Soybean [Glycine max (L.) Merr.] growth and yield models depend on good predictions of phenological events such as flowering. Parameters for predicting flowering date of 12 cultivars were estimated for various development‐rate models. Date of flowering is predicted by accumulating a daily rate of development, which depends on night length and temperature, until a threshold is reached. Daily development rate is computed by a multiplicative relationship containing two functions: one for describing the variation in development rate with night length under optimal temperature and the other describing variation with temperature under optimal night length. There were 39 to 115 year‐location‐sowing date combinations for each cultivar, covering latitudes from 18°03′ to 45°25′ N lat. The downhill simplex method was used to estimate phenological parameters for each cultivar by minimizing the error sum of squares between observed and simulated flowering dates. Many formulations of the development‐rate model were compared. Linear‐plateau functions for both night length and temperature effects provided the best fit and yielded the most consistent results. The root mean squarerror between observed and simulated dates of flowering ranged from 3.45 to 5.28 d. Correlation coefficients between observed and simulated days from sowing to flowering varied from 0.987 to 0.841, with a decreasing trend from late toward early‐maturity cultivars. There was a clear difference among cultivars with respect to night‐length sensitivity, but a similaresponse to temperature.

Twenty‐two races of maize (Zea mays L.) and one selection of teosinte (Euchlaena mexicana Schrad) were grown under natural daylight in eight glasshouses where day/night temperatures were maintained from 15/10 to 36/31 C. Differences were found among temperatures and races in net photosynthetic rates, relative leaf growth rates, and leaf numbers. At low temperatures, high altitude races had relatively higher leaf growth rates and dry weights at harvest. At high temperatures high altitude races had relatively lower net photosynthetic rates. Leaf numbers increased with increasing temperatures.

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Soybean (Glycine max (L.) Merr.) genotypes varying in area per nodal unit (usually a trifoliolate) and maturity class were grown in plots at the University of Illinois experimental farm. Leaf CO2-exchange rates per unit area (CER) were measured under sunlight on intact plants. In addition to previously reported correlations with specific leaf weight and chlorophyll, CER was positively correlated with ribulose bisphosphate carboxylase (RuBPcase) activity, specific activity, and soluble protein, and was negatively correlated with area per leaf unit. The CER: chlorophyll correlation was destroyed by high CER values in 2 chlorophyll-deficient lines. CER values for 27 of the 35 lines tested fell within the range of those for isolines of cultivar Clark varying in leaf characteristics. The CER values were highest for fully expanded leaves during rapid pod fill. These results suggested that photoperiod (maturity) genes and genes for leaf area growth interact with genes controlling photosynthetic CO2-exchange to produce the major differences in CER values among soybean genotypes.

An attempt was made to develop general relationships quantitatively describing the effect of temperature on growth and development of a soybean [Glycine max (L.) Merrill] shoot. The time required for emergence and expansion of cotyledons and the appearance of the first pair of unifoliolates and of subsequent successive trifoliolate leaves on the main shoot was measured in controlled environments in a phytotron. For plants in greenhouses in midsummer, degree‐days per trifoliolate on the main shoot was fairly constant between 12 and 30 C. In the 30 C greenhouse the rate of trifoliolate emergence was much less in late fall than in early spring, suggesting that photosynthate supply was limiting in late fall. Increasing photosynthate supply by enriching the CO2 level around the plants in growth cabinets did not greatly affect the rate of trifoliolate emergence. This kind of data may permit the logical development of programs that simulate soybean growth.

Evolution of CO2 into CO2-free air was measured in the light and in the dark over a range of temperatures from 15 to 50°. Photosynthetic rates were measured in air and O2-free air over the same range of temperatures. Respiration in the light had a different sensitivity to temperature compared with respiration in the dark. At the lower temperatures the rate of respiration in the light was higher than respiration in the dark, whereas at temperatures above 40° the reverse was observed. For any one species the maximum rates of photosynthesis and photorespiration occur at about the same temperature. The maximum rate for dark respiration generally is found at a temperature about 10° higher. Zea mays and Atriplex nummularia showed no enhancement of photosynthesis in O2-free air nor any evolution of CO2 in CO2-free air at any of the temperatures.

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