ABSORPTION OF CARBON 29 



preceded by another process going on directly in the light-absorb- 

 ing molecule of the chlorophyll. The products of this process 

 serve then for the reduction of carbon dioxide. 



We are very little acquainted with the internal chemistry of 

 the reactions taking place in photosynthesis. Until recently the 

 most commonly accepted idea was the formaldehyde theory 

 advanced by Baeyer in the 'seventies of the last century. Accord- 

 ing to this theory, the first product of the assimilation of carbon 

 dioxide and water is formaldehyde, the formation of which is rep- 

 resented by the equation: 



C0 2 + H 2 -> HCHO + 2 . 



The formaldehyde obtained is polymerized under the influence 

 of alkalies into a hexose, which was first observed by Butlerow: 



6H-CHO-*C 6 Hi 2 06. 



Various arguments have been advanced against Baeyer's 

 theory. The most serious of them is that formaldehyde is utilized 

 with great difficulty by the plant for the synthesis of carbohydrates 

 and therefore can hardly be considered as an intermediate product 

 of assimilation. Considerations of this kind, as well as modern 

 chemical data, have caused Willstatter to alter considerably the 

 Baeyer's scheme. It is now supposed that the primary reaction 

 is the union of carbon dioxide with the chlorophyll nucleus. This 

 union of chlorophyll with carbon dioxide, absorbing directly the 

 radiant energy, passes over into a peroxide form in the following 

 way: . 



RMg + HO— C— OH -> RHMg— 0— C— OH 



I I 



-*RHMg— 0— CH< I 



X) 



->RMg + H-CH0 + 2 



where RMg, the molecule of chlorophyll, is finally restored to its 

 original state. The formaldehyde thus originated is no longer 

 retained by the chlorophyll molecule, but is condensed into 

 glucose according to the above illustration. 



Willstatter' s theory explains clearly the catalytic action of 

 chlorophyll, which up to this time remained somewhat mysteri- 



