THE VIEWS OF WILLSTATTER AND STOLL 45 



this kind of evidence is of direct value then the weight of evi- 

 dence is on the side of formic acid. 



The Production of Sugar from Formaldehyde. The evi- 

 dence for the condensation of formaldehyde to hexose sugars 

 in the laboratory under the influence of various catalysts is 

 convincing : but valuable though such evidence be, especially 

 in providing points d'appui, it does not follow that such a 

 sequence obtains in the plant. The formaldehyde hypothesis 

 requires a hexose as the initial sugar : the general opinion 

 of those who have concerned themselves with the final products 

 of carbon assimilation is that sucrose, not a hexose, is the 

 first recognizable sugar. 



For these reasons, Baeyer's hypothesis, a theory which has 

 lived for fifty years, cannot be considered to be substantiated. 



Willstatter and Stoll's views regarding the mechanism of 

 carbon assimilation may now be summarized. 



They agree with Baeyer that formaldehyde is the inter- 

 mediate link between the carbon dioxide supplied to the plant 

 and the carbohydrate synthesized with the help of chlorophyll. 

 It has already been pointed out that their chief argument in 

 support of this view is based upon the constant value, I, 

 obtained for the so-called assimilatory ratio; this ratio is 

 obtained by dividing the volume of carbon dioxide supplied to 

 the plant by the volume of oxygen evolved ; according to 

 theory, the complete reduction of carbon dioxide, i.e. the 

 removal of both oxygen atoms, might proceed through succes- 

 sive stages of oxalic, formic and glycollic acids down to the 

 formaldehyde stage, but in that case the assimilatory ratio 

 would be respectively 4, 2, or 1-33 for each of the acids men- 

 tioned, whereas formaldehyde alone requires the value I which 

 is the figure actually obtained in a number of experiments 

 under most varied conditions. This argument is not based 

 upon the actual experimental demonstration of formaldehyde 

 isolated from assimilating leaves, and, with regard to this 

 particular question, these authors have revised many of the 

 statements made by previous workers. It will be remembered 

 that repeated attempts have been made to demonstrate the 

 formation of formaldehyde by the action of chlorophyll upon 

 carbon dioxide outside the plant. The earlier work of Usher 

 and Priestley, demonstrating the formation of this substance in 



