EFFECT OF VARIATION OF TEMPERATURE 53 



the response attains a certain maximum value (fig. 10 

 (a)). After recovery the plant is subjected to an increased 



Fig. 10. Maximum Response of Mimosa under Increasing 

 Intensity of Electric Stimulus 



intensity of stimulus, and a second maximum (b) is obtained, 

 larger than (a). A still higher intensity of stimulus 

 gives rise to a third maximum (c), greater than either (a) 

 or (6). 



Effect of Variation of Temperature 



Up to a certain optimum, rise of temperature 

 causes a general enhancement of physiological activity, as 

 exhibited in different modes of response. It gives rise to 

 an erectile movement of the leaf of Mimosa, to an in- 

 creased rate of the ascent of sap, to quicker frequency of 

 pulsation of the leaflet of Desmodium gyrans, and to an 

 enhancement of the rate of growth. In all these modes 

 of response a decline occurs at a temperature above the 

 optimum. 



There is also a definite minimum temperature for arrest 



