THE CARBOHYDRATES* OF THE ANGIOSPERM LEAF 33 



that formed from the hexoses in falling to their night 

 level. These two views are diametrically opposite to each 

 other, but it is clear that the first involves the direct trans- 

 formation of some hexose into starch, and regards sucrose 

 either as a temporary reserve or transport sugar. The 

 second looks upon sucrose as the primary sugar on the 

 direct road to starch, or, if not the primary, at any rate as 

 an indispensable prerequisite of starch formation. The 

 former view is practically that of Strakosch. The apparent 

 increase in the total carbon after darkness seems to be due 

 to the material having an unusually high starch content 

 through want of uniformity in the samples. 



The behaviour of maltose, which increases as starch 

 decreases, is entirely in agreement with the view of Brown 

 and Morris, that it is a down-grade product of starch. 



REVIEW OF RESULTS OF RESEARCHES ON THE MANGOLD. 

 On the whole Campbell's researches indicate that hexoses 

 are formed before sucrose, and soon attain a maximum. 

 Then sucrose increases, and, after reaching a certain limiting 

 value, begins to be transformed into starch. This agrees 

 with Strakosch's theory in regarding a hexose as the 

 primary sugar of photosynthesis, but regards sucrose as a 

 necessary stage in starch formation. The latter appears 

 to the present writer to be an unwarranted conclusion, as 

 the limiting concentration attained to by the sucrose may 

 be readily explained as due to its rapid translocation. The 

 ease with which darkened leaves form starch when supplied 

 with nutrient solutions of various sugars suggests that 

 starch may be formed directly from different sugars in 

 different species of plants. It has, however, been empha- 

 sized by Lundegardh (1914) that the system Sugar ^ > 

 Starch is not a simple reversible reaction governed by the 

 laws of mass action; for increase of the sugar content of the 



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