Online Encyclopedia

WHEAT (Triticum)

Online Encyclopedia
Originally appearing in Volume V28, Page 577 of the 1911 Encyclopedia Britannica.
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WHEAT (Triticum), the most important and the most generally diffused of cereal grasses. It is an annual plant, with hollow, erect, knotted stems, and pro- duces, in addition to the direct developments from the seed-ling plant, secondary roots and secondary shoots. (tillers) from the base. Its leaves have each a long sheath encircling the stem, and at the junction of the blade or " flag " with the sheath a small whitish out-growth or " ligula." The in-florescence or ear consists of a central stalk bent zigzag, forming a series of notches (see fig. 1), and bearing a number of flattened spikelets, one of which grows cut of each notch and has its inner or upper face pressed up against it. At the base of each spikelet are two empty boat-shaped glumes or "chaff-scales," one to the right, the other to the left, and then a series of flowers, 2 to 8 in number, closely crowded to- E. gether; the uppermost are abortive or sterile, indeed, in some varieties only one or two of the flowers are fertile. Each flower consists of an outer or lower glume, called the flowering glume, of the same shape as the empty glume and terminating in a long, or it may be in a short, awn or " beard." On the other side of the flower and at a slightly higher level is the " palea," of thinner texture than the other glumes, with infolded margins and with two ribs or veins. These several glumes are closely applied one to the other so as to conceal and protect the ovary, n ~ r A, Spikelet magnified. B, Glumes, from side. C, Glumes, from back. D, Flowering glume or lower palea. E, Palea. F, Lodicuies at base of j, the ovary, surmounted by styles. G and H, Seed from front and back respectively. I, Rachis, or central stalk of ear, spikelets removed. and they only separate for a short time when flowering takes place; after fertilization they close again. Within the pale are two minute, ovate, pointed, white membranous scales called " lodicules." These contain three stamens with thread-like filaments and oblong, two-lobed anthers. The stamens are placed round the base of the ovary, which is rounded or oblong, much smaller than the glumes, covered with down, and sur- mounted by two short styles, extending into feathery brush-like stigmas. The ripe fruit or grain, sometimes called the " berry," the matured state of the ovary and its contents, is oblong or ovoid, with a longitudinal furrow on one side. The ovary adheres firmly to the seed in the interior, so that on examining a longi- tudinal section of the grain by the microscope the outer layer is seen to consist of epidermal cells, of which the uppermost are prolonged into short hairs to cover the apex of the grain. Two or three layers of cells inside the epidermis constitute the tissue of the ovary, and overlie somewhat similar layers which form the coats of the seed. Within these is the albumen or endo- sperm, constituting the flowery part of the seed. The outermost layer of the endosperm consists of square cells larger and more regular in form than those on each side; these contain aleuron grains— small particles of gluten or nitrogenous matter. The remaining central mass of the seed is com- posed of numerous cells of irregular form and size containing many starch grains as well as gluten granules. The several layers of cells above re- ferred to become more Polish wheat, with seed. III. Spelt able one from another, -vheat. All much reduced. forming the substance known as " bran." At the lower end of the albumen, and placed obliquely, is the minute embryo-plant, which derives its nourishment in the first instance from the albumen; this is destined to form the future plant. The wheat plant is nowhere found in a wild condition. Some of the species of the genus Aegilops (now generally referred to Origin and Trilicum by Bentham and Hooker and by Haeckel) species. may possibly have been the sources of our cultivated forms, as they cross freely with wheats. Haeckel considers that there are three species. (1) Triticum monococcum, which undoubtedly grows wild in Greece and Mesopotamia, is cultivated in Spain and elsewhere, and was also cultivated by the aboriginal Swiss lake-dwellers, as well as at Hissarlik, as is shown by the grain' found in those localities. (2) T. salivum is the ordinary cultivated wheat, of which Haeckel recognizes three principal races, spelta, dicoccum and tenax. Spelt wheats (see fig. 2) were cultivated by the aboriginal Swiss, by the ancient Egyptians, and throughout the Roman empire. The variety dicoccum was also cultivated in prehistoric times, and is still grown in Southern Europe as a summer wheat and one suitable for starch-making. The variety tenax includes four sub-races, vulgare (common wheat), compactum, turgidum and durum (see below). (3) The third species, T. polonicum, or Polish wheat, is a very distinct-looking form, with long leafy glumes; its origin is not known. As these varieties intercross with each ' See drawings made to scale by Mr Worthington Smith in the Gardener's Chronicle (25th December 1886).
End of Article: WHEAT (Triticum)
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