ACACIA (literally, thorny, Gk. asic, akis, point, splinter, thorn). A genus of plants of the order Leguminos-e, differing from Mimosa in the greater number of stamens (10 to 200) and the absence of transverse partitions in the pods. There are about 450 species of Acacia, 300 of which are indigenous to Australia and Polynesia. The others are found in all tropical and sub tropical countries except Europe. The flowers are small and are arranged in globular or elon gated clusters. The leaves are usually bipin nately compound; but in many of the Australian species the leaflets are greatly reduced and the leaf blades correspondingly enlarged and flat tened into what are termed phyllodia. Most of the species having phyllodia inhabit hot, arid regions, and this modification prevents too rapid evaporation of moisture from the leaves. Many of the species are of great economic importance: some yield gums, others valuable timber, and still others food products. The African species, Acacia gummifera, Acacia seyal, Acacia chrenber giana, Acacia tortilis, and Acacia arabica, yield gum arable, as do the Asiatic species, Acacia arahica and the related Albizzia lebbek. A some what similar gum is produced by Acacia decur rens and Acacia dealbata of Australia and Acacia horrida of South Africa. Gum senegal is the product of Acacia verek, sometimes called Acacia senegal. The drug "catechu" is prepared from Acacia catechu. The astringent bark of a number of species is extensively used in tanning, especially the bark of those known in Australia as Wattles. For this purpose Acacia decurrens,
the Black Wattle, is one of the best, the air-dried bark of this plant containing about four times as much tanning extract as good oak bark. The most valuable timber tree of the genus is prob ably the Blackwood (Acacia melanoxylon), of Australia. The tree attains a large size, and the wood is easily worked and takes a high polish. A number of the Acacias have been introduced into cultivation in Europe and Amer ica, where they thrive. The California experi ment station recommends planting several species for tanning extract and for timber. A number of species are grown in mild climates and in greenhouses as ornamentals, partly because of the fragrance of their flowers. The foliage of some of the bipinnate species exhibits sleeping movements analogous to the movements of the sensitive plant. Sonic species show a remarkable sensitiveness to weather, the leaves remaining closed while the sky is cloudy. The common American Robinia or Locust (Robinia pseudacacia) and the Robinia hispida are known as Acacia and Rose Acacia in Europe and else where. Fossil forms of Acacia are abundant in the Tertiary beds of Aix in France, and an allied genus, rlcaeizephyllunl, has been described from the Cretaceous beds of North America. Consult: F. von Mueller, Iconography of Australian Acacias (Melbourne) ; L. H. Bailey, Cycloptrdia of American Horticulture (New York, 1900-01) ; G. Nicholson, Illustrated Dictionary of Garden ing (London, 1884-89).