1. The dominant Dt gene has been reported (1936) to produce dots of aleurone color on a₁-tester seeds. The nature of the interaction between Dt and a₁ was unknown at that time. It has now been established that Dt causes a₁ to become unstable and to mutate at a rate thousands of times greater than normal. Mutations of a₁ in the presence of Dt can be detected in aleurone, husks, and leaves i.e. plant color, and pericarp tissue. Recessive a₁ mutates to the A₁ allele a thousand times as frequently as to the a₁^p allele. There is no chromosome abnormality present in the Dt line. The a₁ gene is in chromosome 3 while Dt may belong to chromosome 9. Mutations of a₁ to A₁ or a₁^p occur late in development in all tissues. It is not possible, at least by the writer, to reconcile these data with any of the hypotheses advanced by Schultz, Stern or Patterson to explain variegation. They seem, however, to agree with Demerec's conception of increased mutability being caused by a chemical or physiological condition produced in the cell. Recessive a₁ is highly stable in the presence of dt. The Dt gene is specific in its effect on a₁. No other recessive locus including a₂, c, r, lg₁, wx and su is affected. A dominant modifying gene reducing the frequency or rate of mutation has been isolated. There is some evidence of a recessive gene affecting the time of mutation.