(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 seedling 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 outgrowth or "ligula." The inflorescence 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 out 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 together; 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, D E FIG. 1. - Spikelet and Flowers of Wheat.
A, Spikelet magnified.
B, Glumes, from side.
C, Glumes, from back.
D, Flowering glume or lower palea.
F, Lodicules 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 surmounted 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 longitudinal 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 endosperm, 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 composed of numerous cells of irregular form and size containing many starch grains as well as gluten granules. The several layers of cells above referred to become more FIG. 2. - I. Beardless wheat. II. or less dry and inseparPolish wheat, with seed. III. Spelt able one from another, wheat. 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 Triticum by Bentham and Hooker and by Haeckel) Origin and may possibly have been the sources of our cultivated Y P Y 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 1 found in those localities. (2) T. sativum 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 1 See drawings made to scale by Mr Worthington Smith in the Gardener's Chronicle (25th December 1886).
XXVIII. 19 other, the presumption is that they, like the species of Aegilops, which also intercross with wheat, may have all originated from one common stock.
Basing his conclusions upon philological data, such as the names of wheat in the oldest known languages, the writings of the most ancient historians, and the observations of botanical travellers, De Candolle infers that the hdistromeib u a n d original home of the wheat plant was in Mesopotamia, don. '' and that from there its cultivation extended in very early times to the Canaries on the west and to China on the east. In the western hemisphere wheat was not known till the 16th century. Humboldt mentions that it was accidentally introduced into Mexico with rice brought from Spain by a negro slave belonging to Cortes, and the same writer saw at Quito the earthen vase in which a Flemish monk had introduced from Ghent the first wheat grown in South America.
As might be anticipated from the cultivation of the plant from time immemorial and from its wide diffusion throughout the eastern hemisphere, the varieties of wheat - that is, of T. sativum - p r i nc i pa l are very numerous and of every grade of intensity. Those variations. cases in which the variation is most extreme some botanists would prefer to consider as forming distinct species; but others, as De Vilmorin, having regard to the general facts of the case and to the numerous intermediate gradations, look upon all the forms as derivatives from one. In illustration of this latter point it may be mentioned that not only do the several varieties run one into the other, but their chemical composition varies likewise according to climate and season. According to Professor Church,2 even in the produce of a single ear there may be 3 to 4% more of albuminoid matters in some grains than in others; but on the average the proportion of gluten to starch is as 9.11 to loo. From the point of view of agriculture it is generally of no great moment what rank be assigned to the various forms. It is only important to take cognizance of them for purposes of cultivation under varying circumstances. Hence we only allude to some of the principal variations and to those characteristics which are found to be unstable. (I) Setting aside differences of constitution, such as hardihood, size, and the like, there is relatively little variation in the form of the organs of vegetation. This indicates that less attention has been paid to the straw than to the grain, for it is certain that, were it desirable, a great range of variation might be induced in the foliage and straw. As it is, some varieties are hardier and taller than others, and the straw more solid, varying in colour and having less liability to be "laid"; but in the matter of "tillering," or the production of side-shoots from the base of the stem, there is much difference. Spring wheats procured from northern latitudes mature more rapidly than those from temperate or hot climates, whilst the reverse is the case with autumn wheats from the same source. The difference is accounted for by the greater amount of light which the plants obtain in northern regions, and, especially, by its comparatively uninterrupted continuance during the growing period, when there are more working hours for the plants in the day than in more southern climes. Autumn wheats, on the other hand, are subjected to an enforced rest for a period of several months, and even when grown in milder climates remain quiescent for a longer period, and start into growth later in spring - much later than varieties of southern origin. These latter, accustomed to the mild winters of those latitudes, begin to grow early in spring, and are in consequence liable to injury from spring frosts. Wheats of dry countries and of those exposed to severe winds have, says De Vilmorin, narrow leaves, pliant straw, bearded ears, and velvety chaff - characteristics which enable them to resist wind and drought. Wheats of moist climates, on the other hand, have broader leaves, to admit of more rapid transpiration. No doubt careful microscopic scrutiny of the minute anatomy of the leaves of plants grown under various conditions would reveal further adaptations of structure to external conditions of climate. At any rate, it is certain that, as a general rule, the hard wheats are almost exclusively cultivated in hot, dry countries, the spelt wheats in mountainous districts and on poor soil, turgid (durum forms) and common wheats in plains or in valleys - the best races of wheat being found on rich alluvial plains and in fertile valleys. The wheat used in the neighbourhood of Florence for strawplaiting is a variety with very slender stalks. The seed is sown very thickly at the beginning of winter and pulled, not cut, about the end of May, before the ear is ripe. In the United Kingdom ordinary wheat, such as old red Lammas and Chiddam white, is used for straw-plaiting, the straw being cut some time before the berry ripens. The propensity to "tiller" is of the greatest importance, as it multiplies the resources of the farmer. An instance of this is given in the Philosophical Transactions (1768), where it is stated that one seedling plant in the Cambridge botanic garden was divided into eighteen parts, each of which was replanted and subsequently again divided, till it produced sixty-seven plants in one season. In March and April of the following year these were again divided Food Grains of India, p. 94.
