W. A. Davis, A. J. Daish and Gr. C. Sawyer 257 



Brown and Morris from their study of the TrojJceolum leaf were able 

 to bring forward much evidence for the rejection of Sachs' view that all 

 the carbohydrate formed in photosynthesis passes through the starch 

 stage. The facts they adduce are more in accord with the idea put 

 forward by Meyer in 1886 that starch is only produced when the supj^ly of 

 formative carbohydrates is in excess of the metaboUc and translocating 

 powers of the cell in which they are contained. Starch begins to be 

 stored in the leaf when the concentration becomes too great for the 

 normal requirements of the cell ; the sepai'ation of the sugar as starch, 

 that is in an insoluble form, reheves this concentration. The subse- 

 quent dissolution of the starch at night was shown by Brown and 

 Morris to be brought about by an enzjnne similar in its nature to the 

 diastase of barley. All the plant leaves tested which form starch 

 were shown to contain such an enzyme. Brown and Morris proved, 

 moreover, that leaf diastase acts upon solid starch and that the amount 

 of diastase in the leaves increases with the time that the leaf has been 

 in darkness ; this is not due to the fact that it accumulates as the starch 

 disappears, owing to a diminished call upon it, but probably on account 

 of diastase being produced as a starvation phenomenon. In accordance 

 with the view that the starch is broken down by diastase, they give 

 analyses showing the presence of maltose in oven-dried Tropceolum 

 leaf. From similar material they isolated an osazone which, from an 

 analysis and melting point, ajDpeared to be identical with maltosazone. 

 Maltose was regarded as a normal constituent of foliage leaves formed 

 as a degradation product from the starch. 



One of the most novel conclusions drawn by Brown and Morris was 

 with regard to cane sugar. This was found to be present in even larger 

 proportions than starch and the way in which it fluctuated in the leaf 

 suggested that it was the first sugar formed in photosynthesis. Dextrose 

 and laevulose were also present and were more readily accounted for as 

 products of the hydrolysis of the cane sugar than as its precursors. 

 Since laevulose was generally in excess of dextrose it was suggested 

 that the latter is more quickly used up in respiration than the laevulose ; 

 therefore it seemed probable that under natural conditions a larger 

 amoimt of laevulose than of dextrose passes out of the leaf into the 

 stem in a given time. 



In 1884 A. Girard^ [1884] had also suggested that the saccharose 



1 Girard gives a valuable summary of the investigations prioi to 1884, dealing with 

 the special problem of the formation and transmission of sugar in the sugar beet. In 

 1883 Kayser [1883] had found, by analysis, both cane sugar and reducing sugar in the 



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