72 RESEARCHES ON IRRITABILITY OF PLANTS 



slows down, and the leaf becomes for a time stationary at 

 the apex. These varying rates of fall are seen in the 

 growing and then in the diminishing intervals between the 

 dots. 



Fatigue 



If instead of giving the full period of rest necessary 

 for complete protoplasmic recovery, the period of rest be 



Fig. 33. — Uniform responses of Mimosa ; stimuli applied at 

 intervals of 15 minutes. 



shortened, we obtain a diminution in the height of response 

 indicative of fatigue. This is well seen in fig. 34. The first 

 three uniform responses here — taken, as it is unnecessary 

 to repeat, under uniform stimulation — were recorded at 

 intervals of 15 minutes each. The intervals between succes- 

 sive stimulations were now shortened to 10 minutes, which 

 at once results in a fatigue-diminution of the height of 

 responses. The second three responses appear crowded 

 together, owing to the shortening of the time allowed for 

 record. The time of recovery, after the third of these 

 responses, was again restored to its first value of 15 minutes, 

 and we see at once the reversion of the response to its 

 original height. A similar exhibition of fatigue is also seen 



