BE'TULA, a genus of trees or shrubs, belonging to the natural order Bet ulacem It is characterised by its flowers growing in catkins, the scales of which are thin and three-lobed, and by the scales subtending three fiat fruits, each furnished with two styles, and expanded into a thin wing on either side ; these fruits are what ara vulgularly called birch-seeds. The species are, with ono exception, found beyond the tropio in the northern hemisphere ; the species of the southern hemisphere is a little evergreen plant called B. antarctica, of which little is recorded except that it inhabits Tierra del Fuego.
The more remarkable species of this genus may be conveniently disposed according to their prevailing geographical distribution.
European Birches.
B. alba, the Common Birch. Branches erect, when young covered with a short close down never smooth, and warted ; leaves with a somewhat rhomboidal form, ovate, generally doubly serrated, with downy footstalks, acute, but not tapering to the point ; catkins pen dulous. A native of Europe from the most northern to the most southern countries, in the latter however not appearing except on mountains at a considerable elevation ; on /Etna it does not occur below 4762 feet above the sea, according to Philippi. It is also found eastward in Asia, as far at least as the Altai Mountains. Although this species is not much valued for its timber, it is extremely useful for many other purposes. Russia skins are said to be tanned with the empyreumatic oil of its bark, from which the peculiar odour of such leather is derived. Cordage is obtained from it by the Laplanders, who also prepare a red dye from it ; the young shoot serve to nourish their cattle, and vinegar is obtained from the fermented sap. The inhabitants of Finland use the leaves for tea, and both in Lapland and Greenland strips of the young and tender bark are used as food. From the timber are manufactured hoops, yokes for cattle, bowls, wooden spoons, and other articles in which lightness without much durability ie sufficient ; baskets and hurdles are often made of parts of its shoots ; and from its riling sap, extracted by means of openings cut into its alburnum in the spring, and fermented, a kind of wine is obtained which in of an agreeable quality, but will not keep. During the siege
of Hamburg by the Russians in 1814, almost all the birch-trees of the neighbourhood were destroyed by the Baalikirs and other barbarian soldiers in the Russian service, by being tapped for their juice.
The Birch naturally grows in poor sandy soil, on which it thrives folly as well as in that of a more fertile kind. It is said to attain sometimes the height of 70 feet, with a diameter of 2 feet ; in England it does not acquire such considerable dimensions As it approaches both its northern and southern limits it gradually decreases in size, conformably to the laws which regulate vegetable development. Its bark in said to be very durable.
B. pendia°, the Weeping Birch. Branches drooping, when young perfectly smooth, and marked with little pearly specks ; leaven with a somewhat rhomboidal form, ovate, either doubly or singly serrated, acute, but not tapering to the point, sometimes slightly hairy ; catkins pendulous Very common in different parte of Europe, along with the last, in the properties of which it appears to participate, and with which it ix often improperly confounded. It differs from the Common Birch not only in its weeping habit, but also in its young shoots being quite smooth, bright chestnut brown when ripe, and then covered with little white warts. The Bet eta politica of the nurseries is a slight variety, with a few straggling hairs on the leaves and leafstalks, and a lees drooping habit.
Common lltireh (Betule alba).
1, The inside of a barren scale, with the anthers attached ; 2, inside of a fertile scale, with the ovaries attached ; 3, an ovary cut through perpendicu larly ; 4, inside of a scale, with three ripe fruits; 3, a ripe fruit of the natural size ; 6, the same magnified; 7, a transverse section, and 8, a perpendicular section of the same; 9, a ripe seed ; 10, an embryo.