i62 RESEARCHES ON IRRITABILITY OF PLANTS 



point of application of stimulus or the motile sensibility of 

 the responding pulvinus. For this reason cold is applied 

 locally on the petiole, half-way between the point of appli- 

 cation of stimulus of induction-shock and the pulvinus. 

 The experimental plant was highly sensitive on account 

 of the favourable summer season. An intensity of stimulus 

 of '5 unit applied at a distance of 30 mm. from the pulvinus 

 was found to be effectively transmitted. The intensity of 

 stimulus actually employed was 2 units, which was maximal. 

 A strip of cloth 10 mm. in breadth was wrapped round the 



Fig. 90. — EfEect of cold in inducing retardation and arrest of transmission : 

 (i) Normal record ; (2) Retardation due to slight cooling ; (3) Arrest 



^ , of conduction brought about by intense cold ; {4) Record of direct 

 stimulation. 



petiole midway between the point of stimulation and the 

 pulvinus. This was for the purpose of local application 

 of cold by means of cooled water or by means of small 

 fragments of ice. 



Successive records were then taken at intervals of 

 20 minutes, which is more than sufficient for complete 

 recovery from previous stimulation. Record i in fig. 90 

 gives the time-interval between the application of 

 stimulus and response under normal conditions. There are 

 20 '5 seconds spaces, each space representing -i second. The 

 latent period is -15 second. The true time of transmission 

 is thus 1-9 second for 30 mm. ; the transmission time 



