*44 
Ingvar Jorgensen and Walter Stiles. 
CARBON ASSIMILATION. 
A Review of Recent Work on the Pigments of the 
Green Leaf and the Processes connected with them. 
By Ingvar Jorgensen and Walter Stiles. 
(>Continued from p. 135). 
B. Temperature. 
From the researches of van’t Hoff it is well known that the 
relation between temperature and the reaction velocity of a good 
many chemical reactions can be expressed in a simple way, revealing 
the fact that in many cases the reaction rate at moderate temper¬ 
atures is increased 2 or 3 times for a rise of 10°C. On the other 
hand, animal physiologists have shown that although a smooth 
temperature-metaholism curve can be constructed which gives the 
relation between temperature and respiration, yet this curve does 
not obey the van’t Hoff rule. Similar curves have been obtained 
for plant respiration by Kuijper (1910) and for one aspect of plant 
growth (Leitch, 1916). Such a curve is shown in Fig. 7 and its 
relation to true van’t Hoff curves with different coefficients (Q 10 ) 
exhibited. Some consider such a curve as made up of portions of 
several van’t Hoff curves having different constants (Putter, 1914). 
Krogh (1916) points out that it is not very probable from a priori 
considerations that the van’t Hoff rule should be followed, as we 
have to do, not with a simple chemical reaction, but with a complex 
series of reactions possibly taking place in a heterogeneous system. 
And even if the difference between the heterogeneous system and 
a system is solution could be neglected, yet the shape of the 
curve would still be affected if a limiting factor were operative. 
Thus oxygen pressure in the tissues might be a limiting factor. 
Owing to Blackman’s recognition throughout his work of the 
effect of limiting factors, our knowledge of the relation between 
temperature and carbon assimilation is much clearer. It is recognised 
by Blackman that in investigating the influence of temperature on 
carbon assimilation, no other factor must be limiting the rate of the 
process, as in such a case, the amount of the carbon assimilation is 
simply dependent upon the value of the limiting factor and is not 
related to the temperature. 
The influence of temperature on carbon assimilation is described 
in two papers, one by Miss Matthaei (1904) and a second by 
Blackman and Matthaei (1905). In these papers will be found a 
