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 a1p 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 a1p 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.