156 Carbon Assimilation. 



incomplete, it is impossible to draw conclusions from experiments 

 in which the conditions are clearly so different. 



The experiments in relation to Baeyer's hypothesis fall into 

 three groups : — 



1. Experiments on the formation of formaldehyde in (a) 

 systems containing carbon-dioxide and water, (6) systems con- 

 taining carbon-dioxide, water and chlorophyll, (c) leaves. 



2. Experiments on the formation of sugars from form- 

 aldehyde. 



3. Feeding experiments with formaldehyde. 



1. (a) The production of formaldehyde from carbon dioxide and 

 water in the absence of chlorophyll certainly seems possible under 

 certain conditions. For instance, Fenton (1907) and D. Berthelot 

 and Gaudechon (1910) have each succeeded in reducing carbon- 

 dioxide to formaldehyde under appropriate conditions, but there is 

 no evidence that these conditions are in the least comparable to those 

 in the plant. References to further work in this connection will 

 be found in the paper by Spoehr already cited, in which this side of 

 the question is critically dealt with. 



(&) Experiments dealing with the photochemical production 

 of formaldehyde from systems containing carbon dioxide, water 

 and chlorophyll have all been made with crude chlorophyll, and in 

 most cases oxygen has not been removed from the system. In 

 order to repeat these experiments critically we ourselves extracted 

 some pure chlorophyll (a + b). The results obtained in the experi- 

 ments made with this pure chlorophyll are recorded in a paper by 

 Jorgensen and Kidd (1916). It was found that the production of 

 formaldehyde was always due to the oxidation of chlorophyll. In 

 systems containing only carbon dioxide, water and chlorophyll no 

 formaldehyde is produced. 



(c) Pollacci (1899—1907), Grafe (1906), Kimpflin (1907) and 

 R, J. H. Gibson (1908) contend that formaldehyde can be identified 

 in leaves after illumination, while Curtius and Pranzen (1912) 

 contend that other aldehydes are produced, e.g., a yS hexylene 

 aldehyde, but in view of the critical experiments of Pincke (1913) 

 and Spoehr (1913) it is clear that under various conditions a large 

 number of substances in the plant will produce aldehydes. 

 Thus experiments of this type do not give support to the formal- 

 dehyde hypothesis. 



2. In view of the experiments of Butlerow (1861), Fischer 

 (1888, 1889) and Loew (1889), and above all Nef (1910, 1913) it 



