228 SCIENCE PROGRESS 



collected in the field at two-hourly intervals throughout a 

 twenty-four hour day, at three different season of the growing 

 period (" Studies of the Formation and Translocation of Car- 

 bohydrates in Plants," I and II, Journ. Agric. Sci. 7, 255-326, 

 327-51, 1 9 16). For this work the methods of carbohydrate 

 estimation when a mixture of carbohydrates is concerned had 

 first to be worked out. This they succeeded in doing, and 

 analyses were made of starch, sucrose, maltose, glucose, fructose, 

 pentoses and pentosans. In some supplementary work with 

 potato (Studies III., Journ. Agric. Sci. 7, 352-84, 19 16) " soluble 

 starch " was estimated as well. The chief conclusion of these 

 workers is the same as that of Brown and Morris, in that they 

 regard sucrose as the primary sugar of carbon-assimilation from 

 which hexoses arise later for translocatory purposes. On the 

 other hand, they disagree with Brown and Morris in that they 

 find pentoses present in measurable amount, while maltose is 

 consistently absent from the leaves examined. Starch is never 

 present in the leaves of mangold, but occurs in large quantities 

 in potato leaves. 



Further results of Davis, Daish and Sawyer's researches are 

 that both sucrose and hexoses increase in quantity in the leaf 

 during the middle hours of the day, and then fall off in amount 

 during the night. As the season progresses the sugars increase 

 in amount, but the sucrose to a much greater extent than the 

 hexoses. 



A recent contribution by Gast (Hoppe-Seyler's Zeitsch. f. 

 physiol. Chem. 99, 1-53, 191 7) also attempts to repeat and 

 amplify Brown and Morris's observations. Gast's analytical 

 methods are somewhat similar to those of Davis, Daish and 

 Sawyer, but his conclusions are based on the analyses of the 

 leaves of five species collected early in the afternoon, and in 

 the early morning. His results completely confirm those of 

 Brown and Morris, even to the absence of pentoses and the 

 presence of maltose in leaves. He points out with much 

 justice that these results do not indicate that sucrose is the first 

 produced sugar in the leaf, but that a good case can be made 

 out for regarding cane-sugar as the first recognisable product of 

 assimilation. Thus in some cases (e.g. Cucurbita, Canna) no 

 glucose and very little fructose could be determined during the 

 day. 



In a critical and very important study by A. Ursprung 



