SUMMARY 143 



The thermometric minima for various activities of 

 tropical plants are more or less definite. In the photo- 

 synthesis of Hydrilla the critical point for arrest varies in 

 different specimens from 9°«5 to n° C. 



The average optimum temperature for photosynthesis 

 in Hydrilla, under moderate intensity of light of about 

 1200 lux, is 30 C. But under increased intensity of sunlight 

 the optimum point is raised to 33 C. This is of the same 

 order as the optimum point, 34 C, for maximum response 

 in Mimosa. The optimum point for growth of tropical 

 plants is also about 33 C. 



The temperature coefficient obtained by the differential 

 method is : 



A T -A; 



K 



T -t 



The value of the coefficient is found to be about 20 -4. 



A rise of temperature of 7 C. is found to double the 

 photosynthetic activity of Hydrilla. For a rise of io° C. 

 the increase is 2 -2 times. 



The activity at a higher temperature may be found from 

 the following formula : 



At = A; + K (t - 1) 