and produced 500 plants, which in due time yielded 21,109 ears.
(2) The variations in root-development have not been much attended to, although it would be well to study them in order to ascertain the degree of adaptability to various depths and conditions of soil.
(3) A most important difference is observable in the liability to attacks of rust (Puccinia), some varieties being almost invariably free from it, while others are in particular localities so subject to it as to be not worth cultivating. (4) The ears vary, not only in size, but also in form, this latter characteristic being dependent on the degree of closeness with which the spikelets are set on. In such varieties as Talavera the spikelets are loose, while in the club and square-headed varieties they are closely packed. The form of the ear depends on the relative width of the anterior and posterior surfaces as compared with that of the lateral surfaces. In the square-headed varieties the lateral surfaces are nearly as wide as the median ones, owing to the form and arrangement of the spikelets. The number of abortive or sterile spikelets at the top of the ear also varies: in some cases nearly all the spikelets are fertile, while in others several of the uppermost ones are barren.
The classification of the different varieties of cultivated wheat has occupied the attention of many botanists and agriculturists. Classit9ca The classification adopted by Henry de Vilmorin in his - Les Bles meilleurs (Paris, 1881) is based, in the first instance, on the nature of the ear: when mature its axis or stem remains unbroken, as in the true wheats, or it breaks into a number of joints, as in the spelt wheats. In the first class the ripe grain readily detaches itself from the chaff-scales, while in the spelts it is more or less adherent to them, or not readily separable from them. The true wheats are further subdivided into ?;? so ?!' l i: common wheats (T. vul- F,? 4,41 421 f gare), turgid wheats (T. Y ?` turgidum), hard wheats (T. ?yhJ durum) and Polish wheats (T. polonicum). In the common wheats the chaffscales are boat-shaped, ovoid, of the consistence of parchment, and shorter than the spikelet; the seed is usually floury, opaque, white, and easily broken. In the turgid wheats the glumes have long awns, and the seed is turgid and floury, as in the common wheats. In the hard wheats the outer glumes are keeled, sharply pointed, awned, and the seed is elongated and of hard glassy texture, somewhat translucent, and difficult to FIG. 3. - Longitudinal Section of a break owing to its tough Grain of Wheat; highly magnified. ness. These seeds are richer A, Epidermal cells. in nitrogen than the com B, Cells containing aleuron or gluten mon and turgid wheats, so grains. that an approximate notion C, Cells of endosperm or albumen, of the richness in albufilled with starch. minoids may be gained D, Embryo cut through the middle, by simply inspecting the root-end pointing downwards. cut surface of the seed. The Polish wheat, rarely if ever cultivated in the United Kingdom, has very large lanceolate glumes, longer than the spikelet, and elongated glassy seeds. Further subdivisions are made, according to the presence or absence of awns (bearded and beardless wheats), the colour of the ears (white, fawncoloured or red), the texture of the ears (glabrous - i.e. smooth - or downy) and the colour of the seed or "berry." In the jointed or spelt wheats the distinctions lie in the presence of awns, the direction of the points of the glumes (straight, bent outwards, or turned inwards), the form of the ear as revealed on a cross-section, and the entire or cleft palea. As illustrating the fact of the occasional instability of these variations, Professor Church mentions that a single grain will be sometimes horny and partly opaque and floury, in which case its composition will correspond with its aspect. The division into spring wheat and winter wheat is an agricultural one solely. Any variety may be a spring or a winter wheat according to the time at which it is sown. In the summer wheats it may often be observed that the median florets do not fill out so fully as in the autumn wheats. Among the turgid wheats there is a frequent tendency in the spike to branch or become compound - a tendency which is manifested to a less degree in other forms. The Egyptian, or so-called "mummy" wheat is of this character, the lower part of the spike branching out into several subdivisions. This multiplication of the seed-bearing branches might at first sight be considered advantageous; but in practice the quality of the grain is found to be inferior, as if the force that should have been devoted to the maturation of the grain were, in a measure, diverted and expended in the production of additional branches to the spike.
