Classification of development in maize (Zea mays L.) based on temperature is important because of the need in agriculture to determine the adaptability of genotypes to particular environments and to predict flowering dates for breeding purposes. An equation predicting the effect of temperature on rate of development of maize was obtained by measuring the rate of leaf appearance of six short‐season maize hybrids. The hybrids were grown in growth cabinets at constant day/night temperatures ranging from 10 to 35 C, in 5 C increments, with a 15‐hour photoperiod. Rate of leaf appearance was also measured on plants grown under 16 regimes of differential day/ night temperature. The predictive value of the temperature vs. rate of leaf appearance curve was compared with calendar days from planting to silking and accumulated heat units from planting to silking, calculated by both the Degree Days and Ontario Corn Heat Unit (OCHU) methods, using date of flowering for 22 hybrids grown during 3 years at four locations.Polynomial regression analysis of data for maize plants grown at constant day/night temperatures produced a cubic equation for rate of leaf appearance (leaves/day) vs. ambient temperature. This equation (Y = 0.0997 − 0.0360T + 0.00362T2 − 0.0000639T3) could be used to predict rate of leaf appearance in fluctuating temperature environments. For field‐collected data, the equation for rate of leaf appearance vs. temperature was superior to calendar days but similar to the Degree Days and OCHU methods in predicting dates of silking. Adjustment of the predicted time to silking by accounting for the effect of mean temperature during the first 30 days after planting on maximum leaf number (increase of 0.2 leaves/C increase in temperature) enhanced the precision of the derived equation in predicting date of silking.

At maturity a black closing layer develops in the placental region of corn (Zea mays L.). The suitability of this black layer as an indicator of physiological maturity was studied in four hybrids of a range in maturity. As viewed by the naked eye the layer developed in 3 days or less, and its appearance coincided with the achievement of maximum kernel dry weight. An examination of a wide range of genotypes indicated that the black‐layer formation is a common feature of commercial hybrids at maturity.An investigation of incompletely developed florets on partially barren ears or in the tip region of normal ears revealed black‐layer formation in those showing limited endosperm development. No black‐layer development was seen in nonfertilized or parthenocarpic florets.The cause and mechanisms of black‐layer formation are unknown. However, it is speculated that such development is related to assimilate movement into the developing floret.

In an attempt to explain plant-to-plant variation in dry weight of maize (Zea mays L.),

A Significant linear relationship was found among several corn (Zea mays L.) hybrids grown in 1966 and 1967 at Guelph, Ontario at several planting densities, between grain yield and effective filling period duration. Effective filling period duration (EFPD) is defined as final grain yield divided by the average rate of grain dry weight accumulation during the linear period of grain formation, and hence, is a relative measure of the length of the grain filling period. In each year yield differences among hybrids were more closely related to EFPD differences than to differences in the rate of ear dry weight accumulation. EFPD was unaffected by planting density. Results suggest that significant potential exists in corn for higher grain yields through a genetic extension of the length of the grain filling period.

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