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maize becomes commercially successful. The absence of any one may limit successful production. If, for example, the area between the 700 and 8o° July isotherm be followed around the world in the northern latitude, it will be found that throughout the larger part of its course the rainfall is insufficient at those times of the year when it is most needed by the maize plant;

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Variation In amount and distribution of normal monthly rainfall, see map (276). For May, June, July and August, total normal rainfall is: Lincoln, Nebraska, I 5.7 inches; Tuscofa, Mlinois, I4.4inches; Columbus, Ohio, 13.2 inches; Western England, 10.7 inches'. Middle Germany, 8.6 Inches; Southeast Russia, 7 2 inches.l The great maize belt lies between the longitudes of Columbus, Ohio (83" 0' W. Long.), and Lincoln, Nebraska (96° 45' W. Long.).

or, where the rainfall is sufficient, physiographical feu.ures prevent the culture of maize on a large scale.

The so-called "corn belt" of the United States appears to have the best combination of temperature, sunshine, rainfall, soil and topography for the production of maize of any considerable area in the world.

1 Rainfalls for Lincoln, Tuscola and Columbus are from twenty-five-year averages of the United States Weather Bureau. The European figures are from Davis' Elementary Meteorology.

276. Influence of Temperature.—It is the temperature during the maize growing months of May to September inclusive, rather than the average annual temperature, that influences the production of maize. It is not only the temperature of air and soil as expressed by the thermometer, but also the sunshine, the influence of which is not fully expressed by thermometric readings. Brewer1 has shown that fifty-five per cent of the maize crop of 1879 in the United States was grown between July

isotherms 750 and 80° F. and thirtythree per cent between 7o°and 750 F., making a total of eighty-eight per cent between July

Map showing area in Northern Hemisphere between July Iso. isotherms 70° F. therms, 70° and 80° F., Indicating suitable temperature for , Q O -p the production of maize. Note rainfall in chart (275). •

It is difficult to

give precise limits to an influence which is one of several absolutely necessary. Beale3 has compared the yield of maize with the temperature in each of the nine leading maize producing States, viz., Ohio, Indiana, Kentucky, Tennessee, Illinois, Iowa, Missouri, Nebraska and Kansas, during the five months May to September inclusive for sixteen years. No relation in these favored States could be traced between yield per acre and temperature.

Temperature is well known to influence maturity and may thus, indirectly at least, affect yield of merchantable grain, especially in regions near the northern limit of successful culture. The New York State Station3 compares the soil temperature with yield in crops of different maturity, as follows:

l Tenth Census U. S., Vol. Agr.

* H. G. Beale: Thesis, B. S. Degree, Ohio State University, 1902. * N. Y. Rpt. (Geneva) 1886, p. 39.

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277. Influence of Climate Upon Habit of Growth.—There is greater variation in the habit of growth of the maize plant than in any other cereal. These variations within any one of the five types of maize seem to be correlated with the climatic conditions as indicated by the great variation in size and in the time of maturity in northern as compared with southern latitudes.

The growing season for maize varies in different sections of the United States from ninety to 160 days and varieties exist which are adapted to these different growing periods. In general it may be said that as we go north or south of a given latitude a variety becomes one day later or earlier for each ten miles of travel, the altitude remaining the same. That is to say, a variety which ripens two weeks before a killing frost in a given locality would only barely ripen if taken 140 miles farther north, the altitude remaining the same. Care should be taken, therefore, in selecting new varieties, to get them from the same latitude. If obtained from much farther north they may ripen too early and consequently be too small. If obtained much farther south, they may not ripen.

Size and period of growth are also influenced by moisture. Under conditions of favorable water supply, the plant continues to grow, while a deficiency will reduce growth and hasten ripening.

278. Influence of Climate Upon Varieties.—Whether the environment was a cause of variation or whether selection, it is probable

r that there is a relation between climate and existing varieties of maize. The time that it has taken to fix these types is, however, a matter of much difference of opinion and about which the evidence is obscure. The variations as to size and maturity existed when this country was discovered. It is a common observation that the varieties of a given region tend to assume a common type. When dent varieties are introduced in a region growing flint varieties, or the reverse, the introduced variety tends to take on the characters of the other type. This has been attributed to climatic influences, but may be explained upon the grounds of crossing and unconscious selection. The current cross would not, ordinarily, show in the seed, but would show in the resulting crop. Varieties sufficiently distinct to escape cross-pollination have been grown continuously without modification.1

The author had a standard variety of maize grown about 120 miles north of the Illinois Station for three years. The first season it barely ripened in its new location. The ripest ears were selected for seed, and in subsequent years it was believed by the grower to have ripened earlier. After three years seed was returned to the Illinois Station and on the fourth year grown beside seed continuously grown at the station. When thus grown side by side there was no difference in the time of ripening. The evidence concerning the influence of climate upon varieties is not as clear as might be desired, but it is probable that much that has been ascribed to climate has been due to selection.

279. Influence of Climate Upon Composition.—Analyses so far reported do not indicate any material difference in composition in maize grown in different sections of the country covering a wide variation in soil and climate. An average of thirty-five northern and forty-nine southern grown samples of dent maize has shown the following composition:

1 Cf. Bui. Torr. Bot. Club Vol. XXI (1894), No. 12, p. 521.

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280. Need of Water.—At the Illinois Station, from eighteen varieties of maize on eighteen tenth-acre plats, the author obtained thirty-two bushels of dry shelled grain per acre. The next season, with the same varieties on the same plats, with cultural methods as nearly identical as possible, and without the addition of any fertilizer, ninety-four bushels per acre were obtained. During the first season, the rainfall for the five growing months (May to September) was thirteen inches; during the second, twenty-two and a half inches. During the same period the average temperature for the first season was 730 F.; the second, 690 F. (276)

The amount of water evaporated from the maize plant and the surrounding soil has been determined by King1 to be in Wisconsin 270 pounds for each pound of dry matter grown, equivalent to a rainfall of 2.4 inches for each ton. This is only about half that required by oats and clover. Maize is, however, very greatly influenced by the water supply in July and August, since during that time the period of growth is very rapid. The author has determined the growth of maize in one week in July in Illinois to be equal to 1,300 pounds of dry matter per acre, which would require, according to the experiments of King, 1.5 inches of rainfall. (350) At such times, unless the physical conditions of the soil are the best, the plant is apt to suffer from a lack of water, or, in other words, from drouth.

281. Influence of Rainfall.—Everything points to the importance of water in the successful culture of maize. Beale has

1 King: Physics of Agriculture, p. 139.

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