176 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. 160). 
E. Chlorophyll Content. 
So far we have dealt with environmental factors. It has been 
seen from Blackman’s analysis that the laws governing the intake 
of C0 2 in relation to these factors cannot yet be expressed in simple 
physical and chemical terms, but the experimental facts so far 
obtained can be conveniently expressed in terms of the action of 
limiting factors. 
Nor would it seem any more probable that an enquiry into the 
relation between an internal factor, e.g., chlorophyll, and the intake 
of carbon dioxide should yield results of any greater physico¬ 
chemical definiteness. In this section we shall deal in some detail 
with investigations made with a view of determining the relation 
between assimilation and chlorophyll content, and more particularly 
with the recent work of Willstatter and Stoll (1915). At present 
only preliminary accounts of the extensive work of these investigators 
are available ; consequently it is difficult to form a correct judgment 
of the value of the work and the validity of the arguments put 
forward in support of the hypotheses advanced. 
There is a strong contrast between Willstatter’s and Blackman s 
expression and generalisation of experimental results. While 
Blackman carefully avoids premature conclusions and tries to find 
non-committal expressions which will embody all his experimental 
results, Willstatter advances a simple definite hypothesis and 
attempts to obtain experimental data which will support his theory. 
In this section we shall only give Willstatter’s experimental 
data, in a later chapter we shall deal with the various theories of 
carbon assimilation which he has advanced. 
The main result of his work is a demonstration of the complexity 
of the processes of carbon assimilation ; an opinion which has often 
been expressed by earlier workers. For instance Pfeffer (1897) 
says that the chloroplasts “are only capable of assimilatory activity 
when all the component parts co-operate in an appropriate manner, 
and that the final result is produced not by a single reaction but by 
the agency of a complicated and self-regulatory mechanism.” 
Ewart (1896, 1897) and Pantanelli (1903) have published data 
which also tend to show that chlorophyll is not the only internal 
factor in the processes of carbon assimilation. 
