Since wheat hybrids naturally self-pollinate, it would be ex pected that they would follow the same law, and Spil...an found

lated characteristics combined in making up the unit of higher value per acre will continue their united excellence has been questioned. Hays' experience indicates that at least a part of the hybrids which show most vigor in value per acre during the first several years after the hybrids are formed will continue to yield well of good grain. Mendel's results add assurance to the hope that at least part of the complex compound of characters formed in producing a lot of wheat hybrids will remain stable. Hybrids made by Saunders, Hays and others and widely distributed retain their characteristics apparently unchanged.

108. Method of Finding and Testing New Strains or Varieties. -The methods of improving wheat by experiment and seed stations now recognize the individual wheat plant as the unit from which selections are made. From whatever source the seed is

obtained, whether from crossing, by selection from a field or simply from the bin, seeds are planted individually in rows any suitable distance apart,-usually four by four inches for spring wheat and five by five for winter wheat. The larger the number of individual plants the better.

If any plants are found among those thus grown that possess characteristics desirable to perpetuate, one hundred seeds, more or less, are planted as above indicated in order to determine the ability of the selected plant to transmit its characteristics or in the case of cross-bred varieties by continued selection to fix the type. This group of plants from a single parent has been given the name of centgener.1 Centgeners of a single strain are raised for three or more years, when, if found promising, all the seed, or as much as may be necessary, of the produce of the centgener, except the best one or more plants, is sown in small plats to test its adaptability under field conditions. If found satisfactory, the seed is rapidly multiplied and distributed among farmers and commercial seed growers. The plants reserved become mothers of centgeners with the hope of obtaining still further improvement.

1 Plant Breeding. By Willet M. Hays. U. S. Dept. of Agr., Div. of Veg. Phys. and Path. Bul. 29 (1901), p. 46.

V.

WHEAT.

109.

I. CLIMATE.

Conditions of Successful Wheat Culture.-The yield and quality of wheat, and hence its successful growth, agriculturally considered, depend mainly upon these six conditions: (1) climate, (2) soil (including fertilizers), (3) variety, (4) methods of cultivation, (5) liability to disease, and (6) attack of insect enemies.

IIO. Effect of Climate Upon Geographical Distribution.According to the tenth census seventy per cent of the wheat of the United States was grown where the average January temperature was below freezing; eighty-five per cent was grown where the average July temperature was between seventy and eighty degrees, and sixty-five per cent where the mean annual temperature was between forty-five and fifty-five degrees. Too much weight must not be attached to this, as the soil, particularly in respect to its ease of cultivation, has greatly affected the distribution of wheat. Most of the wheat of the world, however, grows in regions of cold winters, although there are some noted exceptions, as California, Egypt and India. Taking the world at large, and including both spring and winter varieties, wheat has a very wide climatic range. Its range of successful culture, also, seems to be constantly extending northward, whether through climatic adaptation or from other causes seems less clear.

III. Effect of Climate Upon Quality.-Localities having widely different climate and soil have their peculiar varieties, which differ somewhat in composition but much more in physi

cal characters, such as size, plumpness, hardness and color of grain, length and shape of spike and in length of straw. It seems to be quite conclusively demonstrated that these changes are more closely related to climate than to any other factor. (74) Some varieties of wheat, however, such as Fultz, have a very wide distribution.

Those localities which have extremes of temperature and rainfall, especially during the ripening period, generally have the hardest and reddest grains and the highest per cent of nitrogen, but are generally less plump and are smaller in size. Wheat of hot, sunny climates, with moderately dry weather during the latter part of growth, is brighter and makes better quality of flour the world over. The United States is particulary favored in this respect.

I12. Effect of Climate Upon Growth.-Seelhorst found that a high moisture content in the soil during early growth caused a larger number of spikelets per head, and that a high water content at time of heading increased the number of developed blossoms per spikelet.1

A cool, prolonged, but not too wet spring, followed by moderately dry sunny weather during ripening, is most favorable to the largest yield of best quality. The influence of the length of the growing period on the accumulation of plant food and consequently upon yield may be illustrated by assuming that a maximum crop requires twenty-four pounds of nitrates besides those already formed in the soil, and by assuming that throughout the growing season four pounds of nitrates per month are produced by the nitrifying agents in the soil. Six months of growth would be necessary to produce a maximum crop. If climatic conditions should force the crop to maturity in five months, there would not be enough nitrates to produce a full crop, unless the same climatic conditions influenced the production of nitrates in the soil. The loss of nitrates during wet seasons has been

1 Jour. Landw. 48 (1900), No. 2, pp. 165-177, pls. 2. (E. S. R. XIII (1902), 125.)

found to be greater and the amount taken up by the wheat smaller.

113. Accumulation of Soil Constituents at Different Stages of Growth. The wheat plant for its best development needs to have its early growth in the cool part of the year. A long period of growth consequent upon cool weather encourages tillering and gives better opportunity to get sufficient plant growth. Adorjan has shown that wheat takes up the greater portion of its food in the early stages of growth, stores it up, and draws upon it later for the development of the grain.1 (123)

At the Minnesota Station during two years the weight and composition of spring wheat was determined (1) at fifty days when it was eighteen inches high, (2) at sixty-five days when it was fully headed, (3) at eighty-one days when grain was in the milk, (4) at 105 days when wheat was ripe.

At the end of fifty days the plant had produced nearly onehalf its dry matter and nearly three-fourths its total mineral matter; when fully headed, sixty-five per cent of its dry matter and eighty-five per cent of its mineral matter. When the grain was in the milk the plant had produced ninety per cent of its dry matter and practically all its mineral matter. Nearly seventy-five per cent of the potash, eighty per cent of the phosphoric acid, and eighty-six per cent of the nitrogen was taken up in the first fifty days. The fiber was formed largely before the plant was tully headed; after the grain was in the milk a slight loss of fiber occurred in the plant. The starch stored up in the seeds was formed mainly during the last half of the period of growth.2

114. Winter Killing. In a country of cold winters it is better to have the ground covered continually with snow. Alternate freezing and thawing with the plant exposed to the wind is very destructive to wheat. Winter wheat kills in two ways, by freez

1 Jour. Landw. 50 (1902), No. 3, pp. 193-230. (E. S. R. XIV, 436.)

3 Minn. Bul 29, pp. 152-160