CHAP. CIV.

«etui.a'cf.#:. be'tula.

1693

1550

Description. Thecommon birch, whenof a tree-like size, isknown, at first sight,by the silvery white-ness of its outer bark,the smallness of itsleaves in comparisonwith those of othertimber trees, and thelightness and airinessof its whole appear-ance. The tree, ascomparedwith others,is of the middle size,seldom exceeding 50feet in height, witha trunk of from 1 ft.to 18 in. in diameter,even in the most fa-vourable situations.

When drawn up inwoods, however, ingood soil, it has beenknown to attain theheight of from 60 ft.to 80 ft., but never,in such situations,with a trunk of pro-portionate diameter.

In the woods of Rus-sia, Pallas observes,

the birch is tall and erect, with a trunk not very thick; in the groves, thetrunk is thicker, and the head more spreading; and, in the open fields, thetrunk is short, the head broader than it is high, and the branches tor-tuous. The trunk is, in general, straight and cylindrical, without deformitiesand knots. The cuticle is white and scaly in trees from ten to thirteenyears of age; but in old trees the trunk is covered with deep black cleftsin its bark. The branches proceed chiefly from the summit, and are alter-nate, frequently subdivided, very pliant and flexible, and covered with areddish brown or russet-coloured smooth bark, which, as well as the buds,is slightly impregnated with a resinous substance. Both the trunk andbranches are occasionally subject to the production of excrescences; theformer as large knots, and the latter as twiggy tufts resembling large birds’nests. These twiggy tufts are seldom found on the weeping variety, andabound most on trees of the common sort growing on boggy soil. Theyare most probably formed by the extravasation of the sap, occasioned by thepuncture of some insect. The leaves are alternate, bright green, smooth,shining beneath, with the veins crossing like the meshes of a net; and thepetioles are J in. or more in length. The male catkins appear in autumn,on the ends of the twigs, but do not expand their flowers till the female cat-kins appear in spring. On young trees, and on old trees in particular situ-ations, especially in damp boggy soil, the branches are erect; but in old trees,and in some young ones more than in others, they are pendulous, and hencethe variety of that name. The roots extend themselves horizontally, anddivide into a great number of rootlets and hair-like fibres at their extremities;but they never throw up suckers. The rate of growth is considerable whenthe tree is young; averaging from 18in. to 2ft. a year for the first 10 years;and young trees cut down to the ground often make shoots 8 ft. or 10 ft. long