The primary grain in oat spikelets is larger than the secondary grain. Oat genotypes were grown to determine the effects of planting primary and secondary grains separately on vegetative and reproductive growth. Plants from primary seeds had higher yields than those from secondary seeds. The advantage was associated with earliness of heading. It was concluded that increased seed uniformity would be advantageous. / Reductions in panicle size by removal of all primary grains and some secondary grains indicated that secondary grains have more growth potential than observed in untreated panicles. However, secondary grains in the treated panicles did not achieve weights equalling those of primary grains in the untreated panicles. / Variation in primary:secondary seed weight ratios was found among experiments. The variability was attributed mainly to instability of secondary grain weight. / The inheritance of secondary grain weight and of the primary:secondary seed weight ratio was studied at two locations. For both traits, additive and non-additive genetic effects were evident. Dominant gene action was relatively unimportant, suggesting good potential for improvement through pure-line breeding.

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