WHEAT (Triticum), the most important and the most generally diffused of cereal grasses, is an annual plant, with hollow, erect, knotted stems, and produces, in addi

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, and they only separate to allow of the passage of the empty anthers after fertilization. Within the pale are two minute, ovate, pointed, white membranous scales called "lodicles." 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 a rounded or oblong body, 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 last is a layer of square cells larger and more regular in form than those on each side ; these contain the gluten or nitrogenous matter upon which so much of the nutritive value of the seed depends. This thin layer of gluten cells contains the albumen or perisperm, which constitutes the great mass of the seed, being composed of numerous cells of irregular form and size filled with starch grains. These layers of cells become more or less dry and inseparable one from another, 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.

Such in brief is the general structure of the wheat plant as we now know it. Of its principal variations mention will be made below. What was its origin is not known ; and opinion has differed as to whether more than one species is involved or whether all the varieties now known may not have been originally derived from one. The prevalent opinion among botanists is that the wheat plant is nowhere found in a wild condition. Recently, however, M. Frederic Houssay is alleged to have discovered the plant wild in the mountains to the east of Kurdistan ; but the statement requires confirmation. Some of the species of the genus 2Eyi/ops (now referred to Triticum by Bentham and Hooker and by Haeckel) may possibly have been the sources of our cultivated forms, as they cross freely with wheats. Ilacekel, the latest monographer of the genus, considers that there are three species. (1) Trittcum monovated wheat, of which Haeckel recognizes three principal Egyptians, and throughout the Roman empire. The variety dicoccunt was also cultivated in prehistoric times, and is still grown in southern Europe as a summer wheat and one suitable for starch-making. Other sub-varieties 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 original home of the wheat plant was in Mesopotamia, and that from thence 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. sativunz - are very numerous and of every grade of intensity. Those 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 Prof. Church,' even in the produce of a single ear there may be 3 to 4 per cent. 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 100. From the point of view of agriculture (see vol. i. p. 354) 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. (1) 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. De Vilmorin points out that wheats of cold countries have flexible, thin, hollow straw, elongated fragile cars, and soft floury seeds ; Hunter's wheat may be cited as a good example. Wheats of hotter countries have a more solid, rigid straw, the ears short, stout, compact, the glumes provided with long awns or beards, and the seed hard and horny. Spring wheats procured from northern latitudes mature snore rapidly than those from temperate or hot climates, whilst the reverse is the ease 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 wheats, like the Egyptian, in plains or in ill-drained 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 straw-plaiting 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's 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 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 et-titivating. (4) Velvet-chaffed wheats do best in poor soil, and bearded wheats are usually hardiest. (5) 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.' The latest and fullest account is that of 11i. Henry de Yihnorin in his Les Ble's Areillcurs (Paris, 1881). The classification adopted by • this writer 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 soft wheats, turgid wheats (T. turgidam), hard wheats (T. durum), and Polish wheats (T. polonicum). In the soft wheats the chaff-scales are boat-shaped, ovoid, of the consistence of parchment, and shorter than the spikelet ; the seed is 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 soft wheats. In the hard wheats the outer ghillies are keeled, sharply pointed, awned, and the seed is elongated and of hard glassy texture, somewhat translucent, and diflicnit to break owing to its toughness. These seeds are richer in nitrogen than the soft wheats, so that an approximate notion of the richness in albnininoids may be gained by simply inspecting the cut surface of the seed. The Polish wheat, rarely if ever cultivated in the 'United Kingdom, has very large lanceolate ghunes, 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, fawn-coloured, 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 secti-n, and the entire or cleft palea. As illustrating the fact of the occasional instability of these variations, Prof. Church mentions that a single grain will be sometimes horny and partly opaque and soft, 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 suited to hot, others to cold countries ; some will flourish on one description of soil, others on another. Hence the 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 n the " infinite superiority " 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 Vilinorin, 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. 65° (Sehubeler), in Switzerland at an elevation of 1200 feet above the valley of Zermatt (or 6500 feet 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 'imposes the soft wheats, with their large relative proportion of starch, are the best, for others the hard wheats, with their larger quantity of gluten. With the modern processes of milling, the hard wheats are preferred, for they make the best flour ; and in North America the spring wheats are, as a rule, harder than the winter wheats. The sett wheats are those which are most general in European cultivation, and, as a rule, the beardless varieties, though more tender, are preferred. 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. Hard wheats are specially employed in Italy for the fabrication of macaroni. Polish when t 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 pastry-making ; but, owing to the construction of the grain, it requires special machinery for grinding (see FLotia).

