8o Carbon Assimilation. 



coefficient increases with decreasing temperature. This may be due 

 to some other factor coming into play and it is a general phenomenon 

 in life processes (cf. e.g., Krogh's temperature-metabolism curve in 

 Pig. 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''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. 



TeMP1-1!ATU«E. 



Fig. 12. Curves showing the relation between temperature and rate of 

 enzyme action. (After Duclau.x). 



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 If 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 



