W. A. Davis, A. J. Daish and (i. C. Sawyer 307 



dry weight. Ou analogy with our results these lower portions of leaf 

 correspond with the extreme lower parts of the mangold leaf-stalks, 

 and would probably, if an analysis were made, be found to contain 

 practically the whole of the sugar in the form of reducing sugar. 



In the potato (see pp. 367-373), where saccharose is the predomi- 

 nating sugar in the leaf, the proportion of hexose in the stalks bearing 

 the leaflets is far higher than in these leaflets (5 to 30 fold) whilst the 

 saccharose is very nearly the same in both. 



TT ■ o 1 ■ Ratio ^-^ in 



Hexoses in baccharose m c.s. 



Stalk Leaflets Stalk Leaflets Stalk Leaflets 

 Minimum ... 4-G3 0-15 2-65 1-76 0-10 1-54 



Maximum ... 5-fi3 1-27 3-58 3-66 0-44 1-77 



It would seem, therefore, that in all plants of which a systetnatic 

 examination has been made (mangold, sugar beet, potato, snowdrop, 

 grape vine, dahlia, etc.) saccharose is formed directly in the mesophyll of 

 the leaf, whence it passes into the reins, mid-ribs and stallis, undergoing 

 more and inore complete inversion in its passage. The regulating 

 mechanism is apparently such that a nearly constant concentration of 

 cane sugar is maintained throughout the day and throughout the season 

 in the mid-ribs and stalks, whilst the reducing sugars vary within very 

 wide hmits. 



At first sight it would appear to be a clumsy and unnecessary 

 contrivance for plants such as the mangold and sugar beet to form cane 

 sugar in the leaf, then to transform it completely into hexoses in the 

 stalks only to have to reconvert it back again into cane sugar in the 

 roots ; it would seem to be a simpler arrangement for the cane sugar to 

 travel as such to the roots. As will be seen from the historical intro- 

 duction given on pp. 255-262, most workers in this field have assumed 

 this to be the case. It is a striking fact that even Girard's [1884] data 

 show an enormous preponderance of the hexoses over the saccharose 

 in the leaf-stalks of the sugar-beet (the hexoses being 5 to 10 times the 

 cane sugar, which generally was small) ; but he was apparently so struck 

 by the novel observation of the relatively large proportion of cane 

 sugar in the leaf, that he quite ignored the significance of the stalk 

 analyses, concluding that the saccharose passed tout forme from the leaf 

 to the root. 



It is probable however that the actual mechanism of storage adopted 

 possesses certain well-defined advantages ; in the first place, if the sugars 

 travel by simple diffusion, as has frequently been assumed, the rate of 



