260 The Carhohydratex of the Mangold Leaf 



constant. Parkin's experiments were carried out with a plant, the 

 snowdrop, which in normal growth never elaborates starch, so that 

 complications which might arise from the presence of this carbohydrate 

 or of maltose (which was shown to be absent throughout) were avoided. 

 Parkin's view, which was also put forward by Brown and Morris in 

 1893, that the laevulose is present in excess of the glucose in the leaf — 

 pointing to the latter contributing more readily to the needs of the leaf 

 — is discussed in the next paper. 



Peklo [1908], who studied the localisation of sugars in the beet by 

 a microchemical method, concluded that the sieve-tubes of the phloem 

 contain the greatest amount of cane sugar; he considers that the 

 sieve-tubes serve mainly for the transit of the sugar and, after the 

 formation of callus plates, for the storage of sugar in the root. 



2. Reducing sugars (hexoses) held to he Oie ■primary products 

 and cane sugar to he formed from these. 



Maquenne [1895], in an attempt to explain the storage of .saccharose 

 in the beet, based on osmotic laws, stated that the osmotic pressure of 

 the leaf sap is practically identical with that of the root sap. As it is 

 essential to equilibrium that the concentration of the saccharose should 

 be double that of the invert sugar, when, owing to photosynthesis, 

 reducing sugars are formed in the leaf, they will travel to the root and 

 there take up the form of saccharose. 



Strakosch [1907] employing microchemical methods concluded that 

 dextrose is formed in the mesophyll of the leaf of Beta vulgaris and is 

 the only sugar found therein. The migration of dextrose into the leaf 

 veins is followed by the appearance of laevulose in these, and later by 

 the formation of saccharose. Strakosch considered that the cane sugar 

 must be regarded as a final product in the leaf and migrates to the root 

 as such. The amoimt of the monosaccharides in the leaf is not 

 appreciably altered by the migration of the saccharose to the root, 

 nor is it diminished when the leaves remain in the dark for some time. 

 Exposure of the leaves to light does not cause the saccharose to increase 

 beyond a certain maximum, which is attained in a short time. 



In 1909 Robertson, Irvine aiul Dobson [1909] studied the distri- 

 bution of enzymes in the roots, stalks and leaves of Beta i-^uJgaris ; 

 they showed that invertase is present in the leaf and stem but absent 

 from the root, and hence conclude that the cane sugar stored in the root 

 is formed from antecedent nujnosaccharides by reversible zymohy- 

 drolysis in the leaf and stem and is thence translocated as such. The 



