Gt'M TRAGACANTH, BRITISH GUM. WAX. 241 



in this country. In the spring, however, when the weather is 

 very dry, the gum can only be obtained by incisions made in 

 the bark. 



380. Gum Senegal is similar to Gum Arabic, being obtained 

 from a kind of Acacia differing very little from that which yields 

 the latter ; but it is of inferior quality. Gum Tragacanth, 

 which is obtained from a low prickly shrub growing in the 

 Levant, is in some respects different from the foregoing. It does 

 not dissolve freely in water ; but forms a thick mucilage with a 

 certain definite proportion of it. If this be mixed with a larger 

 quantity of water, it will separate again after a time and fall to 

 the bottom, leaving very little gum in the water above. This 

 gum is employed in some kinds of calico-printing, in which the 

 chemical action of the dyes on the other gums would injure their 

 qualities. The plant which yields this gum would flourish in 

 England ; but it can here only prepare no more of it than is 

 required for its own support ; and only possesses a superfluity 

 under the influence of a warmer climate. A large quantity of 

 a gum resembling that of the Acacia, may be obtained from the 

 various species of Lichen growing in this country, by the action 

 of hot water. The similarity of starch to gum has been already 

 noticed, and some of the sources from which it may be obtained 

 have been pointed out ; and it is here, therefore, only desirable 

 to add, that the gum obtained from starch is much used in the 

 arts, especially for the purpose of stiffening different fabrics, on 

 which account it is employed largely by calico-printers, under the 

 name of British Gum. 



381. The next Vegetable secretion to be noticed is Wax; 

 which, though commonly supposed to be formed by the Bee 

 alone, is undoubtedly present in many plants also. It may be 

 seen in the form of minute scales, upon the outer surface of the 

 Plum and other stone fruits, forming what is known as tire bloom ; 

 and it is by the existence of a thin coating of it, that the leaves 

 of the Cabbage, Tropaeolum (Sturtion), and other plants, are 

 enabled to resist moisture. "Wax may be obtained by heat, 

 though in small quantity, from the poplar, alder, and several 

 other plants ; but it exists in such abundance in the fruit of a 



