Linnæus placed nearly all the hardy Abietineæ in the genus Pinus, and since his time botanists have disagreed exceedingly respecting the generic names of the different plants; no less than twelve different divisions of them having been published, by as many eminent botanists, since the commencement of the present century. The best, however, appears to be that of M. Richard, which was approved by De Candolle, and which has been adopted with a slight alteration in Mr. Loudon’s _Arboretum Britannicum._ According to this arrangement, the hardy Abietineæ are divided into five genera; viz., Pinus, the Pine, including all the resinous trees with long leaves, which grow two or more together in a sheath; Abies, the Spruce Fir, the leaves of which do not grow in a sheath, but are scattered round the branches, the leaves themselves being short, flat, and the same on both sides; Picea, the Silver Fir, the leaves of which resemble those of Abies, except that the edges curl in, and the under surface is quite different from the upper one, being marked with two white lines, one on each side the midrib; the leaves are also placed nearly in two rows, one on each side the branch; Larix, the Larch, the leaves of which are very slender and produced in tufts, but which fall off every winter; and Cedrus, the Cedar, the leaves of which resemble those of the Larch, but which do not fall off every winter. The distinctions between these genera in the leaves only are very clear, and easily remembered; and their cones differ as decidedly: those of the Pines are hard and thick at the tips of the scales, which remain on after the seed drops; those of the Spruce Firs are thin at the tips of the scales, which also remain on the cones after they have lost their seeds, and the cones are drooping, and tapering at both ends; those of the Silver Firs are erect, cylindrical, and of nearly the same diameter throughout, and the scales fall with the seeds; those of the Larch are erect, but small and conical, and the scales remain on after the seeds have fallen; and those of the Cedar are erect, oval, and with deciduous scales. To the hardy genera may now be added Araucaria, as one species of this genus (_A. imbricata_) has been found quite hardy in Britain. The Cupressineæ are divided into four or five genera; viz., _Thuja_, the Arbor Vitæ, some of the species of which have been formed into a new genus under the name of Callitris; _Cupressus_, the Cypress; _Taxodium_, or _Schubertia_, the deciduous Cypress; and _Juniperus_, the Juniper. The only needle-leaved trees belonging to Taxineæ belong to the genus Taxus, the Yew, unless we separate from it the new genus Torryea. § 1. THE ABIETINEÆ.—THE PINE AND FIR TRIBE.