164 MEDICINAL AND POISONOUS PLANTS 



arabin into a kind of glucose sugar known as arabinose. A 

 similar substance ^nelding arabinose forms about half of 

 gum tragacanth, about one-third of the gum being a carbo- 

 hydrate called tragacanthin (CcHioOj) which differs from 

 arabin in being insoluble, although it absorbs water and 

 swells exceedingly. Tragacanth is an exudation from wounds 

 made in the stems of the gum-bearing tragacanth shrub 



f n 





Fiu. 156. — Gum Arabic Tree {Amcia Souc/al, Pulse P'amily, Lcyuminosw). 

 A, flowering branch. B, flower. C, pod, half, showing seeds. D, seed, 

 cut between the seed-leaves to show seed-stem and seed-bud. E, seed, 

 cut across. (Taubert.) — A tree about 6 m. tall; bark gray; leaves 

 grayish; flowers yellow; pod yellowish. Native home, tropical Africa. 

 This tree yields the best gum ; several other species produce an inferior 

 quality. 



(Fig. 157) and related species. The root of the marshmallow 

 (Fig. 158) contains about one-third of its weight of a mucilage, 

 having the same formula as tragacanthin. The same formula 

 is given also to the mucilage yielded copiously by the outer 

 coat of the flaxseed (Fig. 279). A similar mucilage but with 

 the formula CisH.2sOi4 is obtained in large quantities from 

 the outer coat of quince seed (Fig. 93). The slipperiness of 



