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I. STRUCTURE (CONCLUDED).
225. The Embryo.—The scutellum and vegetative portion with its miniature leaves and roots can readily be seen with a low power microscope. (61) The embryo situated on the side toward the tip of the ear, while variable in size, is relatively large, variations of from 7.7 to 15.7 per cent having been reported.1 In an average ear, not far from one-eighth of the grain is embryo. (60) The embryo is characterized by high percentage of ash, protein and fat. The following per cents in the water-free substance of the embryo have been reported:2
In dent maize the embryo contains about twenty per cent of the protein, seventy-five per cent of the ash and eighty to eightyfour per cent of fat of the whole grain.3
226. The Endosperm,—A section of the endospermferies from snowy white to translucent in appearance. The difference between the types or subspecies of maize is in part based upon the relative amounts and arrangements of the white and translucent or corneous endosperm. When cross-sections of the
1 11i. Bui. 55, pp. 234-235.
* 11i. Bui. 53, p. 140; 87, p. 83.
I 111. BuL 87, pp. 90-91.
A, an enlarged longitudinal section of maize. The internal structure is diagrammatic inasmuch as about 100 times the number of cells in outline (ten times in diameter) occur in the grain. I and 2 show the pericarp; the testa is not shown in A, but is shown in B 1 0. The nucellus is wanting. 3, aleurone layer; 4, cells of the endosperm; 5, scutellum; 6, plumule; 7, primary root; 8, its root-sheath; 9, a row of cells similar in appearance to aleurone layer but smaller. B, section more highly magnified; shows pericarp composed of two layers; I , epicarp; 2, endocarp. (The author.)
maize grain are examined under the microscope, no material difference in structure is noticeable. This has led to the suggestion, not positively proven, that the difference between the white and translucent portions of the endosperm is a difference in density analogous to the difference between snow and ice. The difference is readily noted in pop maize before and after popping.
Hopkins reports finding corneous endosperm to contain two per cent more protein than the white endosperm in a dent variety, and makes this the basis of selecting strains of maize for high protein.1 The question may be raised whether the higher percentage of protein found in the corneous endosperm may not be due to lack of complete separation from the aleurone layer. On the other hand, a somewhat similar condition exists in the endosperm of wheat. (62) Analyses of dent, flint, pop and soft varieties of maize in which there are wide differences in the density of the endosperm do not show material differences in the per cent of protein in the whole grain.
The endosperm occupies about seventy-three per cent of the grain, contains about sixty per cent of the protein, four per cent of the fat, twelve per cent of the ash and about eighty per cent of the carbohydrates, principally starch, of the whole grain.
The endosperm contains six to ten per cent of protein, eightynine to ninety-three per cent of carbohydrates and usually less than half a per cent each of ash and fat. It appears probable that the fat found in the endosperm on analysis may be there through absorption from embryo and aleurone layer, since the per cent of fat in endosperm is found to increase with the age of the grain.2 In sweet maize the starch has been changed in part to sugar.
227. The Aleurone Layer is relatively larger than in the wheat grain, comprising from eight to fourteen per cent of the
1 111. Bui 87, pp. 83-84. * I1L BuL 87.
maize grain; otherwise it does not differ materially in structure from that of wheat. (63) It contains a slightly greater percentage of protein, considerably greater percentage of carbohydrates and a much less percentage of ash and fat than the embryo.
228. The Hull -In dent maize the hull, including the cap at the base of the grain, constitutes, according to Hopkins,1 about seven per cent of the grain.
The hull is easily removed from the aleurone layer after soaking in hot water for fifteen minutes. The pod or pericarp, the integuments or testa, and the nucellus or perisperm, which constitute the hull, are not easily separable and cannot be distinguished except upon microscopic examination. (67) In the ripened grain the pericarp forms the larger part of the hull, the testa being compressed and the nucellus much reduced.2 While under the microscope, the hull appears to be composed chiefly of cell walls or cellulose, Voorhees* reports the following composition of the dry substance: Ash, 1.3; protein, 6.5; fiber, 16.2; nitrogen-free extract, 74.4; fat, 1.6. The nitrogen-free extract of the hull appears to be largely gum (pentosan) rather than starch.
229. Color.—A very large variety of colors is known to occur in the grain of different types of maize. The most common colors of all types except sweet maize are yellow or white or some shade between. In this case the color is due to that of the endosperm and possibly also the aleurone layer, but is not
J 11i. Bui. 87, p. 83.
2 Iowa Bui. 54 (1901), p. 132.
'11i. Bui. 53, p. 140.
Cross section of the outer portion of a grain of maize; p, pericarp; t, testa or integuments; n, nucellus; a, aleurone layer; s, endosperm (adapted from Webber).
due to the hull, which is translucent and merely transmits the color from the enclosed material. In blue, purple and black of the soft and sweet types the color has been shown to be in the aleurone layer.1 In the case of the red color often occurring in dent varieties the color is in the hull, as can readily be seen upon its removal. This colored hull may overlie a yellow or a white endosperm. The continued appearance of red ears in yellow or white varieties of dent maize, although such ears are seldom used for seed, is an interesting phenomenon not yet satisfactorily explained, although sometimes claimed to be due to atavism. By selection the red color may become fixed.
There is no evidence that color affects composition or feeding quality. White varieties are more common in the southern portion and the yellow varieties are more common in the northern portion of the United States. The Mississippi Station in 1895 compiled the yields of white and yellow varieties at seven stations in the central and southern Mississippi Valley. In 1,267 tests with 490 varieties, the average yield of 217 white varieties was found to be 2.5 bushels per acre in excess of the yield of 273 yellow varieties. At only one of the stations (Indiana) have the yellow varieties given the better yield.
"In connection with the tabulation of the records of corn yields at different stations a careful examination was made of the reported yields of wheat and oats, and, without going into details, it may be stated that in both the white varieties have given the heavier yields." 2 (386)
This difference in the case of maize is probably due to the more southern origin and later maturity of the white varieties as compared with the yellow varieties rather than to any inherent influence due to color.
230. Abnormal Growths.—The maize plant is subject to numerous abnormal changes. Among these may be mentioned tassel grains, one or more ears at nodes of branch in addition
1 Webber, H. J.: U. S. Dept. of Agr., Div. of Veg. Phys. and Path. Bui. 22. 1 Miss. Bui . 33 (1895), p. 69.