CHAPTER VIII 



THEORIES OF ASSIMILATION 



Photochemical Character of Assimilation 



The observations mentioned in the last chapter fully confirm 

 a fact that has long been known, namely, that assimilation 

 through chlorophyll has the character of a photochemical 

 reaction. It cannot be accompUshed without light and nothing 

 can take the place of light. 



Between the molecules of water and of carbon dioxide, 

 and the products of combination elaborated in the green 

 parts of plants, intermediate compounds, which have not 

 yet been identified with certainty, are formed. 



Obviously chlorophyll also has a chemical role, but the 

 hypotheses that we shall consider are not fully proved and 

 photosynthesis, in spite of the numerous studies that have 

 been made of it, remains a still mysterious natural 

 phenomenon. 



The overall reaction can be written as follows: 



H20+C02+light=CH20+02 



The compound CHgO is formaldehyde or formol. 



Klein and Werner (1926) claim to have demonstrated, 

 although the fact is still in dispute, the presence of formol in 

 leaves which assimilate normally. Generally, the two sides 

 of this chemical equation are multiplied by 6 ; the compound 

 (CH20)6 is a sugar — glucose — or one of its isomers. 



But as we do not know whether the immediate product 

 of photosynthesis is this sugar or another polymer molecule, 

 we shall keep to the simplest formula indicated, at the same 

 time stressing that it does not necessarily imply the formation 

 of formol, but perhaps only of a polymer combination of 

 formol, or of a molecule of similar composition. 



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