With regard to the chemical composition of the ripe grain, the Rothamsted experiments reveal a singular uniformity, even under very varied conditions of manuring, and even where much diversity was apparent in the constitution of the straw. A high or low percentage of nitrogen in the grain was also shown to depend more directly on the degree of ripening, as influenced by the character of the season, than on difference in manure; but it depends more upon the variety than upon soil or nutrition.
Apart from the botanical interest of these diversities, as indications of the faculty of variation in plants, and possibly as clues to the genealogy and origin of the cultivated plant, their practical importance is very great. Some varieties are bil;t to suited to hot, others to cold countries; some will flourish and on one description of soil, others on another. Hence the l ocality. paramount importance of ascertaining by experiment, not only what are the best varieties, but which are the best adapted for particular localities and particular climatic conditions. Porion and Deherain have shown 1 the "infinite superiority" in yield over the ordinary wheats of a particular square-headed variety grown on rich soil in the north of France. A good selection of seed, according to the nature of the soil, demands, says De Vilmorin, intelligence and accurate knowledge on the part of the farmer. If a good variety be grown in poor soil, the result will be unprofitable, while, if bad wheat be grown on good soil, the result may be nil. In botanical collections there exist, it is stated, herbarium specimens or other evidences of plants grown in Norway as far north as lat. 65Â° (Schubeler), in Switzerland at an elevation of 1200 ft. above the valley of Zermatt (or 6500 ft. above the sea), near the straits of Magellan, as well as in Teneriffe, the Cape of Good Hope, Abyssinia, Rodriguez, the Philippine Islands and the Malay Archipelago. These widely separated localities show the great area over which the culture is possible, and illustrate the powers of adaptation of the plant. The requirements of the consumer have also to be considered: for some purposes the soft floury wheats, with their large relative proportion of starch, are the best, for others the harder wheats, with their larger quantity of gluten. With the modern processes of milling, the harder wheats are preferred, for they make the best flour for bakers' use; and in North America the spring wheats are, as a rule, harder than the winter wheats. The bearded varieties are supposed to be hardier; at any rate they defy the ravages of predatory birds more completely than the unarmed varieties, and they are preferable in countries liable to storms of wind, as less likely to have their seeds detached. The durum (wheats are specially employed in Italy for the fabrication of macaroni. Polish wheat is used for similar purposes. Spelt wheats are grown in the colder mountainous districts of Europe; their flour is very fine, and is used especially for pastrymaking; but, owing to the construction of the grain,.it requires special machinery for grinding (see Flour).
