Carbohydrate Transformations in the Leaf. 127 



capacity for forming starch, many plants not forming it all. In tiiese 

 cases it was siiovvn tiiat tlie absence of starch was not due to rapid 

 translocation, for no starch was formed even under conditions most 

 favourable to rapid assimilation and accumulation of products. 

 The same investigator showed later (1886) that leaves depleted of 

 starch floated on sugar solutions could form starch from the sugars. 

 Thus almost all leaves formed starch from a 10% solution of fructose, 

 a few from glucose and a very few from galactose, It became 

 reasonable to suppose that starch might possibly be formed in the 

 leaf from sugar. 



Confirmatory evidence of this theory was derived from 

 researches on stai-ch formation in the plant, carried out by Boehm 

 (1874, 1876, 1877) and notably by Schimper (1880). Boehm showed 

 that starch in the leaf is not necessarily always the direct result of 

 carbon assimilation. Thus he showed the formation of starch in the 

 leaf as a result of transference of reserve material from other tissues 

 under feeble light intensity, and in an atmosphere devoid of carbon 

 dioxide. Schimper investigated the development of the starch granule. 

 He showed that starch is always formed in a plastid, which might be 

 colourless or green, and although he held that the mesophyll 

 chloroplasts could not elaborate starch from other carbohydrates, 

 further work of Boehm (1883) and that of A. Meyer mentioned above, 

 showed that these chloroplasts could elaborate staich from sugars. 

 These considerations lead to the conclusion that there is no difference 

 between the chloroplast and the colourless amyloplast in regard to 

 their powers of elaborating starch, and it is at least possible that 

 starch formed normally in the chloroplast is formed secondarily and 

 not as a direct result of assimilation. 



These considerations were generally held to support Baeyer's 

 suggestion, to which we shall refer in detail later, that the first part of 

 the assimilation process consisted in the formation of formaldehyde 

 which polymerised to hexose, and then gave rise to sucrose or starch. 

 This hypothesis, which involves the view of hexose as the first sugar 

 formed in assimilation, has recently received support from the work 

 of Strakosch (1907), who investigated the distribution of sugars in 

 the leaf and other parts of the sugar beet, by means of microchemical 

 tests depending on the production of osazones. He concludes 

 that glucose is the only sugar present in the mesophyll cells of the 

 leaf. In the veins fructose appears as well, and later, sucrose. 

 Maltose also occurs only in the petiole. Strakosch therefore 

 concludes that glucose is the first sugar formed in assimilation and 



