STUDIES OF THE FORMATION AND TRANSLOCA- 

 TION 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. 



By WILLIAM A. DAVIS and GEORGE CONWORTH SAWYERS. 



(Rothamsted Experimental Station.) 



In the first two papers of this series (pp. 255-351) we have dealt with 

 the carbohydrates of the mangold, a plant which, Hke its near relation the 

 sugar beet, stores onh* saccharose in its root. One of the most striking 

 features of this plant is that it forms no starch in the leaf, except during 

 the very earliest stages of growth when it is a seedUng; it is only 

 during this period, when the root is very small and has not developed 

 sufhciently to store the sugars formed, that starch appears in the leaf at 

 all. When the mangold has begun to develop a large storage reservoir 

 in the root and the sugar can be readily translocated away so that 

 all danger is avoided of too high a concentration in the leaf, starch 

 ceases to be produced, and during the whole of the growth in August, 

 September, and until the roots are lifted at the end of October, it is 

 entirely absent from the leaf. Maltose too is entirely absent. In 

 these respects the mangold, although a dicotyledon, resembles mono- 

 cotyledonous plants such as the onion (Allium cepa) and snowdrop 

 (Galanthus nivaUf:), which do not form starch in the leaf although they 

 store both starch and inulin in the bulb; in many respects, as we have 

 shown, the phenomena of formation and translocation of sugars in 

 the mangold are similar to those observed by Parkin []i)l"2] in the 



' Mr A. J. Daish, who shared our earlier work, would have taken ])art in this investi- 

 gation had not his niilitaiy duties, after the outbreak of war, render(>d it impossible. 

 He assisted us during the heavy work of the 24 Imurs jjicking of July ll)-17tli, 1!II4, 

 and we wish here duly to acknowledge this. 



