W. A. Davis 



349 



to i p.m. theu falls until 11 p.m., when a second rise occurs. In the 

 mid-ribs (Fig. 10 of preceding paper) the reverse is the case, the dextrose 

 being nearly constant during the day and faUing at night, whilst the 

 laevulose falls by day and increases by night. 



Table IX. 



Divergence of Results for Saccharose in Stalks by Polarisation Method. 

 Series II. September lOth-llth, 1912. 



Summary. 



1. It is shown that in the extracts of mangold leaves and stalks 

 optically active impurities are always present which are not precipitated 

 by basic lead acetate and hence vitiate the estimation of the dextrose 

 and laevulose. These substances are possibly acid amides (such as 

 glutamine and asparagine) or amino-acids (such as glutamic and aspartic 

 acids) which form soluble lead salts. 



2. These impurities occur in the leaves, but are much more abundant 

 in the mid-ribs and stalks. 



3. In the leaves the dextrose and laevulose appear to be present 

 in approximately equal amount, as would be expected if they were 



formed from saccharose by inversion. When the ratio y departs from 



unity it is probably owing to the presence of a dextro-rotatory impurity 

 (glutamine?) which increases the amount of dextrose apparently 

 present ; but at certain times of the day a laevo-rotatory impurity 



seems to predominate so that the ratio y becomes less than unity. 



