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SUMMARY
The present paper describes the presence of 1–2 B-chromosomes in 8 cultivated populations of Aster novae-angliae L. The B's do not pair with the A-chromosomes but they pair between themselves and form a small bivalent. While the B's have no effect on plant phenotype and plant fertility they significantly affect the size of A-chromosomes. Thus while average total complement length of A-chromosomes of cells with B's was 36.7μ it was only 27μ in cells without B-chromosomes. It is suggested that a similar effect in the germ line accounts for the higher chiasma frequency observed in the pollen mother cells in the presence of supernumeraries.