36 chap. iv. variation of temperature 



Method of Discontinuous Observation 



Determination of cardinal points of temperature. — The 

 cardinal points are not the same for different plants ; even 

 in the same species they are modified by the climate to 

 which the plants have been habituated. The results 

 obtained in the tropics must necessarily be different from 

 those in colder climates. The following experiments were 



Fig. 15. Records of growth, on stationary plate, 

 at different temperatures. 



carried out in Calcutta in the spring season, when the 

 average temperature is about 30° C. 



Experiment 10. The optimum temperature. — High mag- 

 nification records of the growth of Kysoor were taken on a 

 stationary plate for selected temperatures of 30°, 35°, 40°, 

 and 45° C, each of these being kept constant during the 

 period of observation. The records (fig. 15) show that the 

 rate of growth increases with the rise of temperature to an 

 optimum, above which the rate undergoes depression. In 

 the different records given in the figure, the time-interval 



