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 spike lets are set on. In such
varieties as Talavera the spike lets 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.
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| Fig. 3.—Longitudinal Section of a Grain of Wheat, highly magnified. | ||||||||
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The classification of the different varieties of cultivated wheat has occupied the attention of many botanists and agriculturists. Classification of cultivated wheats. The classification adopted by Henry de Vilmorin in his Les Blés 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 common wheats (T. vulgare), turgid wheats (T. turgidum), hard wheats (T. durum) and Polish wheats (T. polonicum). In the common wheats the chaff-scales 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 break owing to its toughness. These seeds are richer in nitrogen than the common and turgid wheats, so that an approximate notion of the richness in albuminoids 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 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, 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-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 Adaptability to soil and locality. 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 Dehérain 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. 65° (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 specialty 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 pastry-making; but, owing to the construction of the grain, it requires special machinery for grinding (see Flour).
Wheat begins to grow at a temperature of 5° C. (41° F.); and, when the aggregate temperature, as represented by the sum of the daily means, has mounted up to 185° F., 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° F. When the young plants have been influenced by an aggregate temperature amounting to 1896° F. from the period when sown, or 1715° from the period of germination, branching or “tellering” 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.
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 44½ bushels of wheat to the acre, the soil must supply to the crop during its growth in round numbers—202 ℔ of nitrogen, 81 ℔ of phosphoric acid, 55 ℔ of lime, 26 ℔ of magnesia, and 255 ℔ of potash.
The numerous varieties of wheat now in cultivation have been obtained either by selection or by cross-breeding. In any wheat-field Production of varieties. there may be observed on close inspection plants differing 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 succeeded in introducing “pedigree wheats” of fine quality. But even greater results may be expected from cross-breeding, or
- ↑ Ann. agronom. (January 1888), p. 33.
