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 a1p Dt Dt dt constitution is 3:2. The ratio for seeds of a1 a1 a1 Dt dt dt to a1 a1p a1p 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.