Var. minor, Tuckerman, is a dwarf form found upon the higher mountain summits of northern New England.
Habit.—A large tree, 50-75 feet high, with a diameter of 1-3 feet; occasionally of greater dimensions. The trunk develops a broad-spreading, open head, composed of a few large limbs ascending at an acute angle, with nearly horizontal secondary branches and a slender, flexible spray without any marked tendency to droop. Characterized by the dark metallic lustre of the branchlets, the dark green foliage, deep yellow in autumn, and the chalky whiteness of the trunk and large branches; a singularly picturesque tree, whether standing alone or grouped in forests.
Bark.—Easily detachable in broad sheets and separable into thin, delicately colored, paper-like layers, impenetrable by water, outlasting the wood it covers. Bark of trunk and large branches chalky-white when fully exposed to the sun, lustreless, smooth or ragged-frayed, in very old forest trees encrusted with huge lichens, and splitting into broad plates; young trunks and smaller branches smooth, reddish or grayish brown, with numerous roundish buff dots which enlarge from year to year into more and more conspicuous horizontal lines. The white of the bark readily rubs off upon clothing.
Winter Buds and Leaves.—Buds small, ovate, flattish, acute to rounded. Leaves simple, alternate, 3-5 inches long, two-thirds as wide, dark green and smooth above, beneath pale, hairy along the veins, sometimes in young trees thickly glandular-dotted on both sides; outline ovate, ovate-oblong, or ovate-orbicular, more or less doubly serrate; apex acute to acuminate; base somewhat heart-shaped, truncate or obtuse; leafstalk 1-2 inches long, grooved above, downy; stipules falling early.
Inflorescence.—April to May. Sterile catkins mostly in threes, 3-4 inches long: fertile catkins 1-1½ inches long, cylindrical, slender-peduncled, erect or spreading; bracts puberulent.
Fruit.—Fruiting catkins 1-2 inches long, cylindrical, short-stalked, spreading or drooping: nut obovate to oval, narrower than its wings; combined wings butterfly-shaped, nearly twice as wide as long.
Horticultural Value.—Hardy throughout New England; prefers a well-drained loam or gravelly soil, but does fairly well in almost any situation; young trees rapid growing and vigorous, but with the same tendency to grow irregularly that is shown by the black and yellow birches; transplanted without serious difficulty; not offered by many nurserymen, but may be obtained from northern collectors.
