Circle Formation in Datura and Oenothera

Abstract

A summary is given of the analysis of chromosomes in Datura by means of extra chromosomal types, trisomic ratios, attraction between chromosomes and the formation of circles of 4 to 6 attached chromosomes in hybrids between selected races from nature. Several lines of evidence strongly support the hypothesis that in Datura races which induce circle formation in hybrids with a standard line have originated through segmental interchange between non-homologous chromosomes. Segmental interchange is believed also applicable to circle formation in Oenothera. The desirability is suggested of establishing a species of Oenothera with 7 pairs of chromosomes as a standard and of securing in this species primary, secondary, and tertiary (2n+l) types which might be used as testers for the study of the more complicated species characterized by large circles.