^^6 PLANT RESPONSE 



In the next experiment cooling was produced more 

 suddenly, by application of cold water at about 4° C. to 

 the pulvinus. We observe in this case how the quick 

 reduction to the thermo-tonic minimum reduced the ampli- 

 tude till the pulsation had come to a stop. I then allowed 

 the leaf to return gradually to the temperature of the room, 

 and it is very interesting to note the effect of increasing 



Fig. 141. Efl'ect of Rapid Cooling by Ice-cold Water 



Normal pulsations recorded to the left. Effect or application of ice-cold 

 water is seen in the production of diminished amplitude and abolition 

 of pulsation. Gradual return to the temperature of the room revives 

 the pulsation in a staircase manner, the period remaining approximately 

 constant. Note that cooling, in this and previous figure, displaced the 

 pulsation in a downward or contracted direction. Gradual warming, 

 conversely, is seen in this figure to produce the opposite displacement 

 towards relaxation. 



absorption of thermal energy from its surroundings. The 

 increased energy thus absorbed is seen to give rise to 

 increased amplitude of oscillation, in a staircase manner, 

 which gradually approaches the original pulsation (fig. 141). 

 In both these figures it will be noticed that cooling dis- 

 places the pulsation in a downward or contracted direction. 

 And in the last series of fig. 141 we see that the raising of the 



