328 RESEARCHES ON IRRITABILITY OF PLANTS 



the record in each case being continued for a period of 

 20 minutes. At a low temperature the pulsation is apt to be 

 somewhat irregular, hence the unequal amplitude in the 

 successive pulsations at 19 C. 



It is apparent that while at 19 C. there were 3! pulsa- 

 tions, at 23* 5 C. the number had been increased to 4 J, 

 and at 28*5° C. to 6 pulsations. 



Fig. 171. — Effect of rise of tem- 

 perature on the pulsation of Des- 

 modium gyrans. Time-marks 

 below indicate intervals of 1 

 minute. 



Fig. 172. — Effect of rise of 

 temperature on a different 

 leaflet. 



Taking a more vigorous specimen, I obtained records 

 for 12 minutes each at temperatures of 28 , 5° C, 31*5° C, and 

 34-5° C. It will be seen that while at 28-5° there were only 

 4 pulsations, these had become increased to 6| pulsations at 

 3i"5° and to 10 pulsations at 34*5° C. The other noticeable 

 feature is the marked diminution of amplitude with the 

 rise of temperature (fig. 172). 



Instead of taking isolated records at different tempera- 

 tures, I next raised the temperature of the plant-chamber 

 very gradually, by careful manipulation of the heating 

 current, and obtained a record with a different specimen. 

 In this way the temperature was raised continuously from 



