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seed maize breeding by detasseling alternate rows.1 Webber reports several instances of the injurious effect of inbreeding maize with pollen from the same plant, of which the following is an example: One hundred stalks of Hickory King grown from seed inbred with pollen from the same stalk yielded fortysix ears weighing nine and three-tenths pounds, while seed of the same race produced by crossing different seedlings yielded from the same number of stalks eighty-two ears weighing twentyseven and a half pounds. In another instance hybrids of the second generation, where seed was inbred, showed great loss of vigor, being small in structure and almost sterile.3 McCluer* found that plants grown from self-fertilized seed, besides producing smaller ears, produced a greater proportion of barren stalks and were subject to numerous deformities.
255. Detasseling.—Detasseling alternate rows of maize has been tried as a means of increasing the yield of grain, on the theory that plant food that goes to maturing the tassel and the production of pollen may be diverted to the grain. Ten stations have published results as shown in table on opposite page.4
In one instance the Cornell Station found an increase of fifty per cent in the detasseled rows, but ordinarily the increases and decreases found have fallen within twenty per cent. It should be noted that these percentages apply to only half the field. While the evidence is not entirely clear, the inference of experiments so far reported seems to be that increase from detasseling is most likely to occur on poor soil or in dry seasons. In discussing these results the Cornell Station says:
"The tassels were removed by hand by pulling them out as soon as they appeared. This operation was performed quite rapidly as comparatively little force was necessary to cause the stalk to break just above the upper joint and without
1 11i. Bui . 82 (1902), pp. 535-536.
2 Science, N. S., Vol. XIII, No. 320 (1901), pp. 257-258. S 11i. Bui. 21, p. 96.
* Ohio Rpt. 1897, p. 64.
any injury to the leaves whatever, if done before the tassels had become fully expanded. From the experiments in detasseling made at the station it is thought to be of prime importance to completely remove the tassel before it has expanded and commenced to shed pollen. As the tassel at this time is partially protected within the folds of the leaves, it can only be completely removed by grasping the top of the tassel and giving it an upward pull which causes it to break off as described above. Experiments in detasseling have been made at other experiment stations where the practice has been to remove the tassels by cutting them off with a corn knife which would either cause an injury to the leaves or a delay until the tassels had become fully expanded and had shed pollen, as some tassels will shed pollen while yet partially protected within the folds of the leaves. In either case a benefit ought not to be expected from the practice. Our experiments show that the object of removing the tassels is not accomplished if they are allowed to remain until fully expanded and become polleniferous."1
In one trial the Illinois Station2 found an increase of twentyseven per cent when tassels were pulled out and six per cent when cut out; — an increase of fifteen per cent when removed before tassels were expanded and eleven per cent when removed after tassels were expanded.
1 Cornell Bui. 61 (1893), p. 312. a 111 Bui. 37, p. 22.
256. Crossing.—What influence the crossing which the detasseling of alternate rows of maize compels has upon the subsequent progeny is not shown in the experiments just related, since to determine this it is necessary to grow the seeds thus crossed.
The Illinois Station 1 crossed a number of varieties in 1892, grew the cross-bred varieties in 1893 and again in 1894, comparing the yield with the average yield of the two parent varieties. In 1894, in four out of six cases, the yield was greatest for the cross, the average increase being twelve bushels peracre. In 1893 three out of four gave the largest yields for the cross, the average increase being two and threetenths bushels per acre; and in 1892 five crosses gave in every case a larger yield than an average of the parent varieties, the average increase being nine and a half bushels per acre. The conditions under which it was necessary to conduct these experiments made the results inconclusive.
When McCluer2 raised crosses from different types of maize, the progeny from the full cross was in nearly all cases increased in size as a result of the crossing. In nearly all cases this increase in size was not marked the second year, although yet larger than the average of the parent varieties. This may have been due to a tendency to revert to the character of the original ancestor or may have been due to each plat being grown from a single ear, thus bringing about at once inbreeding.
257. Disposition to Maintain Types and Varieties.—When sweet maize is crossed with a dent variety the grains of the current cross on the ear may all assume a smooth rounded appearance not unlike a flint variety. The plants that grow from these grains will produce ears which will have some grains of the dent type and some of the sweet type, thus showing a tendency to split up into the separate types and to prevent the production of an intermediate type. The same tendency is somewhat apparent, although less noticeable, in crosses between varieties of the same type. While the readiness with which maize cross-fertilizes tends to obliterate varieties, this tendency opposes it. (278)
258. Breeding for Composition.—Hopkins found that when analyses were made of different samples coming from a considerable number of ears that the composition of the grain was quite uniform. When, however, samples were taken separately, even from different ears of the same variety, there were considerable differences in the composition. Some variation was found in the composition of grains from the butt, middle and tip third of the ear, but when one or more rows were taken throughout the whole length of the ear the composition of this sample was found quite accurately to represent the whole ear. He further established the fact that if the grains of ears varying in composition were grown separately, this difference in composition would be found in the resulting crop. It was thus established that composition was hereditary. He also showed that the composition would be determined in considerable measure by the physical distribution of the parts of the grain.
259. Breeding for Fat.—As thirty-five per cent of the embryo is fat and as eighty to eighty-five per cent of all the fat of the grain is in the embryo, it is evident that grain with large embryos would contain larger percentages of fat than those containing small embryos, unless the per cent of fat in the embryo itself varied largely.1
Beginning with the same variety of maize, ears were selected four years for high fat and low fat content. Then rows were planted with both kinds of maize, every hill having each kind of maize just far enough apart to identify the stalks. Thus they were grown in the same season, in the same soil and under the same cultivation. The resulting crop from maize selected for low fat content contained three and eight-tenths per cent of fat; that for high fat, five and eight-tenths per cent of fat.2 In other instances ihere have been brought about
1 The investigations of Hopkins appear to show that large embryos contain a larger percentage of fat than small embryos. 11i. Bui. 87, p. 105.
2 11i. Bui. 87, p. 100.
variations in content of fat ranging from two and a half to seven per cent.
260. Breeding for Protein.—The relative proportion of glossy and white endosperm varies largely in the grains of different ears of the same variety of maize. In an average ear of Burr's white (dent variety) ten and two-tenths per cent of protein was found in the glossy endosperm and seven and eight-tenths per cent in the white endosperm. (226) Hopkins finds forty-two per cent of all the protein of the grain in the endosperm, and, also, holds that the aleurone layer, which also has a high per cent of protein, is larger in maize selected for high protein content . As the ratio of glossy to white endosperm is readily estimated by making selections of a few grains from each ear, assuming the above propositions established, maize may be bred for high or for low protein content . By this method, maize has been bred which contains but six and seven-tenths per cent of protein and as high as fourteen and four-tenths per cent .
Since the embryos contain a higher per cent of protein than the glossy endosperm and about the same percentage as the aleurone layer, it has been suggested that the variations in the per cent of protein were largely due to variations in the size of the embryos. Hopkins, however, has gone into a rather elaborate investigation to show that variations in the percentage of protein are due primarily to variations in the glossy endosperm and the aleurone layer and only secondarily to the variations in the embryo. 1
261. Breeding for Starch.—In order to breed for high starch content, we have only to breed for low protein and low oil content, as, practically speaking, the percentage of carbohydrates (principally
111i . Bui, 87, pp. 96-101.
The grains on the left contain the higher percentage of protein indicated by the higher proportion of glossy or corneous endosperm as compared with the white or soft endosperm, and, also, possibly, by the larger embryo. (After Hopkins.)