356 Temperature and Carbon- Dioxide Assimilation. [July 29, 



respiratory allowance could then be arrived at by determining the 

 CCVproduction of a number of similar leaves in the dark. 



At moderately high temperatures the respiration of the actual 

 single leaf employed was determined, where possible, both before the 

 assimilation experiment and after, when the CCVproduction is always 

 much increased. 



At the highest temperatures rapid decline of vitality made this 

 procedure impossible, and only an approximate value could be 

 arrived at. 



5. Taking all these factors into consideration, a satisfactory series of 

 assimilation maxima for the whole range of temperature was finally 

 obtained. 



The amount is just determinable at 6 C., and then rises rapidly 

 with higher temperatures, giving a curve which is convex to the 

 temperature abscissa. The curve is similar to the accepted curves for 

 the effect of temperature on respiration, and it rises more and more 

 steeply at higher temperatures certainly up to 38 C. 



At temperatures about this point the leaf is not capable of main- 

 taining its initial high rate of assimilation for any long time, so that 

 the values obtained for successive hourly estimations with the same 

 leaf form a rapidly declining series. The higher the temperature the 

 shorter the duration of the period of maximal assimilation, and it 

 becomes experimentally impossible with hourly estimations to obtain 

 the maximal value at temperatures close to the fatal temperature of 

 45 C. The final numbers actually obtained, which can be only sub- 

 maximal, show a conventional "optimum" at a temperature about 

 38 C., with a subsequent very rapid decline. 



