THE THEORIES OF PHOTOSYNTHESIS 5 



Berthelot,^ in 1864, suggested the dissociation of carbon di- 

 oxide into carbon monoxide and oxygen, 2 C02^2CO+02, and 

 a subsequent reduction of the CO, as the first step in photosyn- 

 thesis. By means of the silent electric discharge Loeb'" actually 

 broke up CO2 in this way, and has formulated an elaborate hy- 

 pothesis of the photosynthetic process based on his experiments. 

 Briefly, his results that are of interest here can be described as 

 follows : 



1. 2C02-^2CO+02. 2. CO+HsO-^HCOOH. 



3. CO+HsO^COa+Ha. 4. Hs+CO^HCOH. 



Thus, by using something to take up the oxygen (as e.g., chloro- 

 phyll solutions), Loeb obtained formaldehyde and formic acid, 

 with ease and in quantity, from carbon dioxide and water by the 

 use of the silent electric discharge. Of special interest is the faci 

 that Loeb also noticed the formation of glycolyaldehyde from 

 2H2 +2CO->CH20HCHO. The further synthesis of the hexoses 

 from glycolyaldehyde is a relatively simple matter. The basic 

 principle in this scheme is the breaking down of CO2 into CO 

 and O2, and the subsequent reduction of the CO. While from a 

 chemical view point these observations are of great interest, the 

 plant physiologist very naturally finds great difficulty in the ap- 

 plication of these findings to the living plant as he knows it. 

 The electrical conditions both in the plant and in the atmosphere 

 surrounding it, have not been found to be of such a nature as to 

 have their homologue in the currents used by Loeb. As yet we 

 have no reliable data of a photoelectric effect which might trans- 

 form the light energy into electrical energy in a manner that would 

 bring about the above mentioned results. There is no evidence 

 that in the photosynthetic process any wave lengths are utilized 

 that lie outside of the visible portion of the spectrum, such as 

 might be associated with the silent electric discharge, and to 

 which Loeb ascribes the reducing action in his experiments. 

 Furthermore, it is not without its importance that while Loeb 



' Berthelot, M., Lecons sur les methodes g^n^ral de synthese. Paris, 1864. 

 '"Loeb, W., Zur Kentnis der Assimilation der Kohlensaure. Zeitschr. f. 

 Elektrochem. 11:745 52, 1905; 12:282-312, 1906. 



