369 



A Study of the Mechanism of Carbon Assimilation in Green 



Plants. 



By Francis L. Usher and J. H. Priestley, B.Sc, Lecturer in Botany at 

 University College, Bristol. 



(Communicated by Professor M. W. Travers, F.R.S. Received December 16, 

 1905,— Read January 18, 1906.) 



(From the Chemical and Botanical Departments, University College, Bristol.) 



Introduction. — The investigation to be described in this paper has had for 

 its object the elucidation of certain problems concerning the nature of the 

 first stages in the assimilation of carbon from carbon dioxide by the green 

 parts of plants ; and although far from complete, it has been thought 

 advisable to publish the results already obtained, inasmuch as the weather is 

 likely to hinder the experimental work for some time to come. 



In 1870 Baeyer put forward the hypothesis that formic aldehyde is the 

 first product of the decomposition of carbon dioxide in the plant. This 

 suggestion received some support from Bokorny,* who proved in 1891 that 

 starch was formed in the dark by the green filaments of Spirogyra when 

 immersed in a solution of sodium oxymethyl-sulphonate of - l to 1 per cent, 

 strength. 



Bokorny's experiments are possibly open to the objection that formaldehyde 

 condenses very readily to non-poisonous carbohydrates in presence of sulphites 

 or bisulphites, and it has been shown by Laurent and Actonf that starch is 

 formed in the dark from most sugars. 



Quite recently, Bouilhac and Tr^bouxJ have succeeded in growing plants 

 in a very dilute solution of pure formaldehyde. Treboux has found that 

 Modea forms starch in the dark from a 0'001-per-cent. solution of formal- 

 dehyde, and Bouilhac has shown that this is also the case with Sinapis alba 

 and some Algce. Their experiments bring out in a striking manner the 

 intensely poisonous nature of even very dilute solutions of formaldehyde. 



Evidence of this kind, however, is quite indirect, and on this account greater 

 importance attaches to the results obtained by Bach,§ who for the first time 

 demonstrated the decomposition of carbon dioxide by light outside the plant. 

 He showed that by passing pure carbon dioxide through a 1'5-per-cent. 



* ' Berichte,' 1891, vol. 24, p. 103. 



t ' Boy. Soe. Broc.,' 1890, vol. 47, p. 150. 



% ' Flora,' 1903, p. 73. 



§ ' Comptes Bendus,' 1893, vol. 116, p. 1145. 



