14 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



then formed there from the two hexoses. Furthermore, 

 when leaves have been kept in the dark till depleted of all 

 their starch, on exposure to light it is again formed in the 

 chloroplasts before sucrose appears. Maltose occurs only 

 in the leaf petiole, along with glucose, fructose, and sucrose. 

 The latter is the most important, and travels to the root, 

 where it is stored. The transformation of the hexose 

 sugars into sucrose takes place in the light, and ceases 

 when the leaf is placed in the dark. This, it may be 

 remarked, is probably rather an effect of the cessation of 

 the production and accumulation of glucose than of the 

 action of light as a protoplasmic stimulus. 



The above conclusions as to glucose being the first sugar 

 of photosynthesis are confirmed by a few quantitative 

 estimations of the sugars. An extract of the mesophyll, 

 from which even the finest veins had been excluded, was 

 found to contain O154 per cent, of dextrose, but only 

 O025 per cent, of sucrose, the latter probably being derived 

 from very fine veins which had been overlooked. On the 

 other hand, an extract of the veins with some of the 

 mesophyll lying between them contained O118 per cent, 

 of glucose and fructose combined together with 0'538 per 

 cent, of sucrose. Thus, the results obtained by Strakosch 

 are quite opposed to the conclusion of Brown and Morris, 

 that sucrose is the first sugar of photosynthesis. 



The glucose theory received further support from the 

 researches of Robertson, Irvine, and Dobson (1909), on the 

 sucroclastic enzymes of Beta vulgaris, from whose paper 

 Table VI. is quoted. 



It is noteworthy that invertase is absent from the beet- 

 root, in which sucrose is stored. Kastle and Clark (1903), 

 however, demonstrated its presence in the potato and 

 artichoke, where starch and mulih respectively form the 

 major part of the carbohydrate reserves. Diastase and 



