PENTOSE SUGARS IN PLANT METABOLISM 



373 



HCl, and after determining and fermentating away the hexose 

 sugars the pentose sugars were determined (see table 1). 



Unquestionably many organisms utilize the pentose sugars as 

 sources of energy. In their physiological effects the differences 

 between the pentoses and hexoses are in many cases less than 



TABLE 1 



Dry weight 



Total hexose sugar < ^^ 



[Dry.. 



Total pentoses < ^^ 



IDry 



21.40 

 9.95 



46.50 

 0.26 

 0.05 



exist between closely related members of either one of the groups. 

 Many bacteria and molds are capable of utihzing pentoses as 

 the only source of carbon while on the other hand, other organ- 

 isms are quite incapable of doing so. The difference in food 

 value of the various hexoses are well known. 



Czapek^- gives the following values for Aspergillus niger in 

 weight of jdelds: 



mg?n. 



d-fructose 523 . 7 



1-Xylose 512.7 



d-Galactose 489.3 



mgm. 



d-Glucose 477 . 1 



1-arabinose 350.0 



d-Mannose 286.8 



The high nutritive value of 1-xylose is quite evident, while on 

 the other hand it is well known that the yeasts are quite incapable 

 of utilizing any of the pentose sugars. At the same time it must 

 be remembered that no one of the sugars is universally good 

 nutrient material. For example, as Winogradsky and Omlian- 

 ski^^ have show^n even d-glucose is borne only in very low con- 

 centrations by certain nitrate bacteria, and in this connection 

 the recent investigations of Knudson^* are of great interest. 



12 Czapek, F., Biochemie der Pflanzen, I, p. 311, Jena, 1913. 



13 Winogradsky and Omlianski, Zentr. f. Bakt., 1899, II, 329-344. 

 >* Knudson, L., Cornell Univ. Agr. Expt. Sta. Mem. 9: 1-57, 1916. 



