146 THE USES OF PLANTS. 



like fracture and little or no smell or taste. The 

 term ' Gum-resin' is a correct designation for various 

 inspissated plant-saps which contain both gum and 

 resin. 



These definitions necessarily exclude that distinct 

 class of substances derived from the latex of plants, 

 and apparently present to some extent in all plants, 

 the caoutchoucs, or, more conveniently, ' Rubbers.' 

 These are insoluble in water, alcohol, or unconcen- 

 trated acid, and are essentially hydro-carbons, pro- 

 bably mixtures of two or more, together with an 

 oxidized substance. The introduction of Gutta 

 Percha in 1844, which will always redound to the 

 credit of the Society of Arts, and the discovery that 

 it, too, like Caoutchouc, might be made to unite 

 chemically with sulphur, thus becoming ' vulcanized ' 

 a discovery only made in the case of the other 

 substance a few years previously are among the 

 most revolutionary events in the history of commerce. 



It will be convenient to deal first with the true 

 Gums, then with the Resins, oleo-resins and gum- 

 resins, and, lastly, with the Caoutchoucs and Guttas. 

 The chief gum-yielding plants are the following : 



MIMOSE^E. 



Acacia. Various species, of which more will be 

 said, yielding the ARABIC, SENEGAL, and WATTLE- 

 GUMS, and part of the INDIAN TRAGACANTH or 

 KUTEERA. 



Prosopis dulcis, Kunth., and other species, such as 

 P. pubescens, Benth., of Mexico and Texas, and 



