At meiosis inBrassica oleracea(cabbage and Brussels sprout),B. pekinensisand the relatedSinapis arvensisandEruca sativa, multivalents were common and numerous secondary associations of bivalents were detectable in all species from diplotene into metaphase. Quadrivalent formation in cabbage and Brussels sprouts usually involved an increase in chiasma frequency per cell and there is evidence that the potential quadrivalent frequency is limited, at least partly, by limited chiasma formation. Secondary associations are thought to represent lapsed multivalents. Extensive duplication of chromosomes (or of large chromosome segments), is therefore implied, and polysomic rather than diploid breeding behaviour should be expected for many gene loci.