IN Trillium grandiflorum and other species of the same genus, cold treatment reveals differences between homologous chromosomes with regard to number and/or length of heterochromatic segments1. In our experiments, differences have been found in the B-, C- and E-chromosomes (Figs. 1, 2A). According to the number and length of these segments, the following types of chromosomes have been distinguished: B 1, B¼, C 1, C 2, E 2 and E 3 (where the suffixes give the number or length of the heterochromatic regions).