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first killing frost in the fall for different parts of Nebraska are shown in the accompanying map.

     It is rather self evident that the farther north and west one goes in the state, the more subject the corn is to freezing injury. Progressing in these directions, the corn does not only grow more slowly because of a lower number of total heat units during the growing season, but also because of the shorter season.

      During three years, corn differing in moisture content has been subjected to freezing at various temperatures under control conditions. The results are given in Table II.

      The temperatures used ranged from 32°F to -5°F and were inclusive of any low temperature which might occur during the fall or early winter. A rather close correlation is found to exist between the amount of moisture present in the kernel and the amount of freezing which may be endured without injury. To illustrate: When corn samples differing in moisture content were subjected artificially for 24 hours to a temperature ranging from 32° to 28°F, the following results were obtained: Corn containing less than 25 per cent moisture germinated 100 per cent; 25 to 35 per cent moisture greminated (sic) 80 per cent; 35 to 45 per cent moisture germinated 80 per cent; 45 to 55 per cent moisture germinated 33 per cent; 55 to 65 per cent moisture germinated 28 per cent; 65 to 75 per cent moisture germinated 1 per cent; and 75 to 85 per cent moisture was entirely dead. This range in temperature represents that of the first killing frosts in the fall but was of longer duration than occurs under natural field conditions.

      In the case of immature corn freezing injury at a given moisture content increases as the temperature lowers. For example, for corn

FIG. 1--Vertical section of kernel of dent corn.
FIG. 2--Cross section of kernel of dent corn.
FIG. 3--Growth after 35 hours favorable germination.
FIG. 4--Growth, after 55 hours germination showing secondary roots.

containing 25 per cent moisture, the germination percentages were respectively 100, 96, 88, 47, and 0 per cent when exposed for a 24-hour period to temperature ranges of 32° to 28°F., 24° to 20°F., s6° to 12°F., 8° to 4°F., and 0° to -5°F.

      Dry corn containing 10 to 54 per cent of moisture will not be injured by any amount of winter freezing. Air dry corn with a moisture content of 10 or 12 per cent will withstand the freezing temperature of liquid air or 190^o F below zero. On the other hand corn with 60 per cent moisture may be killed by prolonged exposure to barely freezing temperatures.

      There may be variation in the moisture content of kernels on the same ear, which will account for partially impaired germination of an ear. In 1915 as much as 16 per cent variation was found in the moisture content of such kernels.

      The data in Table III show such variation.

      The embryo, or germ, of the corn kernel dries out more slowly than the remainder of the kernel as is shown in Table IV. In corn selected at husking time, which contained about 25 per cent moisture, the germ had a considerably higher moisture content than the balance of the kernel, while when it had become practically air dry it contained somewhat less moisture.

      Beginning with the day of the first killing frost in the fall of 1917, October 8, corn samples representing seven distinct degrees of maturity were selected from an Experiment Station field of Hogue's Yellow Dent Corn at four consecutive intervals during the fall and winter, and the progressive effect upon the germination of the seed was noted. The selections as to soundness were based entirely upon the outward appearance and solidity of the ears. Moisture determinations were made at the time of gathering by compositing portions of every ear in each group. The balance of the ears were tested for germination later in the winter after becoming well cured. Before testing, the germination was estimated for all ears in each group by examining the color of the germs. The results are given in Table V.

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      *The first selection was made after the first killing frost which occurred in the early morning of October 8.

      But little injury resulted from the first killing frost to corn containing less than 47 per cent moisture, even tho the temperature fell as low as 24^o F. and continued for a period of nine hours. On the other hand the prolonged freezing weather following in October and November materially injured the bulk of the corn. Most of the damage occurred prior to November 19. Following this, corn stand-

 

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