33 



travel in equal proportions to the root, where they are reformed into 

 saccharose. Where the rotatory power seems to suggest a difference 

 in amount of the two sugars, it is shown that other optically active 

 substances are present which might account for the results obtained. 



XX. " Studies of the Formation and Translocation of Carbohydrates 



in Plants." 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. Sawyer. 

 Journal of Agricultural Science, 1916. 7, 352-384. 



The potato leaf differs from the mangold leaf in that it contains 

 considerable quantities of starch. Previous investigators had found 

 maltose also, but the authors could not. They attributed the dis- 

 crepancy to the circumstance that in other investigations the leaves 

 had been dried prior to analysis, and during this process the enzyme 

 diastase had continued to form maltose, but the enzyme maltase, 

 which in the living leaf breaks down the maltose, had been destroyed, 

 thus causing an accum.ulation of maltose in the tissues. Instead of 

 drying the leaf they dropped it into boiling alcohol containing a little 

 ammonia, thereby destroying all enzymes and putting an end to further 

 action ; in these circumstances analysis gives a faithful representation 

 of the substance in the living leaf. 



The general results clearly resemble those obtained with the 

 mangold leaf. Saccharose is greatly in excess of the hexoses in the leaf, 

 but not in the stalks. All the evidence indicates that saccharose is 

 the sugar first formed in the mesophyll tissue ; it is then broken down 

 in the veins, midribs, and stalks, and reaches the tubers in the form of 

 hexoses ; there it is built up into starch. In the leaf any excess of 

 sugar is converted temporarily into starch, and reconverted into sugar 

 when necessary. 



As in the case of the mangold accurate values could not be obtained 

 for dextrose and laevulose individually, owing to the presence of optically 

 active impurities which are not removed by lead acetate ; the sum 

 of these two sugars was readily determined. 



XXI. " The Estimation of Carbohydrates." IV. — " The Supposed 

 Precipitation of Reducing Sugars by Basic Lead Acetate." 

 W. A. Davis. Journal of Agricultural Science, 1916. 8, 7-i5- 



Previous workers have found that loss of laevulose occurs when 

 basic lead acetate is added to a solution containing a mixture of sugars, 

 and have generally supposed that precipitation occurred. The author 

 finds that the decomposition of laevulose undoubtedly occurs when 

 the lead acetate acts fcr a long time, but not otherwise. There is no 

 precipitation, but the laevulose is transformed into another sugar, 

 apparently Lobry de Bruyn's giutose, which is optically nearly inactive 

 and has only half the reducing power of dextrose. 



XXII. "The Distribution of Maltase in plants." I. — "The Func- 

 tions of Maltase in Starch Degradation and its Influence 

 on the Amyloclastic Activity of the Plant Materials." 

 W. A. Davis. Biochemical Journal, 1916. 10, 31-48. 



Some 500 analyses of the sugars of leaves have been made in the 

 laboratory, but in no case could maltose be detected. Many different 



