3. The study of the factor interaction of a₁ and Dt has been continued (see maize letter of November 24, 1934). On the basis of rather extensive counts the ratio of the average number of dots on seeds of a₁ a₁ a₁ Dt Dt dt to the average number of dots on seeds of a₁ a₁ a₁^p Dt Dt dt constitution is 3:2. The ratio for seeds of a₁ a₁ a₁ Dt dt dt to a₁ a₁^p a₁^p Dt dt dt constitution is 3:1. Since in the comparisons the Dt gene is held constant while the dosage of a₁ varies, it is apparent that the effect of increasing the dosage of recessive a₁, as indicated by the average number of dots, is an arithmetic one. In reciprocal crosses between two closely related lines (a₁ a₁ dt dt x a₁ a₁ Dt Dt) the ratio of the average number of dots on seeds of Dt Dt dt to seeds of Dt dt dt constitution was 4:1. Some data have also been obtained on the number of spots of Dt Dt Dt constitution. These data indicate that the effect of increasing the dosage of Dt may be geometric.