AL'DER (Alnus), a genus of plants of the natural order • bettaacem (regarded by many as a sub-order of amentamz. See Mum and AMENTACE,E, The genus consists entirely of trees and shrubs, natives of cold and temperate climates ,; the flowers in terminal, imbricated catkins, which appear before the leaves ; the male and female flowers in sepa rate catkins on the same plant ; the male or barren catkins loose, cylindrical, pendulous. having the scales 3-lobed, and each with three flowers whose perianth is single and 4-partite ; the fertile catkins oval, compact, having the scales sub-trifid, and each with two flowers destitute of perianth ; styles, two ; fruit, a compressed nut without wings.—The COMMON or BLACK A. (A. glutinosa) is a native of Britain, and of the northern parts of Asia and America. It has roundish, wedge-shaped obtuse leaves, lobed at the margin and serrated. The bark, except in very young trees, is nearly black. It succeeds best in moist soils, and helps to secure swampy river-banks against the effects of floods. It attains a height of 30 to 60 ft. Its leaves are somewhat glutinous. The wood is of an orange-yellow color, not very good for fuel, but affording one of the best kinds of charcoal for the -manufacture of gunpowder, upon which account it is often grown as coppice-wood. Great numbers of small A. trees are used in Scotland for making staves for herring-barrels. The wood is also employed by turners and joiners ; but it is particularly valuable on account of its property of remaining long time under water without decay, and is therefore used for the piles of bridges, for pumps, sluices, pipes, cogs of mill-wheels, and similar purposes. The bark is used for tanning and for dyeing, also for staining fishermen's nets. It produces a yellow or red color, or, with copperas, a black color. The leaves and female catkins are employed in the same way by the tanners and dyers of seine countries. The bark is bitter and astringent, and has been used for gargles, and also administered with success in ague. The seeds are a favorite
food of greenfinches.—The A. is one of the ornaments of many of the most exquisite landscapes in Britain. The dark -green of its foliage, and the still darker hue of its bark, contrast beautifully with the colors of the other trees with which it is usually associated on the banks of our rivers. In boggy grounds it is often almost the only kind of tree that appears, and in many parts of the highlands, groups of alders are scattered over the lower and moister parts of the mountain-slopes. The individual tree, viewed by itself,' may be regarded as somewhat stiff and formal in appearance; but in groups or clusters it is always far otherwise.—The common A. ceases on the Swedish shore of the gulf of Bothnia, in the s. of Angennannland, and is there called the Sea A., because it is only in the lowest grounds near the scat that it occurs.—The GRAY or WnimE A. (A. imam), a native of many parts of continental Europe, especially of the Alps, and also of North America, and of Kamtchatka, but not of Britain, differs from the common A. in having acute leaves, downy beneath, and not glutinous. It attains a rather greater height, but in very cold climates and unfavorable situations appears as a shrub. It occurs on the Alps at an elevation above that to which the common A. extends, and becomes abundant also where that species disappears in the northern part of the Scandinavian peninsula. The wood is white, fine-grained, and compact, but readily rots under water. The bark is used in cordifolia is a large and handsome tree, with cordate acuminate leaves, a native of the s. of Italy, but found to be quite hardy in England. Some of the American species are mere shrubs. The bark of A. serrulata is used in dyeing.— Several species are natives of the Himalayas.—The BEIMY-BEARING A., or A. Buck rrnoitN, is a totally different plant. See BUCKTHORN.