38 RESEARCHES ON IRRITABILITY OF PLANTS 



shows in a striking manner how the speed first accelerates 

 and then slows down. 



The maximum movement is generally attained about 

 •5 second after the shock. The actual rate of the maxi- 

 mum responsive fall is here 40 mm. per second. The rate 

 of the responsive fall is modified by various conditions : — 



(i) The speed is greater under stronger stimulus. This 

 is well seen in fig. 12, where the lower one was taken under 

 stimulus intensity of i, and the upper one under stimulus 

 intensity of 4. The gentler slope of the lower curve, and 



Fig. 12. — Records giving apex- time in the response of 

 Mimosa. Lower curve is in response to stimulus i 

 and upper to stimulus 4 units. 



more abrupt rise of the upper, clearly show the greater speed 

 and vigour of the responsive movement under the stronger 

 stimulus. The curves show moreover that the amount 

 of this responsive movement is greater under stronger 

 stimulation. 



(2) In a fatigued condition the rate of the responsive 

 fall under constant stimulus is relatively slow. Thus 

 in a certain experiment, where the maximum rate of fall, 

 when fresh, was 30 mm. per second, the rate was slowed 

 down to 20 mm. per second in consequence of fatigue. 

 In another case the rate when fresh was 50 mm. per 



