44 THE SYNTHESIS OF CARBOHYDRATES 



with extreme rapidity, for there is no evidence of its occurrence 

 as such in assimilating tissues, remarkable for a compound so 

 inert. The balance of evidence is against its use by the plant 

 when substituted for carbon dioxide. 



Formaldehyde. There is no doubt that formaldehyde can 

 be obtained from green leaves, there being many compounds 

 which yield it more or less readily on decomposition. The 

 production of formaldehyde in artificial chlorophyll systems 

 was once considered strongly to support Baeyer's hypothesis,* 

 but the work of Jorgensen and Kidd, who were the first to use 

 pure chlorophyll in this connexion, seriously discounts the 

 significance of the reactions since the formaldehyde has its 

 origin in the oxidation of the chlorophyll ; it is not produced in 

 such systems if oxygen be absent. Much of the evidence re- 

 lating to the production of formaldehyde from carbon dioxide 

 and water under the influence of radiant energy is contradictory. 

 The work of Baly and Heilbron, however, has placed this as- 

 pect of the subject on a much firmer basis. 



The facts relating to the production of formaldehyde in the 

 presence of catalysts, although of interest in themselves and 

 important in other connexions, provide no proof that such re- 

 actions obtain in the normal plant. 



The contention of Willstatter and Stoll based on the as- 

 similatory ratio is ingenious, but, since the formaldehyde was 

 not actually demonstrated, the evidence is not convincing. 



Formic Acid. As compared with formaldehyde the formic 

 acid hypothesis has received much less attention : Spoehr's 

 judgment appears to be just ; there is more in its favour than 

 for formaldehyde. 



Feeding Experiments. That plants under abnormal con- 

 ditions, deprived of their natural raw food materials, may 

 make use of other substances in the elaboration of their food 

 shows that the plant is a transcendental chemist and in virtue 

 of its powers can to a certain degree make use of the sub- 

 stitutes. The facts do not prove that these substitutes, for- 

 maldehyde and formic acid, are normal intermediate products 

 in the natural process. If, on the other hand, it is held that 



* See, for example, Usher and Priestley : " Proc. Roy. Soc.," Lond., B., 1906, 

 77, 369; 1906, 78, 318; 1911,84, 101. 



