:)70 GarhoJujdrates of thr Leaf of the Pofofo 



hexoses rise so does the rotation of the aqueous extract and when the 

 hoxoscs fall abruptly, as between 8 and 10 a.m., when the starch increases, 

 the rotation also falls very greatly. From 10 a.m. to 2 p.m. the general 

 character of the hexose and rotation curves is similar as regards rise and 

 fall ; from 2 p.m. onwards, when the cane sugar falls and the hexoses 

 increase, there is a rapid rise of the rotation curve, which seems to follow 

 more or less the formation of "soluble starch'" and starch. The 

 rotation curve reaches a maximum at the same time ((J ]).iii.) as the 

 hexoses, soluble starch and true starch, and then falls abruptly, just 

 as the starch curves fall, between (5 p.m. and 8 p.m. At night the 

 rotation curve follows, on an exaggerated scale, the curve of hexoses 

 and is the inverse of the starch curve. 



The intimate relation existing between the three curves under 

 discussion, which show the variation of the hexoses, starch and rotation 

 of the aqueous extract of the sugar-free leaf, points to the starch and 

 hexoses being readily interconvertible. The substance with high 

 positive rotatory power which appears so intimately related to the starch 

 and hexoses may either be an intermediate product in the synthesis of 

 starch (other than dextrin or soluble starch) or a substance such as a 

 protein or gum, with a high positive rotation, which stands in close 

 causal relationship with this synthesis. In the present state of our 

 knowledge it is useless to offer further conjectures. 



B. The Stalks and the Translocation of the Sugars. 



As in the mangold stalks, the saccharose remains practically constant 

 in the potato stalk throughout the day (3-2 to 3-6 per cent.) in spite of 

 a much larger variation of this sugar in the leaf (see Fig. 2). At night a 

 slight fall occurs followed by an increase after sunrise to nearly the former 

 level. The hexoses vary in somewhat the same way, but the range of 

 variation is greater during the day (4-94 to 5-63) and the fall at night 

 correspondingly la rger [fyG'i to f •(')■'?). The curve of apparent dextrose (for 

 data see Table V) is almost parallel to the saccharose curve and the same 

 is true of the curve of apparent Inevidnse; the dextrose, as in the man- 

 gold stalk, always appears to be in large excess as compared with the 



laevulose, the ratio , (pentoses as xylose) varying between (•.") and Tj-,"). 

 ij 



Although the laevulose and dextrose curves are practically parallel, the 

 absolute increases during the day being nearly the same, the value y 



