Bast, or PHLÆUM (formerly often called Liber, Inner Bark, or Endophlæum; see BARK), is a term applied by botanists to distinguish that portion of the fibro-vascular bundle which is characterised by the presence of sieve-tubes, from the woody portion which is distinguished by the presence of vessels (see BARK, VEGETABLE PHYSIOLOGY, DICOTYLEDON, &c.). These sieve-tubes (which are produced by the union of cell-rows, and are in communication by means of protoplasmic threads through oblique sieve-like partitions) are, like the wood-vessels, accompanied by a residue of undifferentiated cells, the bast parenchyma. These two elements constitute the soft bast, and through this layer the elaborated sap descends from the leaves throughout the plant. This region is recognisable under the microscope by the exceeding
Vessels (q.v.), but these are by no means essential to its structure. Juxtaposed to this soft bast we find the hard bast, which is entirely composed of cells, greatly elongated and thickened into the bast-fibres, and to this the important mechanical properties of bast (and consequently, for the most part, the strength, hardness, and toughness of bark) are essentially due. A bast-fibre has frequently a breaking strain greater than that of steel, and the varied economic applications of bast essentially depend upon the fineness and toughness of the fibre; thus the fibres of hemp, flax, jute, &c. are nothing else than bast. The name bast, however, is more usually applied to the inner bark of trees, and is common to the Teutonic languages, designating the inner bark of the Lime-tree (q.v.) or linden-tree, which is employed for making a coarse kind of ropes, mats well known as bast-mats, and a kind of shoes much worn by the Russian peasantry. The trees are cut when full of sap in spring. For bast to be plaited into shoes, young stems of about three years old are preferred; and it is said that two or three are required to make a single pair of shoes. Trees of six or eight years old are cut down for the better kind of mats, which are exported in large quantities from Russia, particularly from the port of Archangel, and which are much used for packing furniture, covering tender plants in gardens, supplying strands with which plants are tied, &c. The trees from which the bast is taken are very generally burned for charcoal. After the bark is dried, its layers are easily separated by steeping in water. The finest layers are the inner, and the coarser are the outer ones.—The manufacture of bast-mats is nearly confined to Russia and Sweden. Lime-tree bast is used in the south of Europe for making hats. The name bast-hat is, however, very often given to a hat made of willow-wood planed off in thin ribbons, and plaited in the same manner as straw-hats. The inner bark of Grewia didyma, a tree of the same natural order as the lime-tree, is used for making ropes in the Himalaya Mountains. See RAPHIA.