THE THEORIES OF PHOTOSYNTHESIS 15 



potassium carbonate formed sugar in the dark as well as in the 

 sunlight. It seems quite doubtful, therefore, that the condensa- 

 tion of formaldehyde to sugar can take place in the plant in the 

 sense of the Butlerow reaction. 



In the foregoing experiments it was noticed that the main re- 

 action was the formation of formic acid from the formaldehyde. 

 Even in neutral solution the formaldehyde was very readily 

 oxidized in the sunlight. 



It was furthermore established that formaldehyde vapor mixed 

 with air is quickly oxidized to formic acid in the sunlight. In 

 view of this fact the experiments of Grafe and of Miss Baker take 

 on a very different aspect. The question immediately arises, 

 were the plants in these experiments appropriating any formal- 

 dehyde at all, or was it the formic acid (formed by oxidization 

 of formaldehyde in the sunlight) that served as a source of car- 

 bon; and is the phenomenon of the reduction of the toxicity of 

 formaldehj'de by light to be explained by the fact that this 

 substance is converted into formic acid in the light? 



I have studied the action of gaseous formic acid on green 

 plants in the light, and have found that although this acid is 

 quite toxic to the roots, the chlorophyllous portions develop 

 normally in an atmosphere of formic acid, show an appreciable 

 gain in drj^ weight, and also form starch. 



In conclusion, some of the failings of the formaldehyde hypoth- 

 esis, both from a chemical and physiological aspect have been 

 pointed out, and an effort has been made to show that this hypoth- 

 esis, though alluring on account of its simplicity, is by no means 

 as well established as many writers on the subject would have us 

 believe. This criticism has as its object not the overthrowing of 

 ideas that have proved to be fruitful, but rather the urging of 

 experimentation and observation, unfettered by hypotheses, on a 

 subject that requires for its investigation the masterly application 

 of many branches of science and the frank cooperation of the 

 most skilled workers in these various fields. 



It has been shown that carbon dioxide and water are easily 

 reduced to formic acid by means of light, that from this latter 



