PHOTOSYNTHETIC COEFFICIENT FOR TEMPERATURE 141 



I have previously referred to the remarkable similarity 

 of the modifications of photosynthetic activity to those of 

 other activities of the plant under external variations. In 

 regard to the effect of temperature, the irritability of 

 Mimosa is at its maximum at 34 C, which is therefore the 

 optimum. In fig. 38 (p. 139) are given records of responses of 

 Mimosa under a definite testing stimulus, during a complete 

 cycle of temperature variation from 23 to 37 C. and back 

 once more to 23 C. The maximum response is seen to take 

 place at 34 C. 



I have also determined * the optimum temperature for 

 growth in the tropical plant Scirpus Kysoor. The curve of 

 growth of this plant is reproduced side by side with the 

 photosynthetic curve (compare figs. 39, 40). The similarity 

 between the two curves is very striking. 



Determination of the Photosynthetic Coefficient 



for Temperature 



The rise of photosynthetic activity in the middle range 

 of variation of temperature is practically uniform, and the 

 coefficient may be found in two ways : first, from measure- 

 ments from the physiological zero — discussed in a sub- 

 sequent chapter— and, second, by dividing the increase of 

 activity by the increase of temperature. 



A T — A/ 

 K = — V • • • ( J ) 



T — t K ' 



where A T is the activity in c.mm. per hour for the higher 

 temperature T, and A^ is the activity for the lower tempera- 

 ture t 



Examples : 

 Specimen II. 



Activity at temperature 21 -3 C. . . 191*13 



28°-3C. . . 337 -46 



-rr 337'46 — IQI-I3 



K = » 2 r? = 20 -9 



28-3 - 21-3 



1 Plant Response (1906) ; Life Movements of Plants (1917). 



