W. A. Davis and G. C, Sawyer :369 



to about 1-3 per cent., whilst the hexoses fall correspondingly. It is 

 noteworthy that the starch appears to be formed in early morning 

 considerably before the sugars show any increase. The slight increase 

 of starch after sunset, between 8 p.m. and 10 p.m., at the expense of the 

 hexoses is also very striking; at this time of day the intensity of the 

 light was small. 



Hexose-saccharose ratio. The curve showing the variation of this 

 ratio naturally follows in its general outline the hexose curve with its 

 abrupt changes. This is a consequence of the linear character of the 

 saccharose curve. 



Pentoses. These show a slight increase in the early part of the day, 

 but from noon onwards are practically constant. 



Pentosans and ^natter insoluble in alcohol. In the mangold leaf one 

 of the most striking features was the absolute parallelism of the curves 

 of jjentosans and of matter insoluble in alcohol. This parallelism is 

 almost entirely lost in the case of the potato leaf, apparently owing to 

 the presence of starch and its precursors. At night, in particular, the 

 pentosans appear to increase, whilst the matter insoluble in alcohol 

 (including the starch) diminishes. 



notation of the aqueous extract of the dried leaf tissue left after extracting 

 the sugars. The curve showing the variation of the rotation of the aqueous 

 extract of the dried leaf tissue from which all alcohol-soluble substances 

 have been removed is probably an index of the variation of synthetical 

 products intermediate between the hexoses and starch. Generally 

 speaking this curve is intermediate in its character between the starch 

 curve and the hexose curve. Table I shows that the rotation of this 

 extract calculated as soluble starch points to the presence of considerable 

 quantities of substances with a high positive rotation, which are possibly 

 of the nature of gums but more probably are up-grade or down-grade 

 products of starch, other than dextrin or soluble starch. They are 

 generally not convertible into hexose by taka-diastase ; it is only 

 between 4 p.m. and 8 p.m. that a small quantity of a substance which 

 is so convertible appears in the leaf. Even when this is present the 

 rotation of the aqueous extract is from 2i to 4 times that corresponding 

 with the "soluble starch" actually found. 



During the early part of the day up to 12 noon the curve of the 

 rotation, a^, is more or less parallel with the hexose curve^; as the 



^ It must be borne in mind that the two curves (hexose and rotation curves) apply 

 to different portions of the material analysed : the hexoses are estimated in the alcohol- 

 soluble extract, whilst the rotation curve refers to the aqueous extract of the material 

 left after all the substances soluble in alcohol have been removed. 



25—2 



