BIRCH, (Betula), a genus of plants allied to the alder (Alnus), and like it a member of the family Betulaceae. The various species of birch are mostly trees of medium size, but several of them are merely shrubs. They are as a rule of a very hardy character, thriving best in northern latitudes—the trees having round, slender branches, and serrate, deciduous leaves, with barren and fertile catkins on the same tree, and winged fruits, the so-called seeds. The bark occurs in fine soft membranous layers, the outer cuticle of which peels off in thin, white, papery sheets.
The white or silver birch (B. alba) (see fig.) grows throughout the greater part of Europe, and also in Asia Minor, and Siberia, reaching in the north to the extreme limits of forest vegetation and stretching southward on the European continent as a forest tree to N. The male and female flowers are borne on separate catkins in April and May. It is a short-lived tree, generally from 40-50 ft. high with a trunk seldom more than r ft. in diameter. It flourishes in light soils and is one of the few trees that will grow amongst heather ; owing to the large number of "winged seeds" which are readily scattered by the wind, it spreads rapidly, spring ing up where the soil is dry and covering clearings or waste places.
This birch is one of the most widespread and generally useful of forest trees of Russia, occurring in vast forests, either in pure stands or mixed with pines, poplars and other forest trees. The wood is highly valued by carriage-builders, upholsterers and turn ers on account of its toughness and tenacity, and in Russia it is prized as firewood and a source of charcoal. Its pliant and flexible branches are made into brooms ; and in ancient Rome the fasces of the lictors, with which they cleared the way for the magistrates, were made up of birch rods. A similar use of birch rods has con tinued among pedagogues to times so recent that the birch is yet, literally or metaphorically, the instrument of school-room disci pline. The bark of the white birch is much more durable, and industrially of greater value, than the wood. It is impermeable to water, and is used in northern countries for roofing, for domestic utensils, for boxes and jars to contain both solid and liquid sub stances, and for a kind of bark shoes worn by the Russian peas antry. By dry distillation the bark yields an empyreumatic oil, called diogott in Russia, used in the preparation of Russia leather; to this oil the peculiar pleasant odour of the leather is due. The bark itself is used in tanning; and by the Samoiedes and Kamchatkans it is ground up and eaten on account of the starchy matter it contains. A sugary sap is drawn from the trunk in the spring before the opening of the leaf-buds, and is fermented into a kind of beer and vinegar.
Of some 10 species which belong peculiarly to North America, the most important economically are the yellow birch (B. lutea), the sweet, black or cherry birch (B. lenta), the red or river birch (B. nigra), and the paper or canoe birch (B. papyrifera). The yellow birch, one of the largest deciduous trees of north-eastern America, with a trunk 3 ft. to 4 ft. in diameter and occasionally 10o ft. high, grows from Newfoundland to extreme western On tario, and southward to central Iowa and North Carolina. It is cut for lumber chiefly in the Lake States and New York. The hard, close-grained wood, as heavy as that of red oak, is exten sively used for furniture and interior finishings. The sweet, black or cherry birch, which sometimes grows to a height of 8o ft. with a trunk diameter of 2 ft. to 5 ft., has smooth, red-brown, cherry like aromatic bark from which an oil very similar to the oil of wintergreen is extracted. It grows from Newfoundland to Iowa and southward to Florida, attaining its greatest size in the Appa lachian mountains, West Virginia and Pennsylvania, usually yield ing the largest cut of sweet birch lumber, often called cherry birch in the trade. The strong, hard yellowish-brown wood, as heavy as that of white oak, is highly valued for making furniture, agri cultural implements and woodenware. The semi-aquatic red or river birch, 8o ft. to 90 ft. high and sometimes 5 ft. in diameter, with dark red branches, grows from Massachusetts to Nebraska and south to Florida and Texas. It attains its greatest size in warm, wet lowlands along the Gulf coast, where it is the only birch. The strong light brown wood, which is cut for lumber in the South, is used for furniture and in turnery.
The paper or canoe birch, very similar to the European white birch, grows from Newfoundland and Labrador to Alaska as far as N., and southward to New York, Nebraska and Wash ington. It grows usually from 6o ft. to 7o ft. high with a trunk from 2 ft. to 3 ft. in diameter. Its creamy white, tough, durable bark, easily separable into layers, is used by the northern Indians for making canoes, drinking cups, dishes and baskets. The bark has also a limited use as a substitute for paper. The light, strong, close-grained wood is extensively utilized in turnery, especially for spools, shoe-lasts and shoe pegs, and also for wood pulp and fuel. From 190o to 192o the total birch lumber cut in the United States at times exceeded 400,000,00o bd. ft. annually, of which Wisconsin and Michigan usually contributed more than half ; in 1936 it was 184,000,00o board feet.