2. New Alleles of A. As previously noted (News Letter, 1941: 44) the gene A^b mutates spontaneously at a fairly high rate to a type resembling a^p. The mutants, identified by the pale aleurone effect, produce plants which like a^p produce both anthocyanin and anthoxanthin pigment. Nine of the mutants were checked for the dominant brown pericarp effect present in A^b and a^P, and all showed this effect also.

In plant color with B and Pl, the mutants were in general more deeply colored and more reddish than the standard a^p. They varied rather widely in degree of redness, ranging from a deep brown to a maroon shade approaching purple at maturity. The original mutants and various others which have occurred in later experiments with A^b, form an apparently continuous series between the two extremes. No mutant of A^b to a colorless aleurone type or to a type producing only anthoxanthin pigment in the plant has been found.

Four representative mutants were selected for further study, to determine whether the differences in expression were due to differences in the mutant alleles. The factor et, an X-ray induced chromosome 3 mutant, located 11 units distal to A, was combined with one of the mutants and also with standard a^p, and the phenotypic effects were compared in backcross progenies in which the various alleles could be compared in plant color (with B and Pl) in sib plants. The results show that the four mutants represent distinguishable alleles of A, each producing a mixture of anthocyanin and anthoxanthin pigments but differing in the relative quantity of anthocyanin produced. These are designated mahogany (A^b-m), cedar (A^b-c), chestnut (A^b-ch) and walnut (A^b-w).

The aleurone color of the mutant A^b's described, as identified in et-marked segregations, is paler than that of A^b or A, but not so pale as a^p. Seed separation may be made effectively in segregations against either A or a^p. There is also a recognizable difference in aleurone color between some of the mutant types, which sometimes is distinct enough for individual classification.

There are some interesting differences in the action of these pale aleurone mutants of Ab and the two pale aleurone mutants at hand which arose from other members of the A series. A^lt (News Letter, 1941: 46) is an ultra-violet mutant of A, which has a pale aleurone and reddish purple plant color, yielding anthocyanin and anthoxanthin pigment. A^w is a mutant of a, which occurred as a sector with pale purple anthers in a plant of a Dt B Pl R^r. It also produces pale aleurone and a reddish plant color, yielding anthocyanin and anthoxanthin. Qualitative tests show a distinct difference in the anthocyanin produced by A^lt and A^w, on the one hand, and by A^b-m, A^b-c, A^b-ch, A^b-w, and a^p on the other.

The pale A^b mutants, like a^p, show little or no difference in the aleurone color of homozygous seeds vs. seeds heterozygous for a. Both A^lt and A^w, in selfed ears of plants heterozygous for a, show clearly cumulative effects, the heterozygous seeds being distinctly pale and the homozygous seeds often being indistinguishable from full A.

In compounds among the pale A^b mutants and between these mutants and a^p, the plant color effect of the redder member is distinctly dominant, and in those cases in which aleurone color is distinguishable the darker type is dominant. A^lt produces a redder plant color than the A^b mutants or a^p, but the hybrid A^lt/a^p is intermediate, with a pronounced increase in anthoxanthin content. A^lt × a^p/a yields progeny of two very distinct types, the A^lt/a^p plants showing a distinct dominant effect of a^p on anthoxanthin production as compared with the A^lt/a sibs. This dominant effect of a^p is not evident in crosses with A or A^b, so far as the appearance of the plants is concerned. It is evident, however, in crosses with A^br, a Dt-mutant obtained by Rhoades, (News Letter, 1941: 6) which resembles A in plant and aleurone color but does not give red pericarp. In crosses of A^br × a^p/a there is a distinct diminution of red and increase of brown in the plant color of A^br/a^p vs. A^br/a sibs. A similar effect is shown by cedar, chestnut and walnut, the only A^b mutants tried in this combination. It is wholly absent in A^br × A^lt/a, the A^br/A^lt plants being indistinguishable from the A^br/a sibs.