosa 



the same — namely, 10 mm. When the intensity of stimulus 

 was increased to 4, the negative response was found to 

 occur after the positive. The former took place '5 second. 



