genus Pinus agree with the Scotch Pine in the construction of their flowers, and they differ from each other principally in their cones, and in the number of leaves which they have in a sheath. By far the greater number have two leaves in a sheath, (see _a_ in _fig._ 93,) and among these are the Scotch Pine (_P. sylvestris_), which has small straight cones without prickles; _P. Banksiana_, which has crooked cones; _P. pungens_ and other American Pines, which have prickly cones, every scale being furnished with a sharp spine; the Corsican Pine (_P. Laricio_), and several allied species, which have no spines on their cones, but every scale curving outwards; the Pinaster (_P. Pinaster_) which has large cones, with very short broad spines, and the Stone Pine (_P. Pinea_), the cones of which are smooth and shining, and very large, and the seeds of which are eaten. The pines that have three leaves in a sheath, are chiefly natives of North America, and have prickly cones; such as _Pinus Tæda_ and its allies, _P. ponderosa_, remarkable for its heavy wood which sinks in water, and its large spreading branches; and _P. Sabni_ and _P. macrocarpa_, which have long, slender, drooping leaves, and very large hooked cones. The pines which have five leaves in a sheath, include, among others, the Weymouth Pine (_P. Strobus_), the cones of which are long, narrow, and drooping (see _fig._ 95); _P. Lambertiana_, which has cones above a foot long; and _P. Cembra_, which has an oval cone, the scales of which are concave, and the seeds without wings. [Illustration: FIG. 95.—WEYMOUTH PINE (_P. strobus_).] THE GENUS ABIES.—THE SPRUCE FIR. [Illustration: FIG. 96.—SPRUCE FIR (_Abies excelsa_).] This genus includes all the Spruce Firs, and they are readily distinguished from the pines by their drooping cones (see _a_ in _fig._ 96), the scales of which are not thickened at the tip, but drawn out into a thin brittle membrane; and their leaves, which do not grow erect in sheaths, but in rows standing out from the branches (_b_), and which being the same on both sides, look as if two had grown together to make one. The difference between the Pines and the Firs will be seen clearly by comparing _fig._ 96, which represents a branch of the Spruce Fir, with _fig._ 97, which represents a branch of _Pinus pumilio_, a dwarf variety of the Scotch Pine. [Illustration: FIG. 97.—_Pinus pumilio._] [Illustration: FIG. 98.—THE SPRUCE FIR (_Abies excelsa_).]