Hypothesis of Baeyer. 1 5 7 



seems certain that various monosaccharides can be produced from 

 formaldehyde under certain conditions. But these conditions, 

 generally high temperature and alkaline medium, are not the 

 same as those existing in the plant, so that it is impossible to 

 argue from these experiments " in vitro " as to the possible con- 

 densation of formaldehyde to sugar in the leaf. Nor do we knovf 

 of any photochemical or enzymatic reactions which could bring 

 about this change. 



3. It has been urged that carbon assimilation should proceed 

 in absence of carbon dioxide if an intermediate product were 

 given as nutrient. Thus Loew (1889) and BoUorny (1888-191 1) insist 

 that Spirogyra in absence of carbon dioxide, but in presence of 

 the sodium bisulphite compound with formaldehyde can form 

 starch, while Grafe (1909, 1911) and Miss Baker (1913) 

 have urged that plants can so utilise gaseous formaldehyde itself 

 if this is present in the air in a concentration sufficiently low to 

 prevent toxic effects. This only takes place in the light ; in the 

 dark formaldehyde is toxic. Spoehr established that formaldehyde 

 vapour mixed with air is quickly oxidised to formic acid in sun- 

 light, so that Grafe's and Miss Baker's experiments could only be 

 used in favour of a formic acid theory of assimilation. 



Moreover, the utilisation of a substance by the leaf is no proof 

 that that substance is an intermediate pi-oduct in carbon assimila- 

 tion, as we know of several substances which can be utilised by 

 the plant, such as glycerine and sugars not normally found in the 

 leaf, but which nevertheless are not generally supposed to be 

 intermediate products. 



Again it has not been found possible to utilise carbon-mono- 

 oxide in assimilation, as has been shown for example by de Saussure 

 (1804), Boussingault (1868) and Krash^ninnikoff (1909). 



Thus it is seen, as Spoehr expresses it, that Baeyer's hypothesis, 

 " though alluring on account of its simplicity, is by no means as well 

 established as many writers on the subject would have us believe.'' 

 Indeed it seems to us that the words of Sachs written 35 years 

 ago (1882, 1887) are as applicable now as on the day when 

 they were written; "whether it is right to claim, with Beitlelot 

 and Kekuld, formic acid or some other member of the formyl group 

 as the first product of assimilation, on account of its simple con- 

 stitution, I hold as at least very questionable; and it has hitherto 

 been proved by nothing." 



