28 THE SYNTHESIS OF CARBOHYDRATES 



He even found starch to be formed on exposure to infra-red 

 rays ; it is, however, not clear whether this starch was a direct 

 product of carbon assimilation. Further investigation is 

 required on the relationship between carbon assimilation and 

 the specific wave lengths absorbed. Ursprung found in the 

 instance of Phalaris arundinacea var. picta^ which plant was 

 selected since its variegated leaves permit a comparison between 

 the green and non-green portions, that in the red region of the 

 spectrum the maximum absorption obtains between the B and 

 C lines, in the green the absorption is general, whilst in the 

 violet the absorption is greater than between the B and C lines 

 of the red, and beyond this there is a rapid fall. Subsequent 

 work on Phaseolus showed a sharp rise in the assimilation curve 

 from the outer limits of the red to a maximum situated near 

 the C line, from which point there is a gradual fall towards the 

 violet This curve does not correspond, more especially as 

 regards the region of shorter wave lengths, with the curve of 

 absorption which rises from E, in the green region, to the 

 violet. In view of the fact that carbon assimilation takes place 

 in this part of the spectrum, it is obvious that some new con- 

 ditioning factor is operative ; it is suggested that this is found 

 in the action of the 'violet rays causing the stomates partially 

 to close. 



The consideration of the absorption of energy leads to a 

 host of questions regarding the conversion of radiant into other 

 forms of energy, chemical and electrical. And here the realm 

 of hypothesis is reached, for there is no certain knowledge as to 

 the fate of the absorbed energy, the relative and absolute values 

 of specific radiations, and in what form it is dissipated. 



With regard to the ultra-violet rays, the more injurious of 

 which are absorbed by the atmosphere, and which in the light 

 of Ursprung's work assume a greater importance, Stoklasa and 

 Zdobnicky * brought about the synthesis of carbohydrate in the 

 absence of chlorophyll by passing light from a quartz mercury 

 lamp through a mica window into a vessel containing a mixture 

 of carbon dioxide and nascent hydrogen. 



Formaldehyde was slowly produced and this, in the presence 

 of caustic potash, was polymerized with the formation of a sugar 

 or a mixture of sugars which was optically inactive and not fer- 



* Stoklasa and Zdobnicky : " Chem. Zeit.," 1910, 945. 



