154 Carbon Assimilation. 



biological text-books. Here again we agree with Spoehr who 

 expresses as his opinion, " In recent years this hypothesis has 

 largely directed the course of the investigations in this subject, 

 and it seems to the writer, to the detriment of critical and inde- 

 pendent thinking on the broader aspects thereof." 



B. Hypothesis of Baeyer. 



We shall in what follows only deal with Baeyer and his 

 followers as briefly as possible, as those interested in this branch 

 of this subject will have no difficulty in finding ample references to 

 the literature in text-books and journals. 



Before Baeyer's time the chemists, for instance, Liebig (1843b), 

 Kolbe and Schmidt (1861), and Berthelot (1864), appear to have 

 been of the opinion that in the process of assimilation organic acids 

 were produced from which carbohydrates were subsequently 

 formed. In the course of a paper, entitled " Ueber die Wasserent- 

 ziehung und ihrer Bedeutung fiir das Pfianzenleben und die 

 Gahrung," Baeyer threw out a suggestion as to the formation of 

 formaldehyde as an intermediate product of assimilation, a hypothesis 

 which was really based on Butlerow's observation (1861) that 

 trioxymethylene (a condensation product of formaldehyde) on 

 heating in alkaline medium yields a syrupy product with some of the 

 properties of sugars. 



We give below Baeyer's suggestion in a translation of his own 

 words. 



" The general assumption in regard to the formation in the 

 plant of sugars and related bodies, is that in the green parts carbon 

 dioxide under the action of light is reduced and by subsequent 

 synthesis transformed to sugar. Intermediate steps have been 

 sought in organic acids : formic acid, oxalic acid, tartaric acid, 

 which can be regarded as reduction products of carbon dioxide. 

 According to this opinion, at those times when the green parts of 

 the plant are most strongly subjected to the action of the sun's rays, 

 a strong accumulation of acids should take place, and these should 

 then gradually give place to sugar. As far as I know this has 

 never been observed, and when it is remembered that in the plant 

 sugars and their anhydrides are formed under all circumstances, 

 whereas the presence of acids varies according to the kind of plant, 

 the particular part of it and its age, then the opinion already often 

 put forward, that the sugar is formed directly from the carbon 

 dioxide, increases in probability. 



