308 RESEARCHES ON IRRITABILITY OF PLANTS 



such as that of induction-shock. This can be seen in the 

 following record (fig. 151). The leaflet had been reduced by 



extreme sub-tonicity to a state 

 of standstill. A single electrical 

 stimulus of moderate intensity is 

 seen to give rise to a single re- 

 sponsive pulsation. Repetition of 

 the same stimulus gave rise once 

 more to a second response. 



In another instance, direct 

 tetanising electric shock of short 

 duration was applied to a leaflet in 

 a state of standstill. It is seen 

 (fig. 152) that this application of moderately strong stimulus 

 gave rise to renewed pulsation which persisted for a certain 

 length of time, even on the cessation of stimulus. 



Fig. 151. — Response of 

 Desmodium leaflet in 

 a state of standstill. 

 Single response to 

 single stimulus. 



The Latent Period 



Having thus found that a leaflet in a state of standstill 

 can be made to give response to instantaneous stimulation, 

 it is possible to determine the latent period. We have seen 

 that the latent period of the rhythmic cardiac tissue is, 



Fig. 152. — Multiple responses, under moderate tetanisation, 

 in leaflet originally at standstill. 



generally speaking, longer than that of the ordinary skeletal 

 tissue. In the plant, again, while the average value of the 

 latent period of ordinarily responding Mimosa is -i second 

 that of the multiple responding Biophytum is -4 second. 



