122 THE CARBOHYDRATES 



and barley. In its characters it closely resembles mannane, 

 and by some authors is regarded as identical with it ; when 

 dry, it is a spongy friable substance which swells upon the 

 addition of water. It is soluble in cold water and is optically 

 inactive. Its sugar is fermentable and non-crystalline. 



GALACTOSANES. 



GALACTANE. 



Exactly analogous to the mannanes are the galactanes, 

 which may be looked upon as anhydrides of galactose. They 

 occur in a great variety of different forms, some of which are 

 readily hydrolysed by warming with alkali, while others are 

 very resistant even towards boiling alkali. Four galactanes 

 have been described, which are distinguished by the prefixes 

 a-, yS-, y- and 8- ; they are all amorphous substances 

 which dissolve with difficulty in water, and on hydrolysis yield 

 galactose. 



PARAGALACTANE. 



Paragalactane is a substance which is better termed para- 

 gal act o-arabane, since on hydrolysis by weak mineral acids it 

 yields a mixture of galactose and arabinose. It occurs in the 

 cell walls of the cotyledons of many plants, e.g., Lupinus 

 luteus and other species, Phoenix dactylifera, Cocos nucifera, and 

 other palms, Soja hispanica and Coffea arabica, where it forms 

 a reserve food-material which is digested on germination. 



Paragalactane is a white solid which is insoluble in water 

 and cuprammonia; it dissolves in hot potash. On heating 

 with nitric acid it is oxidized to mucic acid. Microchemically 

 it may be identified by its insolubility in the reagents men- 

 tioned, and also by the fact that with phloroglucin and hydro- 

 chloric acid it gives a red coloration on warming. No colour 

 is given in the cold. 



Its association with cellulose prevents the latter exhibiting 

 some of its reactions ; thus the cellulose is unacted upon by 

 cuprammonia unless the paragalactane be removed ; this may 

 be done by boiling in dilute hydrochloric acid. 



