Theories of Willstdtier. 163 



N MgX 



/^ \ 

 HC CH 



II II -> 



HC CH 



The pyrrole magnesium derivatives have thus — analogous with 

 sodiumacetic ester — behaved like any Grignard body with binding 

 of the metal to carbon. 



Chlorophyll can be regarded as of the same class of organo- 

 magnesium compounds, and it seems unjustified to draw a sharp 

 line between magnesium phenyl iodide, pyrrole magnesium iodide 

 and chlorophyll, only chlorophyll is characterised by a greater 

 stability of magnesium towards water than the ordinary organo- 

 magnesium compounds on account of the complex binding of the 

 metal. 



This comparison does not require that the pigment in the 

 process of assimilation should take the carbon dioxide into its 

 molecule. This can be prevented by substitution in the magnesium- 

 carrying pyrrole nuclei. Rather the function of chlorophyll may be 

 imagined thus : that the carbon dioxide is attracted by the affinity 

 of the magnesium compounds, and that its reduction is effected jsy 

 the chlorophyll component a in the process which uses the absorbed 

 light energy. Chlorophyll a is hereby oxidised to chlorophyll b, and 

 this is again transformed to the first component with evolution of 

 oxygen. Between the two components an equilibrium condition is 

 obtained. 



It is possible that this evolution of oxygen either takes place 

 direct or that the yellow pigments, carotin and xanthopbyil take 

 part in the re-formation of chlorophyll a. As the yellow pigments 

 constantly accompany the green pigments in the chloroplasts, it is 

 probable that they have a function. Perhaps this is to regulate the 

 ratio of the chlorophyll components, perhaps by the withdrawal of 

 oxygen from chlorophyll b by carotin, this oxygen being then evolved 

 from xanthophyll by means of the action of an enzyme." 



It will be seen that Willstatter here first defends his conception 

 of chlorophyll as a Grignard body. In spite of his elaboration of 

 this conception, it appears to us that his arguments amount to this : 

 In the Grignard syntheses a good many curious things may happen. 

 Carbon assimilation is a curious process which involves the complex 

 organic magnesium compound chlorophyll. Why should not 

 carbon assimilation be a Grignard synthesis 



