Interspecific Hybridization in Brassica : III. The Cytology of F. Hybrid of B. Cernua and B. Napella

From the foregoing description it is clear that the FI, hybrids B. cernua x B. Napella present 10II + 17I chromosomes in their heterotype metaphase. Thus I can say now on the basis of actual observations that the synaptic union occurs in ten pairs of chromosomes, and never in the remaining ones. I might further say that only those of cernua and Napella having a strong affinity to chinensis ones make synaptic union between them, when brought together by means of hybridization. The behaviour of bivalent and univalent chromosomes throughout the meiotic process is entirely similar to that observed in the interspecific Brassica hybrids reported in my previous papers (4, 5, 6). In short, the hybrid also belongs to the Pilosella type, and approximates the Drosera type. The same kind of chromosomal behaviour has also been observed in the hybrid of Triticum vulgare and Aegilops cylindrical (7, 2). The facts described in my previous papers and in the present one suggest the hypothesis that there are three dissimilar chromosomal sets, namely a, with ten chromosomes, b, with eight chromosomes, and c', with nine chromosomes, and that there is no affinity between chromosomes belonging to the different sets. All species with ten chromosomes contain only the set a, and B. cernua and B. juncea2 contain only the set a and B. cernua and B. juncea2 contain the set a and b, while B. Napella contains the set a and c'. If B. Napella is derived from the Mediterranean species B. napus, the latter should contain the set a and c, where c is composed of eight chromosomes similar to those in c', but dissimilar tn those in b which is found in Asiatic B. cernua with eighteen chromosomes. The chromosome complements in B. oleracea and in Raphanus sativus are both composed of nine chromosomes, but they prcbably belong to sets entirely different from each other (3, 1). There is no affinity between the Raphanus-set chromosomes and the chromosomes belong to the set a or b (1). The oieracca-set is now under investigation.