88 Ingvar Jorgensen and Walter Stiles. 
The second part of his theoretical consideration is more 
interesting, as for the first time we have a suggestion which 
involves the presence of two different chlorophylls. Although this 
fact was brought out by the work of Stokes, all subsequent theorists 
avoided the difficulty by neglecting it. As Willstatter insists that 
the absolute value of the green pigments and the ratio between 
them remains constant, 1 there must be a mechanism which keeps 
the system in equilibrium. The main agency in this, Willstatter 
suggests, is the yellow pigments assisted by suitable enzymes. 
Willstatter’s conception of the chlorophyll apparatus as 
constituting a system in dynamic equilibrium is of course very 
interesting. However, as long as our knowledge of photochemical 
reactions and enzyme reactions in the chloroplasts is as imperfect 
as it is at present, this theory of Willstatter’s cannot be accepted 
as more than a suggestion. 
Finally we shall consider the theories expounded by 
Willstatter in his latest publications (1915, b-d). One of the 
suggestions put forward in these papers we have already mentioned 
(Chapter IV, Section E), namely, the reasonable suggestion that 
carbon assimilation consists of a photochemical process and an 
enzymatic process. This conclusion was derived from plant 
physiological experiments with leaves in various conditions. 
Further work with isolated chlorophyll was performed in 
support of his elaboration of the theory, but it is not clear whether 
this most recent theory replaces the earlier one we have already 
dealt with, or whether it is intended to supplement it. At least 
no mention is any longer made of chlorophyll as a Grignard 
synthesizing agent, nor is any account taken of the two chlorophylls, 
nor of the yellow pigments. Willstatter considers now that a dis¬ 
sociable compound of chlorophyll and carbon dioxide is formed, but as 
it is formed in the dark he assumes that the function of light is simply 
to produce an isomer of higher energy content. This assumption 
carries in its train a number of equally wild speculations which the 
reader will find in the translation we give below of the summary of 
the theory. 
“ As it is seen from the above, the entrance of carbon dioxide 
into the chloroplast takes place by means of an absorbing substance. 
The apparatus acts as a carbon dioxide accumulator, as it brings 
1 See Chapter II, Section F. Further figures in support of this statement 
are given by Willstatter and Stoll (1915 b, p. 336) for strongly assimilating 
leaves under artificial conditions, 
