fertilized ovule is certain. When sweet maize is crossed with dent pollen, the resulting grains have the appearance of flint grains, being neither dented nor wrinkled, and have the taste of dent maize. Sweet maize shows the influence of the current

Black Mexican sweet-white dent cross. Ear is Black Mexican sweet maize which was used as the male parent. Ear 2 is a white dent variety used as the female parent. Ear 3 shows the intermediate result of the cross, grains from which were planted to produce ears 4 and 5. Ear 4 was from the wrinkled or sweet grain of ear 3. Ear 5 was grown from the dent grains of ear 3 (after McCluer).

cross when pollinated by dent maize with such certainty that grains which do not show the effect may be depended upon to produce a pure product the next year. When sweet maize is

R. I. Rpt. 1901, pp. 227-244.

the male and dent maize the female parent, McCluer1 has shown both sweet and dent grain in the current cross, and that the dent grain when grown would show sweet characters. There is a strong tendency for color, where it is a character of the endosperm, to show in the current cross.

Webber has shown that the aleurone layer may be affected by the current cross. Cuzco, a soft variety, with heliotropepurple color in the aleurone layer, was crossed upon several varieties of dent maize, and grain resulting from such fertilization contained the same or similar color in the aleurone layer.2 The immediate effect of pollen upon the color when the color is in the seed coat, as in calico maize, is denied by some, and the observed instances have been explained by assuming that the seed of the female parent was impure.

253. Degree of Close Breeding.—There may be several degrees of closeness in breeding maize: (1) Between pollen and ovules of the same plant; (2) between pollen and ovules of plants grown from seed from the same ear; (3) between pollen and ovules of plants grown from seed from different plants of the same variety. The closeness of relationship of the plants furnishing the seed may vary between very wide limits. They may have had a common ancestor but one generation back, or they may have been unrelated in one or both ancestors for many generations; (4) between pollen and ovules of plants grown from seed of different varieties; (5) between pollen and ovules of plants grown from seed of different types.

254. Close Breeding.-Since cross-fertilization appears to be the rule in maize, it is generally considered desirable to avoid any practice which would induce close-fertilization. (106) Hopkins states that he has secured data pointing toward an injurious effect of close-pollination and recommends cross-pollination in

1 Ill. Bul. 21, p. 87.

2 Xenia, or the immediate effect of pollen in maize. U. S. Dept of Agr., Div. Veg. Phys. and Path. (1900) Bul. 22.

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." McCluer3 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.1

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 Ill. Bul. 82 (1902), pp. 535-536.

2 Science, N. S., Vol. XIII, No. 320 (1901), pp. 257-258.

8 Ill. Bul. 21, p. 96.

4 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

Summary of Results Obtained in Detasseling Maize.

In one trial the Illinois Station 2 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 Bul. 61 (1893), p. 312.

2 IL Bul. 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 per acre. 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)

1 Ill. Bul. 37, p. 20.

? Ill. Bul. 21, pp. 95-96.