The genetics of ‘corky’. II. Further studies on its genetic basis in relation to the general problems of interspecific isolating mechanisms.

1. Further data are presented in support of the writer's previous finding (Stephens, 1946) that the Corky complementary genes in New World octagons are not located at independent loci. Comparison with analogous, more critically analyzed eases suggests that the complementary genes are pseudo-alleles. 2. The Corky complex is located on the same chromosome in the D genome as the Crinkle/Contorta series, and no critical evidence of crossing-over between them has yet been obtained. It is suggested, that the Crinkle/Contorta series may also have a pseudo-allelic basis. 3. A re-examination of The complementary Crumpled mechanism in Asiatic cottons (A genome) shows striking genetic and phenotypic similarity to the Corky mechanism, and suggests that the two complexes have a similar pseudo-allelic basis. In spite of their close similarity there is, as yet, no critical evidence that Crumpled and Corky are duplicates. 4. A survey of similar complementary mechanisms in Crepis and Triticum/Aegilops hybrids in comparison with Crumpled and Corky suggests that they all may have a similar basis, and may have played a part in interspecific isolation during one phase of their respective evolutionary histories. Reasons are given for the opinion that complementary isolating mechanisms are more likely to be built up from pseudo-allelic complexes than from independent loci.