We evaluated cold‐tolerance responses [measured by percentage emergence (30 days after planting), emergence index (an estimate of emergence rate), and seedling dry weight (sampled 42 days after planting)] of 34 maize (Zea may L.) inbred lines adapted to various latitudes in North America. Evaluations were performed in field experiments planted in early April at Ames and Algona, Iowa, in 1974 and 1976. Objectives of our study were: i) to assess genetic variability and breeding potential for improvement of cold tolerance within maize germplasm adapted to North America, ii) to study associations of cold‐tolerance traits with other plant traits (including grain yield), and iii) to examine relationships between geographical locations of origin and cold‐tolerance responses of inbred lines adapted to North America.We observed large amounts of variability for each of the three cold‐tolerance traits. Means ranged from 27.5 to 82.9% for percentage emergence, 20.0 to 24.0 days for emergence index, and 0.33 to 1.16 dg for seedling dry weight; respective heritability estimates were 0.85 ± 0.06, 0.72± 0.06, and 0.80 ± 0.06. Genotypic correlations among the three traits were high, suggesting selection for improved cold tolerance (as an aggregate of the three traits) should be possible. Environments and genotype ✗ environments mean squares were highly significant; therefore, evaluations of cold tolerance of maize inbred lines should be conducted in more than one environment.Correlations of all three traits with juvenile plant height and leaf number (measured in early July), 50% silk emergence, mature plant height, and grain yield usually were low. Thus, seedling cold tolerance was not associated with vegetative vigor of juvenile plants, flowering date, or mature plant height. Seedling dry weight, however, was significantly correlated with grain yield (r = 0.48**), indicating good seedling vigor was related to high grain yield.Cold‐tolerance response generally was not related to geographical location of adaptation; however, 9 of the 10 best inbred lines were adapted to the central latitudes of the U.S. Corn Belt. Inbreds from the northern and southern regions ranked average or lower for cold tolerance. The three best cold‐tolerant inbreds were B73, (V3 x B14)‐2‐1 (both from Iowa), and Mo 17 (from Missouri). Breeding populations developed from the best inbreds in our study should contain gene complexes for good cold tolerance, plus variable flowering dates, plant heights, and grain yields.

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69, 60, 49 and 22 percent for heading date, plant height, 100-seed weight, and yield, respectively. Petr and Prey (1966), using F2 plants in I5 oat crosses, obtained herit ability percentages (broad sense) of 33j 53j 5^, 61, 74, and 87 percent for number of panicles per plant, grain yield, panicle length, plant height, number of spikelets per panicle, and heading date, respectively. Both of these teams of researchers used variance components from spaced-plant data to calculate the herltabllity percentages. Mean heritability percentages (standard unit) for heading date In oat crosses were 62, 63, and 68 percent for the F^-F^, F^-F^, and F^-F^ comparisons, respectively, according to Prey and Horner (1957). Huang (1967) using data from replicated yield trials, found heritability values for oats of 76, 88, 93, and 72 percent for yield, 100-seed weight, heading date, and height, respectively. Using data from replicated oat trials grown in five testing environments, namely, low fertility, late planting, high productivity, low plant density and high plant density. Vela (1968) found heritabilities of 26, 31, 45, 28, and 42 percent, respectively, for grain yield, 71, 58, 60, 55, and 58 percent, respectively, for 100-seed weight, and 44, 55, 73, 64, and 71 percent, respectively, for plant height. Also from replicated trial data on oats, Wallace, Middleton, Comstock and Robinson (1954) found heritabilities of 43, 81, 61, 57, 40, and 83 percent for grain yield, seed weight, seeds per panicle, culms per plant, seeds per plant and height, respectively. Johnson and Frey (1967) found heritability values of 83, 33, 54, 68, 76, and 38 percent for height, plant weight, panicles per plot, splkelets per panicle, seed weight and grain yield, respectively when data were pooled over several environments.

The effects of fertility and moisture on root and shoot gorwth of oats (Avena sativa L.) were studied in potculture experiments. An experimental unit was a 75‐liter garbage can filled with low‐fertility Thurman sand, embedded 0.6 m deep in the soil. Forty‐eight can were covered with a plastic shelter to permit controlled moisture regimes. A factorial set of fertilizer treatments using two levels each of N (0 and 140 kg/ha), P (0 and kg/ha), and K (0 and 93 kg/ha) were applied at seeding time. At the initiation of stem elongation, wet (field capacity) and dry (wilting coefficient) moisture regimes were imposed across all fertility treatments. Traits measured on the plant tops were plant height, number of tillers, number of spikelets per panicle, dry weight and stem diameter. Weights were taken on roots extracted from 0.007‐m3 soil samples from the 0‐15‐, 15‐30‐, 30‐45‐, and 45‐60‐cm soil depths. The root and shoot growth responded more to fertilizer application when moisture was adequate than when deficient. Nitrogen and phosphorus, applied alone and in combination, gave more shoot and root growth than any other element or combination of elements. Shoot growth responded to added fertilizer in both the high and low moisture regimes, but root growth responded only in the wet regime. Leaching of the nutrients with surface irrigations caused maximum root response to N in the 30‐45‐ cm zone, but for P, which resists leaching, maximum response was in the 0‐15‐cm zone. Reduced root‐top ratios resulting from added moisture and fertilizer elements were due largely to large increases in top growth without concomitant increases in root growth. Increase in shoot weight from added fertilizer under the dry regime was not accompanied by increased root weight. We concluded that root response to added fertility could not be responsible for oat plants utilizing subsoil (30‐60‐cm depth) moisture to produce increased shoot weights.