382 Citrhohydrates of the Leaf of the Potato 



It is shown that the presence of these impurities also falsifies the results 

 obtained for saccharose by the double polarisation method. The 

 fluctuations of the "apparent dextrose"' and "apparent laevulose" in 

 the leaf really indicate variations in these impurities rather than 

 variations in the hexoses, which are perhaps present mainly as invert 

 sugar. In the stalks, where the amount of optically active impurity 

 appears to be less than in the leaves, it is possible that the dextrose is 

 actually in excess as it appears to be, and that the starch in the tuber 

 is built up from this sugar. 



7. Maltose is invariably absent from the potato leaf and also from 

 the leaves of other plants which form much starch in the leaf. The 

 degradation of starch in the leaves is probably effected by a mixture of 

 enzymes similar to the enzymes of AspergiUus nri/zae (taka-diastase) ; 

 maltase is always in relative excess, so that the starch is degraded 

 completely to dextrose. The series of changes is therefore: 



Starch -— dextrins — maltose ^- dextrose. 



Appendix. Experimental Data. 



Potato Leaves. July UJth-17th, 1914. 



In the first two analyses (6 a.m. and 8 a.m.), after the treatment 

 with basic lead acetate, the precipitate was washed to 2 litres, but the 

 first and second litre of washings were analysed separately so as to 

 obtain an idea of the amount of sugars left behind when the washing 

 was continued only to 1 litre. As it was found that this was quite 

 appreciable, in all the later analyses the lead precipitate was- washed 

 to nearly 2 litres, and after precipitation with sodium carbonate the 

 solution was made to 2000 cc. (= A). 



The extract of the leaf material was evaporated in vacuo and made 

 up to 500 cc. 440 cc. of the 500 were treated with basic lead acetate 

 and the precipitate washed to 1 litre ; the filtrate was treated with soHd 

 sodium carbonate and made to 1000 cc. = A. 



The second Utre of washings was also treated with solid sodium 

 carbonate and made up to 1000 cc. = A'. 



