THE THEORIES OF PHOTOSYNTHESIS 1] 



111 a very carefully executed investigation, Miss Baker^^ has 

 studied quantitatively the effect of formaldehyde on plants. She 

 found that in the light formaldehyde is used for the synthesis of 

 food material; "the gain in dry weight produced was about half 

 the loss due to respiration, and an increase in the percentage of 

 formaldehyde in the air did not produce a corresponding increase 

 in dr}' weight after a certain concentration." The idea of Grafe 

 that chlorophyll acts as a protection against formaldehyde poison- 

 ing was shown to be incorrect, and that it is only in the light 

 that formaldehyde is not highly toxic. It was furthermore es- 

 tablished that the formaldehyde has no influence on the respira- 

 tion of the plant. 



From the experiments of Bokorny, Grafe, and Miss Baker, it 

 appears, therefore, that formaldehyde may function as a stage in 

 the process of photosynthesis, or otherwise serve the plant as 

 material from which food can be manufactured, but in order to 

 do this light energy is necessary. This would introduce an 

 entirely new phase in the theory of Baeyer. 



A modification of the Baeyer theory which combines therewith 

 some of the features of the old Liebig hypothesis has been ad- 

 vanced by Emil Baur.^'' He considers oxalic acid to be the first 

 reduction product of carbonic acid, the former substance is then 

 reduced to glycolic acid, which in turn on photolysis, yields 

 formaldehj^de. Baur arrived at this conclusion as the result of 

 his photochemical studies in which he found that the reduction 

 of carbonic acid to oxalic acid and then to formaldehyde, required 

 one-third the energy of the direct reduction of carbonic acid to 

 formaldehyde. 



It may be of interest now to note here briefly the results of 

 some of the experiments on various photochemical reactions bear- 

 ing on photosynthesis, carried out by the writer within the last 

 few years. Tucson has proved to be a most admirable place 



-* Baker, S. M., Quantitative Experiments on the Effects of Formaldehj'de on 

 Living Plants. Ann. of Bot. 27: 411-42, 1913. 



-' Baur, Emil, Ueber die Genesis der Kohlenhydrate. Naturwisseiischaften. 

 1:474-7, 1913. Zeitschr. physik. Chem. 63:683-710. 



