PRODUCTS OF CARBON ASSIMILATION 53 



contain any sucrose, whilst Tilia europcza, a starch leaf, con- 

 tains much sucrose. 



These authors, together with others, conclude that sucrose 

 is the first sugar of photosynthesis, but, on the other hand, 

 there is evidence which may indicate that hexose, the sugar 

 required on current theoretical grounds, is the first sugar to 

 be formed, and various arguments have been formulated to 

 show that the results of the work outlined above really in- 

 dicate that hexose and not sucrose is the first sugar formed in 

 the photosynthetic process. 



Lepovsky and others * from their study on the sugars of 

 the sugar beet, conclude that reducing sugars are amongst the 

 first products of carbon assimilation. Weevers f compared 

 the nature of the sugars in the green and non-green parts of 

 a number of variegated leaves. In ten out of the twelve 

 examples examined, sucrose was the only sugar identified in 

 the non-green parts, whilst the green portions contained both 

 sucrose and glucose. Further, hexoses were the first sugars 

 to appear and then sucrose in the chlorophyllous parts of 

 these leaves on exposure to light after a period of darkness 

 sufficient to ensure depletion of carbohydrate. Invertase was 

 present both in the green and in the non-green regions, which 

 suggests that this enzyme by a reverse action condenses mono- 

 saccharides to disaccharide. Priestley, % in his review of the 

 evidence, points out that the sugars formed in the green leaf 

 are intermediate steps in the formation of more complex bodies, 

 such as polysaccharides and proteins, for the prompt formation 

 of which the intermediate steps must be rapidly accomplished. 

 Wherefore it is reasonable to conclude that the substances 

 formed in the intermediate stages, including the first sugar 

 of photosynthesis, would show but little change in their con- 

 centration ; they would not accumulate in the light and thus 

 would not show fluctuation in amount. In other words, the 

 fact that of the sugars of the green assimilating leaf, sucrose 

 shows the greatest fluctuation in amount during the day 



* Lepovsky, Schulz and Link : " Journ. Agric. Res.," 1926, 33, 59. 

 f Weevers : " Proc. Kon. Akad. Wetens., Amsterdam," 1923, 27, 1. 

 % Priestley : " New Phyt.," 1924, 23, 255. 



