W. A. Davis 



337 



that at these times the proportion of the sugars is greatest, so that 

 the effect of the rotation of the optically active impurity in falsifying 

 the results is least marked. At night, apparently, an excess of this 

 impurity is hberated, possibly as a waste product of metabolism, 

 owing to degradation changes predominating, so that the laevulose 

 appears to have disappeared entirely at 6 a.m., and a relatively large 

 'positive rotation remains unaccounted for even when the whole of the 

 reducing sugar is assumed to be dextrose. 



Fig. 1 shows the variation of "apparent dextrose" and "apparent 

 laevulose" on the assumption that the pentoses are xylose^ during 

 the 24 hours, August 26th-27th. Throughout this period the dextrose 



Fig. 1. Mangold leaves, apparent dextrose and laevulose, Series I, Aug. 26-27, 1913 



(pentose as .xylose). 



curve is above the laevulose ; during the period of actual insolation 

 the curves are approximately parallel to each other and to the saccharose 

 curve. If it were not for the presence of the dextro-rotatory impurity, 

 the two curves would probably nearly coincide — the dextrose curve 

 being lowered and the laevulose curve being correspondingly raised. 

 On the assumption that the pentose is arabinose, the two curves actually 

 coincide without any such correction being made. The parallehsm of 

 the curves of dextrose and laevulose with that of cane sugar is particu- 

 larly striking when the apparent steepness of the curve of total hexoses 

 is taken into account (see previous paper. Fig. 4), from which it might 



1 Throughout this paper the curves of dextrose and laevulose are drawn only for the 

 case when the pentose is assumed to be xylose. The curves obtained by assuming the 

 pentose to be arabinose are strictly parallel to these curves but slightly higher or lower ; 

 the effect of taking the pentose as arabinose instead of xylose is to raise the laevulose 

 curve and lower the dextrose curve. 



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