1644 MEDICINAL AND POISONOUS PLANTS 
arabin into a kind of glucose sugar, known as arabinose. A 
similar substance yielding arabinose forms about half of 
gum tragacanth, about one-third of the gum being a carbo- 
hydrate called tragacanthin (C,H,,O;) 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 
Fic. 156.—Gum Arabic Tree (Acacia Senegal, Pulse Family, Leguminose). 
A, flowering branch. B, flower. C, pod, half, showing seeds. JD, seed, 
cut between the seed-leaves to show seed-stem and seed-bud. JF, seed, 
cut across. (Taubert.)—A tree about 6 m. tall; bark gray; leaves 
grayish; flowers yellow; pod yellowish. Native home, tropical Africa. 
SS 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 C,,H,,0,, is obtained in large quantities from 
the outer coat of quince seed (Fig. 93). The slipperiness of 
