1. Seed corn was selected and harvested in different stages of maturity ranging from about 20 days after fertilization until 6 weeks after maturity for a period of 7 years. Physical data covering moisture content, average weight per kernel, specific gravity, and test weight per bushel are given. 2. Laboratory germination tests showed approximately 10% dead kernels in the first and last groups selected. In the other groups germination was much better. Seedling vigor was much better in the more mature stages than in milk and late milk stages. 3. Seed infections with Fusarium moniliforme, Diplodia zeae, and Gibberella saubinetii were present in the milk stage and with the first two organisms mentioned, the percentage of infection increased progressively until the mature stage. There was an important increase from tbe dent to the mature stage, but there was on the average no significant increase after the mature stage. Cephalosporium acremonium was entirely absent in the first two groups selected, but appeared in groups harvested later. Susceptibility to scutellum rot was greatest in the most immature stage and diminished progressively with later stages. 4. Field stand varied directly with the vigor of the seed planted even though only ears showing 100% germination in a laboratory test were used. The stand was allowed to remain unaltered and the acre yield varied directly with the stand, the mature stage producing the best stand and yield. Corn selected at husking time was as good as that harvested as soon as mature in some years, but not in others. 5. Seed inoculation at planting time with several fungi capable of causing seedling disease in all cases had the greatest effect on immature seed. 6. Ear rots were in some seasons apparently most severe in plants grown from immature seed.