r 5 ° Ingvar Jorgensen and Walter Stiles. 
I 
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). 
Fig. 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 10°C is 2-1. By 
