304 



PLANT RESPONSE 



leaflets, at first quiescent, break into a sustained series of 

 uninterrupted pulsatory movements, which they kept up 

 throughout the maintenance of the condition of high tempera- 

 ture. It was interesting also to observe the quickening of 

 vibration by absorption of energy. The pulses were at first 

 slow, each having a period of four minutes, but they became 

 steadily more rapid, till they had reached a frequency of two 

 vibrations in a minute. A continuous record of these periods 

 was made during one hour, and the following tabular state- 

 ment exhibits the results : 



Table showing Periods of Successive Pulsations in Biophytum 

 when Temperature is Raised to 37 C. 



Having thus found that a high temperature was favour- 

 able to the initiation of automatic movements in Biophytum, 

 I was next desirous of determining the minimum temperature 

 at which such responses could be induced. For this purpose 

 I took a fresh specimen of Biophytum, and cautiously raised 

 the temperature of the chamber from 23 C. upwards. When 

 29 C. had been reached, I obtained the first pulse of auto- 

 nomous response, the period being rather slow — that is to say, 

 8*5 minutes — and by the time the temperature had gone up to 

 35 C. this period had become shortened to two minutes. We 

 find here a phenomenon identical with that of Desmodium, 

 where the frequency of vibration is found to be increased with 

 rising temperature. 



