THE PRODUCTS OF PHOTOSYNTHESIS 219 



in the entire method of attempting to draw conclusions regarding the first 

 sugar formed in photosynthesis from analyses of leaves is that we have 

 not sufficient information concerning the transformations which the sugars 

 undergo independently of the photosynthetic process. We do know that 

 such changes take place, that temperature, intensity of illumination and 

 water-content afifect these transformations. The manner in which they 

 are brought about we are not as yet well informed on. It is clear that if 

 such changes occur while the leaf is being illuminated (and there is little 

 reason to suppose that they do not) the results of analyses may mean 

 nothing as to the sequence of formation of the sugars. For example, in 

 the experiments of Brown and Morris, it will be recalled that they regard 

 the accumulation of fructose as resulting from the hydrolysis of sucrose, 

 the equivalent quantity of glucose having been used in respiration. How 

 could the accumulation of fructose be explained, however, if we accepted 

 the idea of mutual conversion of glucose into fructose? That a conver- 

 sion of glucose into fructose and ince versa actually takes place in plants 

 there can be little doubt. We need but recall that when starch disappears 

 under conditions of wilting of the leaves, the starch is converted into 

 sucrose.^ ^° In leaves containing starch the sucrose content increases both 

 in the light and in the dark when water content of the leaves decreases. 

 From what we know of the chemistry of starch, this is a glucose anhydride. 

 In order that sucrose be formed from starch some of the glucose must be 

 converted into fructose. Similarly in the artichoke tuber inulin is trans- 

 formed into reducing sugars ; there is evidence that in the process there 

 is produced not only fructose, but glucose is apparently also formed. ^^^ 

 Inulin is a condensation product of fructose. If, in the hydrolysis of 

 inulin in the plant, glucose and fructose are formed, can it not be con- 

 cluded that the fructose has in part been converted into glucose? That 

 these two sugars can be converted into each other by means of caustic 

 alkalies, lead hydroxide and calcium hydroxide, has become evident from 

 the work of Lobry de Bruyn ^'" and van Ekenstein and of Nef : recently 

 Spoehr and Wilbur have shown that a similar mutual interconversion 

 takes place in solutions of disodium phosphate and in neutral mixtures of 

 this salt and sodium dihydrogen phosphate. In the mammalian body fruc- 

 tose is converted into glucose. ^^^ Whether a similar action takes place in 

 plants has not been demonstrated with certainty. 



The point which we wish to stress is that in a complex system such as 

 that with which we are dealing here, in which the synthesis and hydrolysis 

 of complex compounds are affected by a variety of conditions, the quantity 

 of any particular substance gives little information regarding the role of 

 that substance in a series of reactions. All of the carbohydrates, mono- 

 saccharides, disaccharides and starch are capable of conversion into each 



""Ahrens, Bot. Arch.. 5, 234 (1924). Tollenaar, Diss., Wageningen, 1925, p. 80. 

 "'Colin, Bull, assoc. cliim. sticr. dist., 37, 121 (1919). 



'"Lobry de Bruyn and van Ekenstein, Rec. trav. chim.. 14, 203 (1895) ; 15, 92 

 (1896) ; 16, 257 (1897). Nef, Ann. client., 376, 1 (1910) ; 403, 204 (1914). 

 ""Lusk, "The Science of Nutrition," 1917, p. 258. 



