1 66 Carbon Asshnilation. 



t^ssHr.O^N.Mg + 200, + 2H,0 = Mg(HC03), + C,,H,^0,li,. 



chlorophyll a phaeophytin a 



but he finds more carbon dioxide is absorbed than can be accounted 

 for by these two processes. For example, 0-505 g. chlorophyll 

 (a + b) was used in 104-02 c.c. water. This absorbed 184-45 c.c. 

 carbon dioxide at 0°C and 747-3 mm. partial pressure, i.e., 6-45 c.c. 

 more than could be accounted for by the water. This is equivalent 

 to 12-6 mg. Of this 7 mg. would be used in the formation of 

 pheeophytin according to the equation given above ; there thus 

 remains 5-6 mg. unaccounted for. 



We do not see any necessity to introduce a mystical and purely 

 hypothetical peroxide in order to explain this result. Indeed, the 

 assumption of the formation of such a peroxide is purely gratuitous 

 in view of the fact that we have absolutely no information in regard 

 to the behaviour of carbon dioxide towards the ester groups of the 

 chlorophyll molecule.' 



From his experiments on the absorption of carbon dioxide in 

 the dark by living leaves and leaf powder, Willstatter concludes that 

 in the leaf there is a mechanism for absorbing carbon dioxide as 

 the leaves and leaf powder absorb many times as much carbon 

 dioxide as can be explained as due to absorption by the chlorophyll. 

 To explain this he puts forward exactly the same hypothesis that 

 Siegfried had propounded ten years before, without, however, 

 making any reference to Siegfried. It may be interesting to 

 compare with Siegfried's results already cited, the remark of 

 Willstatter (1915 b, p. 345) " It is possible that in the absorption 

 phenomenon described, carbamino compounds of amino acids or of 

 proteins are formed. Preparation work is here presented with a 

 new problem." This last sentence suggests that Willstatter is 

 unaware of Siegfried's work. 



' It is intei-estiiig to note that the solubility of carbon dioxide in some 

 alcohols and esters is much greater than in water, see e.g., Just (1901). 



