226 



The Photochemical Formation of Formaldehyde in 

 Green Plants. 



By S. B. ScHRYVER, D.Sc, Ph.D., Lecturer on Physiological Chemistry in 

 University College, London. 



(Communicated by Prof. E. H. Starling, F.R.S. Received November 13, 1909, — 



Read January 27, 1910.) 



Since von Baeyer propounded his theory of the formation of formic 

 aldehyde as an intermediate product in the synthesis of sugars from carbon 

 dioxide and water by green plants, many attempts have been made to 

 discover this substance, and to substantiate Baeyer's theory. The most 

 successful of these are due to Polacci,* and to Usher and Priestley.f More 

 recently E. J. Harvey Gibson, in conjunction with A. W. Titherley, has 

 adduced further evidence tending to show that formaldehyde is actually 

 formed in green plants, and the former has propounded a photo-electric theory 

 to account for the photochemical action.^ 



Nevertheless, the evidence liitherto brought forward has been generally 

 considered, from an experimental point of view, somewhat inconclusive, and 

 most of the above-quoted investigations have been subjected to numerous 

 criticisms. 



It is hardly necessary to examine these criticisms in detail here, nor to 

 discuss the various theories that have been advanced to explain the 

 mechanism of the reaction, § as it is thought that the experiments recorded in 

 this paper will support an alternative hypothesis, by means of which some 

 of the objections to the original conception of Baeyer may be removed. 



Method. 



During the course of some investigations on formaldehyde in foodstuffs|| 

 a method was devised, by means of wliich botli tlie free and combined 

 aldehyde could be readily detected and (luantitatively estimated, even 

 when the amount present did not exceed one part in a million. The 

 possession of this method afforded the opportunity for the re-investigation 

 of th(; vexed question of the pliotoclioiiiical synthesis of tlie aldehyde by 

 green phints. 



* 'Arch. Ital. Biolog.,' vol. ii"), p. 151, and vol. 37, p. 440. 

 + ' Roy. Soc. Proc.,' vol. 77, \>. 3G!), luiil vol. 78, p. 318. 

 \ 'Annals of Botany,' 1908, vol. 32, p. 117. 



§ See Polacci, ' Aocad. Liiiuci ilonia,' .June (i, 1908, ;iii(l ]<;\vai-l, ' Roy. Soc. Proc, 

 1908, vol. 80, p. 30. 



II Report No. 9, Innpector of FooiIh Deparlincnt of the Local (Jovornujcnt IJoanl. 



