76 



THE CARBOHYDRATE ECONOMY OF CACTI. 



enough work has been done with the chlorophyllous leaf to draw valid con- 

 clusions, and this in turn has been due to the fact that the methods of sepa- 

 ration and determination have not been sufficiently delicate and accurate to 

 permit their application to such sensitive material. 



Chalmont, 1 Tollens/ and Windish and Hasse" come to the conclusion that 

 pentoses are formed from hexoses as first products of oxidation, that they 

 are relatively inert, and probably are of the nature of waste products. This 

 is based essentially upon their observations that the total pentosan-content of 

 seedlings, germinated and grown in the dark, increases with age. The 

 writer made determinations of the total pentoses in seedlings; the results 

 are quite the reverse, however. Wheat seeds were allowed to germinate on 

 glass wool in the dark; at intervals a number of seedlings were removed, 

 dried, ground, hydrolyzed with 1 per cent HC1, and after determining and 

 fermenting away the hexose sugars the pentose sugars were determined 

 (see table 39 ).' 



TABLE 39. Total hexose and pentose content of wheat seedlings. 



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 exist between closely related mem- 

 bers of either one of the groups. Many bacteria and molds are capable of 

 utilizing pentoses as the only source of carbon, while, on the other hand, 

 other organisms 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 

 yields : 



mg. 



d-fructose 523.7 



1-xylose 512.7 



d-galactose 489.3 



mg. 



d-glucose 477.1 



1-arabinose 350.0 



d-mannose . . 286.8 



1 CHALMONT, G. DE. Pentosans in plants, 1. (II) Amer. Chem. Jour., 16, 218-229, 

 589-611, 1894. 



. Die Bildung der Pentosane in den Pflanzen. Ber. d. deut. chem. Ges., 27, 



2722-2725, 1895. 



* TOLLENS, B. Ueber die Kohlehydrate des Maizes und der Gerste mit besond. 



Beruecksichtigung der Pentosane. Chem. Zentr., 69, II, 967-968, 1898. 

 8 WINDISH, W., and R. HASSE. Ueber den Pentosangehalt der Gerste und des Maizes, 

 inbesondere ueber das Verhalten der Pentosane bei der Keimung. Chem. 

 Zentr., 72, II, 1098-1099, 1901. 



* SPOEHB, H. A. The pentose sugars in plant metabolism. The Plant World, 20, 



365-379, 1917. 

 5 CZAPEK, F. Biochemie der Pflanzen: I. Page 311, 1913. Jena. 



