PLANT RESPONSE 



69 



eould be introduced. I had chosen a specimen which 

 gave regular response. On the introduction of steam, 

 with the consequent sudden increase of temperature, 

 there was a transitory augmentation of excitability. 

 But this quickly disappeared, and in five minutes the 

 plant was effectively killed, as will be seen graphically 

 illustrated in the record (fig. 42). 



Before f After 



FIG. 42. EFFECT OF STEAM IN KILLING RESPONSE 



The two records to the left exhibit normal response at 17" C. Sudden warming 

 by steam produced at first an increase of response, but five minutes' expo- 

 sure to steam killed the plant (carrot) and abolished the response. 



Vibrational stimulus of 30 applied at intervals of one minute; vertical 

 line = 'l volt. 



It will thus be seen that those modifications of vital 

 activity which are produced in plants by temperature 

 variation can be very accurately gauged by electric 

 response. Indeed it may be said that there is no other 

 method by which the moment of cessation of vitality 

 can be so satisfactorily distinguished. Ordinarily, we 



