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 3I 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 i 

 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, 3i'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 J pulsations at 

 31*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 



