370 H. A. SPOEHR 



out however a definite solution having ioeen reached. There is 

 no doubt, however, that starch contains varying quantities of 

 pentoses. This is a fact'' which apparently has been disregarded 

 in most of the studies on the constitution of starch, but which 

 certainly must be of greatest importance in the study of the 

 metabolic relations of starch and the other carbohydrates. 



The question then naturally arises; is starch really of fixed 

 constitution or is it rather of a heterogeneous nature? Un- 

 doubtedly glucose predominates in its products of hydrolysis. 

 But glucose usually also is present in largest amounts in the 

 plant juices, it does not seem unreasonable to suppose therefore 

 that when the carbohydrates are laid down this sugar should 

 predominate. Could it be that starch is a form (a physical form) 

 in which the various sugars are laid down for storage and that 

 the pentoses should be included herein? If this were so it could 

 be expected that any of the sugars when presented to a starch- 

 free leaf would produce starch therein. It has been shown that 

 this is the case with all the fermentable sugars. Cremer and 

 Bokorny got doubtful results with 1-arabinose and 1-xylose. 



The writer placed leaves of Ampelopsis quinquefolia which had 

 lost all their starch (by being kept in the dark) on solutions of 

 1% and 2% pure 1-arabinose (m.p. 160°) in distilled water. 

 After having been kept in these solutions for two days in the 

 dark, the chorophyll was dissolved out by means of hot 80% 

 alcohol, and the leaves were tested for starch with alcoholic io- 

 dine and with chloralhydrate and iodine. The results were un- 

 mistakable; along the main veins and 1 to 2 mm. to either side, 

 the dark blue color of the starch-iodine was visible. 



Of course, from this experiment it cannot be concluded defi- 

 nitely that the 1-arabinose went directly to form starch in the 

 leaf, for there are other substances (e.g., glycerine) which also 

 form starch in the leaf, and we are certain that these are not 

 directly appropriated. In view of the foregoing, however, the 

 experiment is suggestive, and does indicate that this sugar is 



« Winterstein, E., Ber. d. deutsch. Chem. Ges. 25: 1237-12-11, 1892. 

 Lintner, C. J., Zeit. angw. Chem. 11: 725-729, 1898. Chem. Zentr. 62: II, 

 732, 1891. 