The following passage, reproduced from a German source in Agrieullitrol Science (January 1887), may serve still further to illustrate the fitness of particular varieties for special purposes.

" Innumerable experiments have shown that the value of wheat for seed increases with the size of the grain: the larger kernel yields a stronger plant, and this will bear a heavier crop ; the smaller grain contains the larger proportion of gluten, yields a better flour, and brings a higher price ; but with the smaller yield per acre the profit may be less. The 'volume-weight' is dependent more on the well-rounded form of the grain than on its size ; when about alike in respect to shape, the market value of the grain is closely proportionate to its weight per bushel. Grain of a higher specific gravity Is usually richer in gluten. Richness in this constituent is of the greatest importance, as affecting the market value of the grain ; it gives better baking qualities to the flour, besides a higher nutritive value, and is aceoinpanied with greater riehness in phosphate, also an important constituent of animal food. The proportion of gluten in wheat is determined largely by the elimate, and especially by the proximity of the sea. Insular England produees a wheat grain with high absolute weight, but as a rule with less gluten than the wheat of eastern Europe. English wheat, and wheat in general grown In an ocean climate, seldom eontains over ten per cent: of gluten, while in eastern Europe and in the western United States the proportion rises to twenty per cent. and above. Vigorous English seed wheat sown in eastern Europe yields larger erops than the native seed, and a grain richer in gluten than the parent, though not so rich as wheat from native seed,,,z It is, however, to be observed that proximity to the sea does not produce soft wheat poor in gluten in Italy, Algeria, and other warm and tropical regions, where the plant is cultivated quite as much under the influence of the sea as in England. The soft wheat of Great Britain is to be explained rather by the mildness of the climate and the relative constancy of the temperature.

Wheat begins to grow at a temperature of 5° C. (41° Fahr.) ; and, when the aggregate temperature, as represented by the sum of the daily means, has mounted up to 185° Fahr., the germ begins to escape from the husk, if the seed be not 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 42° Fahr. When the young plants have been influenced by an aggregate temperature amounting to 1396° Rahn from the period when sown, or 1715° 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 55°, 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.

As for the soil requirements, see AGRICULTURE, vol. i. p. 357. 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 44i bushels of wheat to the acre, the soil must supply to the crop during its growth in round numbers-202 M of nitrogen, 81 11) of phosphoric acid, 55 Ib of lime, 26 Ib of magnesia, and 255 Ib of potash.

The numerous varieties of wheat now in cultivation have been obtained either by selection or by cross-breeding. In any wheat-field there may be observed on close inspection plants differiog in character from the majority. If seeds 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 has succeeded in introducing "pedigree wheats" of fine quality. But even greater results may be expected from cross-breeding, or the fertilization of the flowers of ono description of wheat by the pollen of another. This has been attempted by Shireff, Le Contour, Maund, and others in the past, and more recently by II. de Vilinorin and Messrs Carter. Under natural circumstances wheat is self-fertilized : that is to say, the pollen of any given flower impregnates the stigma and ovule of the same flower, the glunies 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 he seen protruding beyond the glines, and their position might lead to the inference that cross-fertilization was the rule ; but on closer examination it will Po found that the anthers are empty or nearly so, and that they are not protrude.d till after they have deposited the pollen upon the stigma. The separation of the plumes, which occurs at the time of fertilization, and which permits the egress of the useless stamens after that operation, is stated to occur only under certain conditions of temperature, when the heat, in fact, is sufficient to cause the Iodides of the flower to become turgid and thus to press apart the glumes. A temperature of about 75 Fahr. 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 inter-cross, and that even such a distinct form as the Polish is no exception. From this he concludes that all tire 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 Nandin "irregular variation." Sometimes characteristics appear in tire 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 soft wheat fertilized with the pollen of a hard variety, and spelt wheats among the descendants of a soft crossed with a turgid wheat. Other of De Vilmorin's experiments were made with the practical object of obtaining improved varieties or forms specially suitable to particular localities. Among those he has raised is one named "Dattel," which is highly esteemed ; it was got from the red Chiddam, a valuable variety, but one in which the straw is defective. By crossing tire red Chiddam with the pollen of Prince Albert a new variety has been produced which is stated to be early, very productive, and of good quality, as far as both grain and straw are concerned. Among many varieties raised by Messrs Carter some are very interesting : in one case the seed-parent was a short-strawed, downy-chaffed, awnless variety, the pollen-parent a large bearded American wheat. The offspring exceeded the seed-parent in stature by a foot, and had a smooth chaff and stout thickset cars with minute awns. Some of the crosses were made with the view to secure denser production of awns and thus to render the ears "bird-proof"; others were devised with a view of securing an early ripening variety, which was effected by crossing with the Talavera, a known early variety. The progeny was ready for cutting (in tire neighbourhood of London) on 21st July 1886.

