270 PHOTOSYNTHESIS 



This criticism would apply to the theoretical speculations of Stoklasa 

 and Zdobnicky -^ in their first schematic representation of the photosyn- 

 thetic reactions. In a second publication (to be discussed later) hydrogen 

 is not included in their equations. What becomes of the hydrogen, sup- 

 posedly formed from glucose when the plant is in the dark or formed in 

 chlorophyll- free cells is another question of much importance. Certainly 

 it is not liberated as such in any quantity and one is obliged to assume that 

 under these conditions it combines with oxygen to form water, and that 

 in the light and in the presence of chlorophyll the active hydrogen, instead 

 of combining with oxygen, reacts with carbon monoxide to form formal- 

 dehyde. 



In the original theory of Baeyer the role of hydrogen was the reduc- 

 tion of carbon monoxide to formaldehyde ; the carbon dioxide is split into 

 carbon monoxide and oxygen by the action of light. Thus half of the 

 oxygen which is emitted in the photosynthetic process is already accounted 

 for, the question being how the other atom of oxygen is set free. There 

 can be little doubt that this comes from water either directly or indirectly. 

 That the carbonic acid is reduced directly by "active" hydrogen, as is 

 assumed by PoUacci has little support. On the other hand, Zenghelis '^~ 

 has reported that when hydrogen is passed through filter paper (extrac- 

 tion thimbles) in water saturated with carbon dioxide, formaldehyde is 

 produced. The assumption is that on passing through the fine pores of 

 the filter paper or within the pores, the hydrogen is split into atomic 

 hydrogen which reduces the carlDonic acid. Besides formaldehyde, Zeng- 

 helis reports also having obtained sugar in this manner; the amount of 

 the latter is greater when the action takes place in light. The author may 

 be permitted to state that he has repeated the experiments of Zenghelis but 

 obtained only negative results. 



While there are, no doubt, these difficulties in the mechanism of the 

 photosynthesis reaction as originally stated in the Baeyer theory, the 

 assumption of formaldehyde as an intermediate step has appeared very 

 plausible and gained many adherents resulting in various modifications 

 of the original mechanism. Thus, Nef -^ on the basis of his theory of 

 methylene dissociation assumes a splitting of carbonic acid into carbon 

 monoxide and hydrogen peroxide. 



OC(OH)2 ?± OC< + H2O2 -> OCHo -f O2 



This implies a reduction of the carbon monoxide by the hydrogen peroxide. 

 The formation of the latter substance in the photosynthetic reaction has 

 also been assumed by Erlenmeyer and has been used by Usher and Priest- 

 ley ^® in their schematic representation of the process as follows : 



=° Stoklasa and Zdobnicky, Biochem. Zeit., 30, 448 (1911). 

 "Zenghelis, Covipt. rend., 170, 883 (1920) ; 171, 167 (1920). 

 ^ Nef, ^wn. C/i<?m., 357, 253 (1907). . ^. . 



"^ Usher and Priestley, Proc. Row Soc. 77 B, 369 (1905). Phipson, Chcm. News, 

 50, 2>7, 288 (1884). 



