292 PHOTOSYNTHESIS 



stances to which he ascribed the formula CH3 . CHOH . CO . CH3 and 

 CH3 . CHOH . CHO. Rouge ^^ has also endeavored to find support for 

 the glycollic aldehyde theory. He also failed to find the slightest trace 

 of formaldehyde, but by means of p-nitrophenylhydrazine obtained very 

 small amounts of the p-nitrophenylhydrazone of glycollic aldehyde from 

 different species of leaves. However, too much value cannot be placed 

 upon any of this evidence as supporting the theory of glycollic aldehyde 

 as an intermediate product in photosynthesis. In mixtures, color reactions 

 are often deceiving and a few hundredths of a gram of a hydrazone also 

 do not offer very conclusive evidence. 



Glyoxylic acid, COOH . CH : O, has also been suggested as an inter- 

 mediate product. Its presence in plants has been reported by several. '^^ 

 Whether this compound is actually associated with photosynthesis has, 

 however, not been established. The same applies to the presence of 

 glycollic acid which has been found in a wide variety of plants, both in 

 the leaves and fruits." 



The presence of formic acid in leaves has also not been definitely 

 established and there exist many contradictory reports. A question of 

 importance in this regard is whether in those cases in wliich formic 

 acid has been found, it was originally in the leaves or was formed from 

 other substances through the process of distillation. In the older litera- 

 ture '^^ there occur frequent references to the presence of formic acid, 

 but its occurrence has since been questioned, especially in leaves, by 

 Fincke."® 



Of the presence of oxalic acid in leaves there exists very little doubt. 

 Franzen ^" and his collaborators have made a very careful critical examina- 

 tion of all the publications in which malic, citric, tartaric and succinic 

 acids are reported as constituents of plants. It is concluded that in a 

 relatively small percentage of cases is the evidence which has been pre- 

 sented to show the presence of these acids, sufficient to warrant the 

 conclusions. 



An interesting substance has been isolated by Curtius and Franzen ^^ 

 by the distillation with steam of macerated leaves. After removal of 

 the acids in the distillate, they were able to isolate a-(3-hexylene aldehyde, 

 CH3 . CH2 . CH, . CH : CH . CHO. This aldehyde gives many of the re- 

 actions of formaldehyde and in all probability in some cases it has been 



"Rouge, C. A., 15, 2294 (1921). 



"Brunner and Chuard, Ber. chem. Gcs., 19, 595 (1886). Lippmann, ibid., 24, 

 3299 (1891). Talladin, Bull. acad. sci. Petrograd (1916), 1021. 



" Gorup-Besanez, Ann. Chcin., 161, 229 (1872). Shorey, Jour. Am. Chem. Soc, 

 21, 45 (1899). Stolle, Chem-. Zcnt. (1900), II, 343. Ordonneau, Bull. soc. Chim. 

 (3), 6, 261 (1891). 



''Bergmann, Bat. Zeitg., 40, 731 (1882). 



™Fincke, Biochcm. Zeit., 51, 253 (1913) ; Unicrs. Nahr. Genussm., 27, 10 (1914). 



*" Franzen and Keyssner, Biochcm. Zeit., 135, 183 (1923). Franzen and Helwert, 

 ibid., 135, 384 (1923); 136, 291 (1923). Franzen and Ostertag, ibid., 136, 327 

 (1923). 



** Curtius and Franzen, Ann. Chem., 404, 93 (1914). 



