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varies widely with the variety, soil, climate and culture. In this country a good spike of wheat will usually contain from fifteen to twenty fertile spikelets and contain from thirty to fifty grains. There is a marked difference between the length of the spikes of English and American grown wheats. In the United States the length of the spike varies from three to four and a half inches, a common length being three and threefourths inches. Hallet has reported raising a spike of wheat eight and three-fourths inches long and containing 123 grains produced by five years of selection and favorable environment from a spike four and three-eighths inches long and containing forty-seven grains. Investigations by Lyon seem to show no relation between average weight of grain and the number on the spike.
The yield of wheat is affected by four factors, viz., (1) the number of spikes per a given area, (2) the number of spikelets in a given spike, (3) the number of grains in a spikelet, and (4) the weight of the grain. While there is no probability that such results as were reported by Hallet can be obtained in this country, it seems that the most hopeful method of increasing the yield is by increasing the number of spikelets in a spike.
The spike varies in compactness and in form. When viewed sidewise it may be straight or curved; may taper toward apex, both ways or have uniform sides, or may be clubbed at the upper end. The tip may be acute on account of undeveloped spikelets or blunt because they are well filled. The base of the spike may be tapering or abrupt for similar reasons. When viewed endwise the spike may be square, flattened with spikelets or flattened across spikelets.
60. The Grain.—The wheat grain is a unilocular, dry, indehiscent fruit called a caryopsis, with a thin membranous pericarp adnate to the seed, so that pod and seed are incorporated in one body. The grain is longer than broad, hairy at the apex, slightly compressed laterally, has a deep furrow on the side opposite the embryo, causing a deep infolding of the pericarp or bran, which makes the roller process of milling a superior method. It is characterized by a small embryo, and a large development of endosperm from which the flour is obtained. Bessey estimates the cubic contents of a wheat
grain to be from twenty to thirty cubic millimeters, of which fully thirteenfourteenths are filled with starch cells, the embryo occupying no more than onefourteenth of the space.1
61. The Embryo. —The embryo can be divided into (1) scutellum, or absorbent organ, which on germination causes the dissolution of the endosperm and then transfers it to (2) the vegetative portion. This vegetative portion contains in miniature the first leaves and roots of the new plant. The embryo contains a relatively high per cent of ash, protein and fat, and considerable quantities of soluble carbohydrates (sugar), but probably little if any starch. About one-sixth is fat or oil and about one-third is protein, the two thus constituting one-half of the embryo. The proteids of the embryo differ also from those of the endosperm in the ease with which they undergo changes. Osborne has found the embryo to contain about 3.5 per cent of nucleic acid.2
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Progressive sections of grain of wheat taken at the three axes as indicated, showing shape of grain and position and ratio of (jr) embryo to (y) endosperm. (From microphotographs by Rowlee.)
62. The Endosperm.—Under the microscope the endosperm is seen to consist of large elongated thin-walled cells, with their longer axis usually at right angles to the surface of the grain. These cells are filled with starch granules varying in size and form, but when full grown they are rounded or oval in shape and reach a diameter of thirty-seven micromillimeters, or 675 to t the inch.1 The composition of the flour shows the presence of ash and proteids, although under the microscope usually starch only can be seen in the mature grain. M. E. Fleurent has separated the endosperm from the rest of the grain and has subdivided it into three portions from the center outward.2 There was a material variation in the per cent of gluten in the endosperm of different varieties and a marked variation in successive portions from center outward, both in the per cent of gluten and the proportion of glutenin to gliadin. (70) Proceeding from center outward, the per cent of gluten varied in a French variety from 7.37 to 9.51, in an Indian variety from 8.03 to 10.24, and in a Russian variety from 10.88 to 13.22. The per cent of flour was largest (73-02 per cent) in the Indian variety and least (67.25 per cent) in the Russian variety.
63. The Aleurone Layer.—The endosperm, along with the embryo, is enclosed in a single row of comparatively large cells rather regular and rectangular in transverse or cross section. When viewed perpendicular to the surface these cells are irregular in form. The cells are filled with a substance similar in composition and physical properties to that found in the embryo, and are referred to as aleurone or gluten cells. The gluten of wheat flour does not come from the aleurone layer but from the endosperm.
64. The Bran.—The aleurone layer is enclosed in the nucellus, which in the mature wheat grain is a single layer of collapsed cells or may be wanting. This is enclosed in the
1 Neb. Bui. 32, p. 109.
* Compt. Rend. Acad. Sci., Paris, 126 (1898), No. 22, pp. 1592-1595.
unripe grain within two layers of cells, the inner and outer integuments of the ovulary. In the mature grain the inner integument may have been absorbed, leaving only the outer,
known as the testa. The testa is in turn enclosed by the pericarp, corresponding to the pod in the pea. The pericarp is composed of three rows of cells and constitutes a ratherlarger portion of the grain than do the testa and nucellus together. These envelopes are sometimes spoken of collectively as the bran. Bessey1 and Snyder * give different portions of the wheat grain as follows:
Aleurone layer 3-4
Seed covering or bran ..... 5
Girard gives the per cent of embryo in four varieties of wheat as 1.50, 1.41, 1.35 and 1.16 respectively.3
Since the mill products of wheat average considerably less than nine per cent crude fiber, and since seventy per cent of a wheat grain is converted into flour, it follows that the seed coats of the wheat grain must either be considerably less than
1 Neb. Bui. 32, p. in.
2 Harry Snyder: The Chemistry of Plant and Animal Life, p. 278. * Compt Rend. Acad. Sci., Paris, 124 (1897), p. 878.
Cross section of grain of wheat on the left. (From microphotograph by Tolman.) Transverse section, on the right, of an unripe grain enlarged about 100 times from drawing by Bessey. I, ovary wall or pericarp; 2, outer integument; 3, inner Integument; 4, remains of nucellus; 5, aleurone cells; 6, starch cells.
five per cent or the seed coats must be largely composed of something else than crude fiber.
65. Physical Properties.—Richardson found as the result of 377 determinations that there were about 12,000 grains in a pound of wheat: in some samples there were less than 8,000, while in others 24,000 grains to the pound. Obviously, so far as individual grains are concerned, one bushel of seed in the one case would be equivalent to three bushels in the other. Pammel and Stewart report variations in the specific gravity of American grown varieties from 1.146 to 1.518.
The hardness of the grain varies greatly. Generally the harder grains contain the higher per cent of total nitrogen and of gluten. The relation between hardness and specific gravity has not as yet been clearly demonstrated, although Lyon has shown that high specific gravity is associated with low nitrogen content.1
Kornicke and Werner2 state that the specific gravities of the various chemical constituents of the wheat grain are as follows: Starch, 1.53; sugar, 1.60; cellulose, 1.53; fats, 0.91-0.96; gluten, 1.30; ash, 2.50; water, 1.00; air, .001293.
The standard (and generally legal) weight per bushel (2150.42 cu. in.) of wheat is sixty pounds. The weight of a measured bushel not infrequently varies from fifty-five to sixty-five pounds per bushel, and greater extremes have been noted.
The color of the grain varies from a very light yellow through varying grades of amber to dark red. Hardness of grain and high nitrogen content are usually associated with the deeper red color.
The grain may vary in length, in transverse or cross section outline, or in depth of crease or furrow. All of these characters may be used in describing varieties of wheat. (201)
1 A Method for Improving the Quality of Wheat for Breadmaking. Thesis for degree Ph.D., Cornell, 1904.
'Handbuch des Getreidebaues Bd. 2s. 120. Berlin, 1884.