To show how considerable may be the variations in the produce yielded by different varieties, the following figures, taken from the " memoranda sheet " of tire Rothamsted experiments, may be cited. For twelve successive years (1871-1882) Sir John Lawes cultivated 26 varieties of wheat, each variety each year in a different field and under different conditions of manuring. From various circumstances satisfactory averages were obtained during only eight years (1871-1878). The mean produce of all tire varieties taken together during that period was 431 bushels (dressed corn) per acre ; the lowest average produce was 36i bushels per acre, furnished by Hallett's original red ; and the highest produce was 53 bushels per acre, yielded by Rivett's red. As to manuring, the highest mean produce (51i bushels per acre) from 25 varieties taken together was obtained in 1878 on a field where all the 25 varieties were manured with 2 cwts. of nitrate of soda, the previous crop having been turnips, for which farmyard dung was applied, the turnips being partly consumed on the land, partly removed. Here again Rivett's red furnished the best crop (66! bushels per acre). This variety in almost - but not in all - cases gave the highest produce. The lowest mean produce from all the varieties taken together was 214 bushels per acre in 1879, - a most disastrous season. In that year even Rivett's red furnished no more than 16 bushels per acre, among the lowest on the record, but nearly twice as much as red Rostock, which in tire same year yielded only 8i bushels per acre, the manuring consisting of 2 cwts. of nitrate of soda after clover, partly cut, partly "fed." This same variety in another year and under a different condition of manuring yielded 57 bushels per acre. The disastrous effect of the season of 1879 was manifested not only in diminished produce hut in lessened germinative power ; in the season following white wheats appear to have been the worst, the most satisfactory crop in 1880 being yielded by Webb's "challenge," seeds of which were received direct from Stourbridge and not grown on the Rothamsted farm, as in the case of the other varieties. As to the weight per bushel of the grains of the different varieties at Rothamsted, there was a more limited range than in the case of the absolute weight, the highest mean (63i lb per bushel) being yielded by the "red nursery" variety, the lowest by Rivett's red (58i), the general average of all the varieties amounting to 611 tb per bushel. The effect of the bad season of 1879 was also shown here : the general average in that year was only 53i it per bushel, while in 1876 it was 63 for the same varieties. The greatest weight per bushel does not therefore correspond in all cases with the absolute amount of crop per acre, for a small crop often yields grain of relatively heavy weight. Nor does the same condition of manuring that brings an abundant crop necessarily yield a proportionate return calculated in weight per bushel. The greatest weight per bushel (63i lb in 1876) was secured on the same plot which in the same year yielded less than an average crop, 42A bushels per acre, very little difference being observable in the different varieties in point of quality, though much in quantity. The lowest average weight per bushel (56/ lb), however, corresponded with a very low total produce, 23k bushels per acre in 1880, on a poorly manured plot. These figures, added to those representing the cost for rent and taxes, manure, labour, and expenses of production generally, and considered in connexion with the enormous supplies imported from abroad, will show how great are the risks attendant upon wheat cultivation in the United Kingdom under existing circumstances ; but of course they are of little value as regards the growth of wheat in India and the colonies.

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 by land. The annual crop of the world is now estimated at nearly two thousand millions of bushels. Of late years tire increase of production has been most notable in southern Russia, Australia, India, and North America.1 Wheat is sometimes grown as a forage crop. A variety has been introduced from Japan by Messrs Sutton which seems to be very useful for this purpose. Although it takes a longer time to mature its seed, it flowers a fortnight earlier than other varieties. It seems also to be a hardy plant, having withstood successfully eight degrees of frost. From a crop sown on 27th August a sample was cut on the following 13th October, with a stem more than 2 feet in length and very thick and succulent, and the autumn was not very genial. This variety tillers well, so that it makes a complete mass of green stuff, which is very serviceable either for feeding sheep or for "soiling." (M. T. M.)