Chap, ii Photosynthesis 



3°7 



With the exception of this statement of Sachs, there 

 seems to be very little evidence, up to the early eighties, 

 that sugar exists in foliage leaves. 



After 1880 investigations into the nature of the carbo^ 

 hydrates of the leaf were numerous. In 1882 Miiller- 

 Thurgau showed that the amount of cupric-reducing sub- 

 stance in leaves increases in quantity in the leaf as the 

 starch diminishes. Kayser in the next year proved in 

 the leaves of several plants the presence of cane sugar 

 and the products of its inversion, obtaining the former 

 in a pure condition by crystallizing it from the cell 

 sap. In the paper of 1885, to which reference has 

 been made, Meyer gives the first proof of the existence 

 of reducing sugar in the leaf. Taking the expressed sap 

 of 20 kilos of the leaves of Allium porrum he precipitated 

 the sugar by ammonia and acetate of lead. He failed 

 to crystallize it but found it to yield an osazone melting 

 at 204 C. It had an optical activity a D -20°. He was 

 not able to identify it further, but its characteristics 

 agreed fairly closely with those of invert sugar. Meyer 

 could not prepare either glucose or levulose from it. In 

 1885 Schimper concluded that the formation of glucose 

 precedes that of starch in the leaf, the latter being 

 constructed from it when it has attained a certain con- 

 centration. Meyer found inulin in the leaves of Yucca. 

 In 1891 Keim detected cane sugar in the leaves of the 

 cherry. 



In 1892 Brown and Morris subjected the sugars of the 

 leaves of many plants to an exhaustive examination, in 

 the course of which they identified among them cane sugar, 

 maltose, glucose, and fructose. They came to the un- 

 expected conclusion that ' at any rate in the leaves of 

 Tropceolum cane sugar is the first sugar to be synthesized 

 by the assimilatory process '. Their opinion was based upon 

 quantitative determination of the amounts of the various 



u 2 



