Carbon Assimilation 
155 
coefficient increases with decreasing temperature. This may he due 
to some other factor coming into play and it is a general phenomenon 
in life processes (cf. e.g., Krogh’s temperature-metaholism curve in 
Fig. 7). Again in the case of many chemical reactions the temper¬ 
ature coefficient gradually decreases with rise of temperature, and 
this may perhaps be the case in carbon assimilation. In any case 
Blackman was more justified in assuming as an approximate 
temperature-coefficient at temperatures above 25 n C the value 
obtained from 5°C to 25°C than the value between —6°C and 5°C. 
It must be kept in mind that the theoretical curve of initial assimi¬ 
lation maxima is necessarily an approximation. 
Temperature. 
Fig. 12. Curves showing the relation between temperature and rate of 
enzyme action. (After Duclaux). 
Kanitz further criticises the method of obtaining the initial 
assimilation values obtained by carrying back the time-assimilation 
curves to zero time. He asserts that the numbers so obtained give 
the amount of assimilation which actually takes place during the 
first hour of the experiment, whereas the number actually required 
is the assimilation which would take place in an hour if the initial 
rate of assimilation remained constant throughout that hour. This 
criticism also is due to imperfect consideration of Blackman’s 
curves. The first measurements of assimilation were made by Miss 
Matthaei from 1£ hours to 2£ hours after the experiment was 
started. The number so obtained can be taken as approximately 
representing the rate of assimilation 2 hours after the commencement 
