5. Inbred stocks of tetraploid maize after four generations of selfing have good vigor, reasonably good uniformity, and in some cases an increase in fertility over the original parental tetraploid stock. Tetraploid strains of commercial yellow corn are being tested in cooperative bio-chemical and animal assay experiments to determine their vitamin A potency. Since the tetraploid yellow maize endosperm has six doses of Y rather than three as in the normal diploid yellow corn the vitamin A potency may be twice as great in the former as in the latter.