Temperature. 



75 



These two tables show very clearly the different relation 

 between assimilation and time at temperatures below and above 

 25"C. Whereas the assimilation proceeds at a constant rate at 

 8-8°C as long as the experiment is continued, at 37'5°C there is a 

 rapid falling off in the rate of assimilation throughout the experiment. 

 A time factor comes into play. The facts observed in Miss Matthaei's 

 experiments indicate the three following laws in regard to the time 

 factor (Blackman, 1905). 



E 



.20 



(>0 



SO 



30 

 10 



-lo'c 



10" 



Tehperatuhe. 



20" c 



Fio. 9. Curve illustrating the effect of temperature on assimilation of 

 Cherry Laurel under the influence of light of different intensities. 1, unit 

 intensity of light ; 2, twofold intensity ; 4, fourfold Intensity. (After Matthaei). 



1. At high temperatures the initial rate of assimilation 

 cannot be maintained, but falls off regularly. 



2. The higher the temperature the more rapid is the falling 

 off. 



3. The falling off at any given temperature is fastest at first 

 and subsequently becomes less rapid. 



It thus becomes impossible to measure the highest possible 

 assimilation at any temperature, but Blackman estimates this initial 

 value of the assimilation by two methods. Firstly, below 25°C no 

 time factor is involved and the assimilation numbers obtained 

 therefore give a correct value of the initial values of the assimilation, 

 The curve obtained from these numbers is a van't Hoff curve in 

 which the temperature coefficient for a rise of lO'C is 2'1. By 



