The odors exhaled by our own domestic plants have been but little studied, but the southern as well as many northern districts of the United States are well adapted for the cultivation of quite a number of species of plants which might be made to yield highly valuable articles of commerce. Among the plants which might furnish oils for the perfumer's use are, for instance, the wall flower, the Lilly, lilac and mignonette. VOLATILE OILS.--The volatile oils are either fluid (actual volatile oils) or solid (varieties of camphor) or solutions of solid combinations in fluid. The latter, on exposure to low temperatures, separate into two portions, one solid, called _stearoptene_, and the other liquid, called _elæoptene_. The boiling point of the volatile oils is considerably higher than that of water, but when heated with water they pass over with the vapors. Upon paper, fluid volatile oils produce grease spots, which differ, however, from those caused by fat oils in that they gradually disappear at an ordinary temperature, and rapidly by gentle heating. Most volatile oils are insoluble, or only with difficulty and sparingly soluble, in water, but they impart to the latter their odor and taste. They are readily soluble in alcohol, ether, chloroform, bisulphide of carbon and petroleum-ether, and miscible in every proportion with fats and fat oils. By their solubility in alcohol they differ from most fat oils. When freshly prepared many volatile oils are colorless, but soon turn yellow; some, however, show a distinct color even when fresh. They ignite with greater ease than fat oils and burn with a fierce smoky flame depositing a large amount of carbon. They exhibit a great tendency to absorb oxygen from the air and to gum, the influence of light promoting the process. In specific gravity they range from about 0.75 to 1.17, most of them being specifically lighter than water. Most bodies, under otherwise equal conditions, show always exactly the same specific gravity, the variations being so slight that they may be justly ascribed to errors of observation. However, one and the same volatile oil frequently shows such variations in specific gravity, that we are forced to ascribe this phenomenon to alterations in the constitution of the oil itself. For the exact determination of the specific gravity of a volatile oil, it should, therefore, be subjected to examination immediately after its preparation from the plant or vegetable substance, which should be as fresh as possible. The influence of light upon volatile oils is best shown by the following interesting experiment: If certain volatile oils are distilled in a vacuum or over burnt lime in a current of carbonic acid, it is no longer possible to distinguish, for instance, oil of lemon from oil of turpentine; however, by again exposing the oils to the air, they reacquire their characteristic odor.