The observed seasonal progression and annual variations in the cold resistance of field-grown winter wheats during a 6-year period at Lincoln, Nebr., together with associated variations in the environment, were utilized in a study of the more obvious weather factors contributing to field hardening. Two apparently distinct hardening stages were recognized in this work. During November and early December high daily temperature maxima in conjunction with high radiation appeared to be most conducive to hardening. High temperatures with low radiation or high radiation with low temperatures were least effective. High temperatures and radiation were effective only in increasing hardening under the influence of shortening days, however. Rather xeric conditions also appeared to favor hardening. This suggests that maximum hardening at this period results from a radiation-temperature balance reacting with day-length and drought influences to give maximum accumulation of organic reserves. Subsequent exposure to sustained low temperatures resulted in further progressive increases in hardiness for about 3 weeks. This low-temperature hardening reaction seemed always to effect maximum hardening for the season, the actual level apparently being determined by the efficiency and duration of the preceding growth-hardening stage. Controlled experiments showing a reduction in hardiness under the influence of reduced light intensity are reported.

The effect of fertilizers on the length of winter wheat heads was determined by measuring large numbers of heads taken from field plats in 1935, 1936, and 1937. The significance of mean differences was shown by analysis of variance. The use of Shepherd's correction for grouped data is illustrated. A statistical study of the number of heads necessary to make a representative sample is included. From the measurements and calculations, the following conclusions were drawn: 1. The unfertilized wheat produced longer heads in 1935 than did the fertilized wheat. In 1936 the condition was reversed. During both years, fertilizer applications greatly increased the number of heads per foot of row. The number of heads per foot of row on the unfertilized soil was almost twice as great in 1935 as in 1936. Accordingly it is concluded that when crowding is not a factor, fertilizers may be expected to increase the length of heads of winter wheat, but when the stand is so thick that the greater number of heads as a result of the fertilizer causes crowding, the length of the heads may be decreased. 2. Some fertilizers produced longer heads than did other fertilizers. 3. No differences in the results were obtained by using Shepherd's corrections for grouped data. 4. The data obtained from the measurement of 100 heads picked at random from each bundle showed that samples of 100 heads were not truly representative of the entire population. 5. When 700 heads were measured from each bundle, the significant differences were approximately the same as when all the heads were measured. The number "700" was also theoretically checked by calculating "N" from the formula for "t."

A uniform winterhardiness nursery has been grown in the Great Plains of the northern United States and in Canada since 1919. A summary of the data from 1930 to 1937 is presented. The object of the nursery is to obtain information on the relative winterhardiness of various varieties of winter wheat. Lutescens 0329, Buffum No. 17, and Minhardi are the most hardy winter wheats available. Some hybrid strains seem to combine quality of grain and yield with relatively high winterhardiness. In a general way the varieties studied may be placed in four groups for hardiness: Lutescens 0329 and Minhardi and a few hybrid strains in the hardy group; Minturki, Turkey (C.I. 6152), and Nebraska No. 60 in the mid-hardy group; Cheyenne, Kanred, Oro, and Kharkof in the slightly hardy group; and Quivira, Blackhull, Tenmarq, and Early Blackhull in the tender group. Between the extremes the varieties may be arranged in a gradually descending series from hardy to tender.