Wheat begins to grow at a temperature of 5Â° C. (41 Â° F.); and, when the aggregate temperature, as represented by the sum of the daily means, has mounted up to 185Â° F., the germ begins to escape from the husk, if the seed be _tot deeply buried; but if it is deeply buried, an amount of heat is required greater in proportion to the depth. If the seed lies at a depth lower than a foot from the surface, it rarely germinates. The seedling plant ceases to grow if the mean temperature of the day remains below 42Â° F. When the young plants have been influenced by an aggregate temperature amounting to 1896Â° F. from the period when sown, or 1715Â° from the period of germination, branching or "tillering" goes on freely, and the young ears are formed. Under the influence of a mean temperature of 55Â°, or a little above, the flowers are produced. A still higher daily mean is required for the full development and ripening of the grain. The figures here cited are given by Risler and are calculated for the climate of Paris; but, of course, the same principles apply in the case of other countries. The amount of light and of moisture has also to be taken into account. The fact that the wheat plant requires less water than other cereals, and therefore does not suffer so much from drought, is one of great importance to the cultivator, and furnishes one reason for the greater proportionate culture of wheat in the eastern than in the western counties of England.
The following figures, cited by De Vilmorin from Joulie, will give an idea of the nature and amount of the demands made upon the soil by a wheat crop: in order to yield a crop of 442 bushels of wheat to the acre, the soil must supply to the crop during its growth in round numbers-202 lb of nitrogen, 81 lb of phosphoric acid, 55 lb of lime, 26 lb of magnesia, and 255 lb of potash.
The numerous varieties of wheat now in cultivation have been obtained either by selection or by cross-breeding. In any wheatfield there may be observed on close inspection plants produc- differing in character from the majority. If seeds of tio of these "sporting" plants be taken and grown in another season, they may (or may not) reproduce the particular variation. If they do, and the same process of selection be continued, the variation becomes in time "fixed," though it is always more or less liable to revert to its original condition. By continuously and systematically selecting the best grains from the best ears, Major Hallett succeeded in introducing "pedigree wheats" of fine quality. But even greater results may be expected from cross-breeding, or I Ann. agronom. (January 1888), p. 33.
the fertilization of the flowers of one description of wheat by the pollen of another. This has been attempted by Shireff, Le Couteur, Maund and others in the past, and more recently by H. de Vilmorin and Messrs Carter. Under natural circumstances wheat is selffertilized: that is to say, the pollen of any given flower impregnates the stigma and ovule of the same flower; the glumes and coverings of the flower being tightly pressed round the stamens and stigmas in such a way as to prevent the access of insects and to ensure the deposit of the pollen upon the stigmas of the same flower. This process of self-fertilization is the usual method, and no doubt keeps the variety true or unmixed; but the occasional presence of varieties in a wheat-field shows that cross-fertilization is sometimes secured. The stamens of the wheat plant may frequently be seen protruding beyond the glumes, and their position might lead to the inference that cross-fertilization was the rule; but on closer examination it will be found that the anthers are empty or nearly so, and that they are not protruded till after they have deposited the pollen upon the stigma. The separation of the glumes, which occurs at the time of fertilization, and which permits the egress of the useless stamens after that operation, occurs only under certain conditions of temperature, when the heat, in fact, is sufficient to cause the lodicules of the flower to become turgid and thus to press apart the glumes. A temperature of about 75Â° F. is found by Messrs Carter to be the most favourable. From what has been said it will be evident that the artificial fertilization of wheat is a very delicate operation. The glumes have to be separated and the anthers cut away before the pollen is fully formed, care being taken at the same time not to injure the stigma, and specially not to introduce, on the scissors or otherwise, any pollen except that of the variety desired. De Vilmorin's experiments have shown that all the varieties will intercross, and that even such a distinct form as the Polish is no exception. From this he concludes that all the forms have originated from one stock and are to be comprised within one species. In the progeny of these crossed wheats, especially in the second generation, much variation and difference of character is observable - a phenomenon commonly noticed in the descendants from crosses and hybrids, and styled by Naudin "irregular variation." Sometimes characteristics appear in the crossed wheats which are not found in the parent varieties, although they occur in other wheats. Thus, De Vilmorin records the presence of turgid wheats among seedlings raised from a common wheat fertilized with the pollen of a hard variety, and spelt wheats among the descendants of a common crossed with a turgid wheat.
The production of wheat, with the use of wheat bread, has increased enormously since the extension of railways has made possible the transportation of grain for great distances (see Grain Trade). Of late years the increase of production has been most notable in southern Russia, Argentina, Australia, India and North America.