THE PRODUCTS OF PHOTOSYNTHESIS 205 



concentration of monosaccharides increases to a certain point conditions 

 are favorable for the formation of di- and polysaccharides. But the con- 

 version of monosaccharides into conjugated carbohydrates is also influenced 

 by other conditions such as temperature and water content. These re- 

 actions are reversible, so that under certain conditions the conjugated 

 carbohydrates in turn are again converted into monosaccharides. Since 

 the development of a plant represents an accumulation of potential energy, 

 there is usually a total net gain of carbohydrates vv^hich is in the form of 

 conjugated carbohydrates, composing the structural elements of the plant 

 and deposited in storage organs such as seeds, fruits, tubers, etc. We 

 shall here concern ourselves less with the contents of these latter organs, 

 but rather with those organs in which photosynthesis is taking place, more 

 particularly the leaves. 



Besides the monosaccharides, already mentioned, there are found in 

 leaves sucrose, maltose, dextrine, starch, i>entosans and cellulose. As we 

 are primarily interested in the more immediate products of photosynthesis, 

 the cellulose content is a matter of secondary consideration. Similarly 

 other conjugated saccharides have been found in plants, for instance, 

 trehalose, raffinose and melicitose, but their presence in leaves is question- 

 able and we have no evidence, consequently, that they need be considered 

 in a discussion of the primary products of photosynthesis. 



Sucrose. Conclusions as to the presence of sucrose in leaves are 

 largely based upon indirect determinations, usually the increase in reduc- 

 ing power and the change in optical rotation after inversion. Using these 

 methods, amounts ranging from 0.5 to 10 per cent of the dry leaf material 

 have been reported. The direct determination and isolation of sucrose is 

 associated with greater difficulties. Attempts to isolate sucrose by means 

 of the strontium compound and the calcium saccharate have been only 

 partially successful and have yielded conflicting results.^* 



Sucrose is usually identified through the following properties : it does 

 not reduce cuproalkaline solutions, and has a strong dextro rotation. 

 On inversion with acids or invertin sucrose is split into d-glucose and 

 d- fructose and the resulting mixture turns the plane of polarized light 

 to the left and also reduces cuproalkaline solutions. From the inverted 

 mixture the fructosemethylphenylosazone can be obtained and the presence 

 of glucose can be established by means of the saccharic acid reaction. 



Maltose, a disaccharide, composed of two molecules of d-glucose is a 

 familiar product of the hydrolysis of starch. It reduces cuproalkaline 

 solutions and is hydrolyzed into two molecules of d-glucose by acids and 

 by the enzyme maltase. 



The presence of this sugar normally in leaves has been a matter of 

 controversy. Brown and Morris *^^ maintain that a considerable portion 



•'Kayser, Land. Versuchs., 29, 465 (1883). Peligot, Ann. Chim. (3), 54, Z77 

 (1858). Schulze, Land. Versuchs.. 34, 403 (1887) ; Ber. chcm. Gcs., 21, 299 (1888) ; 

 Zeif. physiol. Chcm., 52, 404 (1907). Deleano, ibid., 80, 82 (1912). 



** Brown and Morris, Jour. Chem. Soc, 63, 667 (1893). Ruhland, Jahrb. unss. 

 Bot., 50, 200 (1911). Campbell, Jour. Agri. Sci., 4, 248 (1912). 



