flax, common name for members of the Linaceae, a family of annual herbs, especially members of the genus Linum, and for the fiber obtained from such plants. The flax of commerce (several varieties of L. usitatissimum ) has been cultivated since prehistoric times (see linen). It was the major source of cloth fiber until the growth of the cotton industry (c.1800) and the competitive use of other fibers, such as jute. Flax has been transplanted from its native locales in Eurasia to all temperate zones of the world that provide a suitable habitat (a cool, damp climate) for its cultivation as a fiber plant; it is also grown in many tropical countries for its oil-bearing seeds. Flax plants grow to 4 ft (120 cm) in height and bear blue or white flowers that mature into bolls containing 10 seeds each. When grown for fiber, flax is sown densely to prevent branching and is gathered before maturity; for seed, it is sown sparsely and allowed to branch and fruit. To obtain the fiber, the stems, stripped of leaves, may be tied in bunches and immersed in warm water for a few days or in cool water for one or two weeks, or they may be spread out on grass and exposed to the dew and sun for several weeks. This process, called retting, permits bacteria to break down the woody tissues by fermentation and to dissolve by enzyme action the substances binding the fiber cells. After retting, the stems are washed and allowed to dry and then are scutched (beaten) to separate the fibers from other material and to crush the pith. A combing process (called hackling) removes any remaining nonfibrous matter. The fiber cells range in length from 1/2 to 2 in. (1.3–5.1 cm); the cell bundles (fibers) range from 12 to 36 in. (30–90 cm). Short, broken fibers are called tow and are used to make coarse fabrics and cordage; the long fibers are used for strong threads and fine linens. Flax fiber has also been used for such products as insulating material and writing and cigarette paper. The seeds are crushed to make linseed oil, and the remaining linseed cake is used for fodder; dried flaxseed has been used in various medicinal preparations. Flax is classified in the division Magnoliophyta, class Magnoliopsida, order Linales.