126 EXPERIMENT STATION EECOED. [Vol.36 



leaf, midribs, and stalk. Saccharose exceeds hexoses somewhat in the very 

 young leaves, the reverse being true later in the season. In the midribs and 

 stalk, saccharose remains practically constant throughout the season, being 

 greatly exceeded by the hexoses, which show great diurnal and seasonal varia- 

 tion. During the daytime, the curve of the proportion of saccharose follows 

 the curve of the temperature, while the rise of the cun^e of hexoses exceeds 

 that of the curve of the temperature. 



The facts are thought to support the view that saccharose is the primary sugar 

 formed under the influence of chlorophyll in the leaf mesophyll. Before trans- 

 location, it is transformed into hexoses in the veins, midribs, and stalks, the 

 proportion of hexoses increasing as the material approaches the root which 

 it enters as hexose. It is there reconverted into saccharose, in which form it 

 can not leave the root until reconverted for use in the second season's growth. 

 It is considered improbable that the synthesis of hexoses to saccharose is 

 effected by invertase through a process of reversible zymo-hydrolysis, as in- 

 vertase is entirely absent from the root. Pentoses, which form only a small 

 proportion of the total sugars in the tissues, are thought to be formed from 

 hexoses and to be the precursors of the pentosans. 



II. The dcxtrose-lcvulose ratio in the mangold, W. A. Davis (pp. 327-351). — 

 In this work, it is said to have been found that in the extracts of mangold 

 leaves and stalks optically active impurities are always present which are 

 not precipitated by basic lead acetate and which hence vitiate the estimation 

 of dextrose and levulose. These substances are possibly acid amids or amino- 

 acids which form soluble lead salts, and occur much more abundantly in the 

 midribs and in the stalks than in the leaves. When the ratio of dextrose to 

 levulose is greater than unity (the value to be expected if they are formed into 

 saccharose by inversion), it is thought that the apparent dextrose present is 

 increased by the presence of a dextrorotatory impurity, possibly glutamin. 

 When the ratio is less than unity, as at certain times of day, a levorotatory 

 impurity is thought to predominate. In midribs and stalks, and especially near 

 the bases of the latter, the dextrose appears (probably on account of the im- 

 purity above mentioned) to exceed largely the levulose. Apparent fluctuations 

 in the ratio of dextrose to levulose are thought to be due to fluctuations in the 

 optically active impurities rather than in these sugars themselves. These 

 apparent fluctuations show some diurnal regularity. The presence of at least 

 two optically active substances at different hours is thought to be indicated. 

 It is provisionally held that the dextrose and levulose exist in the leaves and 

 stalks as invert sugar, and travel in nearly or exactly equal proportions to the 

 root, where retransformation into saccharose occurs. Wliich of these siigars 

 is the better adapted to tissue formation or to respiration is not considered as 

 settled by studies thus far reported. 



III. The carbohydrates of the leaf and leaf stalks of the potato. The 

 mechanism of the degradation of starch in the leaf, W. A. Davis and G. C. 

 t^awycr (pp. 852-384). — It is stated that in potato leaf the increase of sac- 

 charose, the principal sugar present when the tubers begin to develop, goes 

 on uniformly from sunrise to 2 p. m., following approximately the temperature 

 curve, but showing a steady decline during the rest of the 24 hours. 



Hexoses appear in the leaves in very small amounts, generally less than 1 

 per cent of their total dry weight. Fluctuations in their amount are explained 

 by their conversion into starch or the reverse change. Hexoses begin to in- 

 crease in the leaf as soon as saccharose has reached its maximum at 2 p. m., 

 presumably owing to hydrolysis of the saccharose to invert sugar. Dextrin, 

 appearing at the same hour, increases regularly to 6 p. m., when true starch 



