164 Carbon Assimilation. 



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,' 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. 



WiUstatter'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 WiUstatter'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 



' 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. 



