84 RESEARCHES ON IRRITABILITY OF PLANTS 



correspondingly larger and larger. This is clearly seen in 

 fig. 42, where the successive stimulations are applied at 

 intervals of seven minutes. 



Thus on subjecting a specimen in an optimum condition 

 to continuous stimulation, we should expect to find that 

 the extent of contraction due to tetanisation was but little 

 different from that due to a single stimulus. This is verified 

 by the following pair of records (fig. 43) showing the response 

 of a plant near optimum condition, under single stimulus 

 and under tetanisation. 



Summary 



The contractile response of the pulvinus of Mimosa 

 exhibits characteristics similar to those of the response of 

 muscle. 



Under normal conditions of the plant, and with suffi- 

 cient intervening periods of rest, the responses are found 

 to be uniform. 



The responses exhibit fatigue under conditions of incom- 

 plete recovery. 



The excitability of the plant in a sub-tonic condition is 

 enhanced by the action of the stimulus itself. Under such 

 conditions the responses exhibit a staircase increase. 



The anomalous erection, after a preliminary fall of the 

 leaf of Mimosa under continuous stimulation, is explic- 

 able on the common characteristics of response in plant 

 and animal tissues. In both, contraction is reversed to 

 relaxation under fatigue. 



