food value are lessened. (353) For silage, it is generally de sirable to plant a variety which will develop a normal proportion of ears and that will get as mature as it is possible for maize to be when put in the silo. (349)

250. Comparative Yield of Dent and Flint Maize.-Almost all of the field maize of the United States, comparatively speaking, is of the dent type. Flint maize requires a smaller number of days to mature a crop; hence it is used in the more northern latitudes and at higher altitudes. It is the common field crop of New England. Each of these types has its place, but wherever the common varieties of dent maize will ripen flint maize usually is not desirable. For example, at the Pennsylvania Station eleven varieties of flint maize and fifteen varieties of dent maize have been tested from one to three years. The altitude is 1,200 feet; the season, therefore, is comparatively cool and short, and not especially adapted to the growth of dent varieties. The following table gives the yield of dry matter in pounds from ears and stover:

XI.

MAIZE.

IMPROVEMENT OF VARIETIES.

251. Pollination.-Maize is said to be wind-fertilized, since the extremely abundant pollen is carried long distances by the wind and often deposited upon silks of ears quite remote from the tassel bearing the pollen. Notwithstanding the large amount of observation and experiment, the extent to which maize is cross-fertilized and to what extent it is self-fertilized in actual practice has not been clearly established. It is believed by many, however, that since the pollen appears to develop slightly in advance of the silks of the same plant, and since the tendency of the currents of air would be to carry the pollen away from the plant producing it, that cross-fertilization is the rule and self-fertilization the exception. It has been clearly established, however, that both cross-fertilization and self-fertilization can readily be effected. Artificial or hand pollination usually does not produce as good results as when pollination takes place in the natural way.

The ovules are fertilized in order of sequence from butt to tip. Since the tip grains develop last, the tip of the ear is the most variable, due to variations in soil, cultural or seasonal conditions. It is probable that the filling out at the tip of the ear should be looked upon as the result of environment more than as an hereditary or variety characteristic. (243)

252. Influence of Current Cross.-The influence of pollen upon the grain or fruit which immediately develops, called xenia, has received considerable study especially in maize. That the character of the male pollen may affect the endosperm of the

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 genera tions; (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. cussing these results the Cornell Station says:

In dis

"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.