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A tree attaining in America 100 to 125 feet in height, with a girth of 9 feet. Bark of old trees fissuring into small irregular plates. Buds, much larger than those of A. Lowiana, broadly conical, rounded at the apex, brownish, resinous, and slightly roughened by the raised tips of the scales. Young shoots smooth, yellowish-green, with a minute scattered pubescence, variable in quantity and often absent from the greater part of the branchlet. Second year's shoot greyish and irregularly fissuring.

Leaves on lateral branchlets irregularly arranged and not truly pectinate; most of the leaves extending laterally outwards and curving upwards, a few on the lower side directed downwards and forwards, some on the upper side directed upwards and forwards ; those above shorter than those below. Leaves up to 2 to 3 inches long, ¹⁄₁₂ inch broad, glaucous on both surfaces, linear, flattened, slightly tapering at the base, uniform in width elsewhere ; apex acute or rounded and not bifid, though occasionally a slight emargination is discernible with a lens; upper surface slightly convex, not grooved, with fifteen to sixteen regular lines of stomata; lower surface convex with two bands of stomata, each of about eight irregular lines, not con- spicuously white ; resin-canals marginal. Leaves on cone-bearing branches shorter, thicker, falcate, all curving upwards.

Cones, 3 to 5 inches long, 1¼ inch in diameter, cylindrical, narrowed at both ends, rounded or obtuse at the apex; greenish or purple before ripening, brown when mature. Scales of native Colorado specimens much broader than long ; lamina about 1 inch wide by 3 inch long, upper margin entire, lateral margins rounded and denticulate, gradually passing into the obcuneate claw or with a slightly auricled truncate base. Bract, at the base of the scale, rectangular, denticulate, with truncate upper margin and a minute mucro; in some specimens deeply bifid above. Seeds ⅓ inch long, with broad shining pinkish wings, about ½ inch long. In cultivated specimens, both brown and purple cones occur.

The following varieties have arisen in continental nurseries:—

1. Var. falcata, Beissner,’ leaves sickle-shaped, curving upwards.

2. Var. glabosa, Beissner,’ globose in habit, with symmetrical short branches,

1 According to the view taken here, Abies concolor includes only the tree found in Colorado, Utah, and Southern California. Sargent and other American botanists combine with this species the tree found in the Californian Sierras, which is considered by us to be a distinct species, A. Lowiana. The two forms differ remarkably in buds and foliage ; and it is most convenient to regard them as distinct species.

2 Mitt. Deut. Dendr. Ges. 1905, p. 112.