Maize (Zea mays L.) grain yield depends on the number of kernels per plant that reach maturity. In this work, associations between floral development within the ear and final grain number of maize hybrids differing in prolificacy were studied under nonstress conditions in Argentina. In one experiment at Rojas (34 ° 08'S), four hybrids were sown on four dates, at 8 plants [m.sup.-2] during 2 yr. Ears were observed at silking to determine the variation in the number of spikelets per ear. In the second experiment at Salto (34 ° 33'S), a nonprolific (DK638) and a prolific (DK 3S41) hybrid were sown at 7 plants [m.sup.-2] on three dates. Ears were examined between the three-leaf stage and silking + 12 d to determine floral differentiation. No sowing date effect was evident for the number of spikelets per ear, the number of rows per ear, or the number of spikelets per row, but hybrids differed for these characters (P [is less than] 0.05). During active spikelet initiation, spikelet number in apical ears increased at a rate of 0.13 (DK 638) or 0.17 (DK 3S41) spikelets per row per ° Cd. At silking, almost all spikelets along a row in the apical ear had completed floral development in both hybrids, but the prolific type showed less spikelet abortion in the apical ear and a more synchronous development between ears. Kernel number per ear was independent of floral development stage at silking, but was related to the rate of ear growth (in length) around silking. These results suggest that assimilate partitioning to the ear during this period is critical for kernel set., Grain yield of maize is mainly dependent on the number of kernels per plant that reach maturity (Cirilo and Andrade, 1994a; Otegui et al., 1995b); this yield component is very [...]