ACA'CIA, the name of n plant belonging to the order Leguminomr, mentioned by Dioscoridea, as a useful astringent thorn, yielding a white transparent gum. The account given by this Crack author, meagre as it accords so well with the gum-Arabic trees of modern Egypt, that we can scarcely doubt their identity. Accordingly it is to these, and to others closely related to them, that the classical name is still applied.
Amongst modern botanists the Acacia is a very extensive geniis of trees or shrubby plants, inhabiting the tropical parts of both the Old and New World, and, in a very few instances only, extending into temperate latitudes ; although over the whole of Australia, and its dependent islands, the species are spread in much abundance. There are nearly 300 species.
Generic Character.—Flowers polygamous. Calyx, with either four or five teeth. Petals, either four or five ; sometimes distinct front each other, sometimes adhering in a monopetalons corolla.. Stamens varying in number from 10 to 200. Pod not separating into many joints ; juicelesa, two valved. The species are extrema.). variable in the structure of their leaves and Some of them have true leaves that are twice or thrice pinnate, with a multitude of minute, shining, or at least even, leaflets; others have in a perfect state no leaves properly so called, but in their stead the leaf-stalks enlarge, and assume the appearance, and no doubt also the functions, of true leaves : species of the latter description are known by their spurious leaves being expanded vertically, instead of horizontally as in leaves of the ordinary construction. By these very remarkable points of difference in structure the species may be conveniently separated into two great subdivisions.
L Leaves pinnate(' in carious degrees. About 200 species known.
Acacia Gatechn (Wildenow), the Cateehu Acacia (Mimosa eateehm, !Anima). Spines growing in the place of the stipules; when young, straight, but afterwards becoming hooked. Leaves in ten divisions ; leaflets in from 40 to 50 couples, linear, downy; with one depressed gland at the base of the leaf-stalk, and from two to three between the upper divisions. Flowers arranged in cylindrical spikes, which grow
two or three together. It is n tree with n tolerably high and stout stem ; and is found in mountainous places in the East Indies, espe cially in Bengal and Coromandel. It is moat common in Carrara and Behar. Its unripe pods and wood yield, by decoction, one of the sorts of catcall', or terra-japonica. (Careenn.] A ea (-hi A rabiea (Roxburgh), the Gum-Arabic Treo. Spines growing in pairs. Branches and leaf-stelks downy. Loaves in from four to six divisions; leaflets in from ten to twenty couples, oblong-linear, with a gland between the lowest, and often between the outermost divisions. Heads of flowers growing in threes upon stalks. Pod necklace-shaped. It is an inhabitant of the Esat Indies, Arabia, and Abyssinia, where it forms a tree 13 or 14 feet high, of inelegant appearance ; easily recognised by its long curved pods, which are divided into a number of round compressed joints, by means of con tractions between the seeds. This is one of the plants that yield the ii-wful substance called Gum-Arabic, which is procured by wounding the bark ; after which the sap runs out, and hardens into transparent lumps, of various figures, very similar to the concretions found upon the bark of the cherry-tree in this country. Gum-Arabic is also pro duced abundantly by some of the species nearly related to this, such as A. Nilotica, or vera, found in Egypt ; A. L'hrenbcrgii, a native of Dongola ; A. tortilla, a common plant in the west of Nubia, Kordofan, and Arabia, especially upon Mount Sinai ; and A. Sepal, an inhabitant of Upper Egypt, Nubia, and western Arabia. It is supposed that (him-Arabic is collected, indifferently from all these, and that the gums of Jidda and Bassorah, Gum-Thur, and East India Gum, are only picked samples. Gum-Senegd is the produce of a distinct species, called A. Senegal, found in Arabia and the interior of Africa.