1906.] Mechanism of Carbon Assimilation in Green Plants. 327 



identified, but there is indirect evidence of its formation at some stage. 

 Whilst hydrogen is always found among the products of the action of light 

 on carbon dioxide in the presence of uranium compounds, under no conditions 

 in any way approaching those of the experiments in question has hydrogen 

 been obtained from formic acid. The reduction of uranic oxide, or of 

 uranium peroxide, to a violet-coloured lower oxide, which was always 

 observed in the experiments with carbon dioxide, can again only be brought 

 about by formaldehyde ; whilst the formation of a substance with the 

 properties of methylenitan, which has only been prepared from formaldehyde, 

 furnishes additional support to this view. 



Summary. 



I. — (1) Photolytic decomposition of aqueous carbon dioxide can take place 

 in the presence of chlorophyll, independently of vital or enzymic activity, 

 provided that the necessary physical and chemical conditions are strictly 

 adhered to. 



(2) The products of the decomposition are formaldehyde and hydrogen 

 peroxide, formic acid being an intermediate product. 



(3) It is possible to reconstruct the process of photosynthesis outside the 

 green plant, (a) as far as the production of formaldehyde and oxygen, by 

 introducing a suitable catalysing enzyme into the system, and (b) as far as the 

 production of oxygen and starch, by introducing, in addition to the enzyme, 

 certain kinds of non-chlorophyllous living protoplasm. 



II. — (1) There is direct experimental proof that formic acid is a product 

 of the photolytic decomposition of carbon dioxide in the presence of an 

 inorganic uranium salt. 



(2) Formaldehyde has not been isolated and identified in the case of an 

 inorganic uranium salt, but a study of the reactions involved favours the 

 view that it is formed as a transitory intermediate product. 



