EVERGREENS, in gardening, are those perennial plants which continue their verdure, leaves, &c. throughout the year, such as bays, hollies, pines, firs, cedars of Lebanon, &c.
In the evergreen shrubs and trees of this climate, such as heath, rue, box, laurel, &c. the leaf does not die in the autumn, but continues to supply nourishment to the bud in its bosom during the fine days of winter, and in the spring, and survives till near Midsummer, or till the new bud has expanded a leaf of its own. Hence Dr. Darwin supposes, that these evergreens lay up in summer no store of nutriment in their roots, or alburnum, for the sustenance of their ensuing vernal buds; and thus leave probably no bleeding season, like deciduous trees.
Mr. Milne, in his Botanical Dictionary, under the article Defoliatio, observes, that "an evergreen tree, grafted on a deciduous one, determines the latter to retain its leaves. This observation is confirmed by repeated experiments, particularly by grafting the laurel (Laurocerasus) an evergreen, on the common cherry (Cerasus); or the Hex, an ever-green oak, on the common oak."—All these, adds Dr. Darwin, want farther experiments, to authenticate the facts so delivered on the authority of ingenious men.
Evergreens are not only very great ornaments to a garden, at all seasons, but they also contribute to the purity of the air, when planted at a proper distance from dwelling-houses. Although their verdure, especially that of the pine and fir-trees, when scattered in rooms, exhales a narcotic and intoxicating effluvium, not unlike that of hops, yet the boughs of all evergreens may be usefully employed, particularly in winter, for correcting the stagnant air in a room: with this intention the branches are plunged with their root-ends into vessels filled with fresh water, and exposed to the rays of the sun; but not suffered to remain in the apartment during the night, or in the shade.