Page:An introduction to physiological and systematical botany (1st edition).djvu/101

Rh Resin is a substance soluble in spirits, and much more various in different plants than the preceding, as the Turpentine of the Fir and Juniper, the Red Gum of New South Wales, produced by one or more species of Eucalyptus, Bot. of N. Holl. t. 13, and the fragrant Yellow Gum of the same country, see White's Voyage, 235, which exudes spontaneously from the Xanthorrhœa Hastile. Most vegetable exudations partake of a nature between these two, being partly soluble in water, partly in spirits, and are therefore called Gum-resins. The milky juice of the Fig, Spurge, &c., which Dr. Darwin has shown, and which every body may see, to be quite distinct from the sap, is, like animal milk, an emulsion, or combination of a watery fluid with oil or resin. Accordingly, when suffered to evaporate in the air, such fluids become resins or gum-resins, as the Gum Euphorbium. In the Celandine, Chelidonium majus, Engl. Bot. t. 1581, and some plants allied to it, the emulsion is orange-coloured.

The more refined and volatile secretions of a resinous nature are called Essential Oils,