Five maize (Zea mays L.) hybrids, FS854, B73 x Mo17, B84 x Mol7, B73 x B77, and P3382, grown under field conditions, were sampled at intervals during the grain-filling period. Plants were subdivided into stalks (including sheaths), leaves, and kernels. These parts were assayed for dry weight, reduced nitrogen, and extractable nonstructural carbohydrates. The duration and rates of net nitrate reduction and photosynthesis were approximated by the changes over time in the accumulation of reduced nitrogen and dry weight by the plant (total, above ground), respectively.Data on the accumulation of reduced nitrogen and dry weight by the plant show that decreases in nitrate reduction preceded (in time and extent for four of the hybrids and in extent for FS854) decreases or cessation of photosynthesis. FS854 continued to accumulate reduced nitrogen and dry matter throughout the grain-filing period.The patterns of change in stalk carbohydrate and reduced nitrogen during the early stages of ear development show the stalk serves as a storage reservoir and that these reserves were remobilized during the final stages of grain development. The marked increase and maintenance of dry weight and carbohydrate content of stalks until 34 days after anthesis, shows the capacity of the leaves to produce photosynthate through the first half of the grain-flling period exceeds the needs of the ear and/or the transport system. In contrast, stalk nitrogen content shows a slight increase up to 12 days after anthesis and decreases continualy thereafter. Leaf nitrogen was lost continuously throughout grain development. The potential capacity of the plant to supply newly reduced nitrogen was inadequate to support initiation and early development of the kernels without remobilization of vegetative nitrogen. Of the two hybrids having delayed leaf senescence, FS854 with its initiaDly higher concentration and content of reduced nitrogen in the stalk, initiated and developed a bigger ear than P3382, which had lower levels of stalk nitrogen. Three of the five hybrids had 'near linear' rates of accumulation of kernel dry weight, whereas none of the hybrids had linear rates of gain in kernel nitrogen. Al hybrids had maximum or near maximum rates of gain of kernel nitrogen between 26 and 34 days after anthesis and a marked reduction (41-52%) of rates in the folowing sampling interval. These decreases are concurrent with decreases in rates of nitrate reduction (nitrogen accumulation) by the whole plant for four of the hybrids and with decreases in remobilization of nitrogen from the vegetation of FS854. Data for the ratio of rates of accumulation of dry weight/reduced nitrogen by the kernels versus time after anthesis, show that the accumulation of dry weight and reduced nitrogen are independent of each other. The variations in the ratio values appear best related to variations in the availability of nitrogen from the vegetation.The high carbohydrate content of maize grain (approximately 'Supported by Allied Chemicals. 80%o carbohydrate versus 1...

Seed growth and development is an important part of the yield production process in grain crops. Experiments were conducted in the field for 2 yr to determine the seed growth characteristics of soybean [Glycine max (L.) Merr.] genotypes that varied widely the duration of seed fill. Fifty‐nine genotypes were grown in 1982 on a Donerail silt loam soil (fine, mixed, mesic Typic Argiudolls) and measurements of seed growth rate (SGR), final seed size (FSS), and effective filling period (EFP) were made. The 59 genotypes exhibited a wide range in SGR, FSS, and EFP. Although SGR and FSS were significantly correlated (r = 0.76**, significant at the 0.01 probability level), subsets of genotypes could be identified that exhibited a wide range in FSS with no variation in SGR. In 1983, seven genotypes (six plant introductions and one cultivar) were selected, on the basis of the 1982 data, to have a relatively similar SGR but a wide range in FSS and EFP. These genotypes were grown on a Maury silt loam soil (fine, mixed, mesic Typic Palendalfs). Fruit samples were taken at weekly intervals to characterize seed development. Cotyledon cell numbers were measured on selected cultivars in 1982 and 1983. For genotypes that differed in EFP, the patterns of dry matter accumulation and seed moisture changes with time were similar to those previously reported. The number of cotyledon cells per unit mass of seed decreased as FSS increased indicating that differences in cell size were associated with the differences in seed size in these genotypes. These data indicate that variation in FSS among genotypes can be associated with either variation in SGR and/or filling period duration.

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