34 THE SYNTHESIS OF CARBOHYDRATES 



plant was selected since its variegated leaves permit a com- 

 parison 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 conditioning factor is operative ; 

 it is suggested that this is found in the action of the violet 

 rays causing the stomates partially to close. 



Lubimenko* found from controlled experiments that photo- 

 synthesis is more active in the red than in the blue rays ; it 

 is only in shade plants that the process is equally intense 

 in the two regions. Wurmser,"}" in his investigations on the 

 subject, used Ulva lactuca and from his measurements found 

 that the ratio of carbon assimilation to the amount of energy 

 absorbed was i-o for red light, 4-0 for green and 2-35 for violet 

 light, which means that the green rays although absorbed in 

 a much lesser degree are utilized four times more than the 

 red. From further investigations he found that Ulva has 

 a photosynthetic efficiency of 59 per cent, in red light and 

 83 per cent, in green light. The value obtained for the red 

 rays does not, he thinks, represent maximum efficiency. He 

 concludes that the efficiency is much the same for all wave- 

 lengths and lies between 70 and 80 per cent. 



Warburg and Negelein,{ in most carefully controlled ex- 



* Lubimenko : " Compt. rend.," 1923, 177, 606. 



f Wurmser : '" Recherches sur l'assimilation chlorophyllienne," Paris, 

 1921 ; " Bull. Soc. chim. biol.," 1923, 6, 487; *' Ann. Physiol. Physiochim. 

 Biol.," 1925, I, 47. 



J Warburg and Negelein : " Zeit. physikal. Chem.," 1922, 102, 235 ; 

 1923, 106, 191 ; " Naturwiss," 1922, 10, 647. 



