In higher plants, the collapse of immature seed is a frequent cause of sterility following interspecific hybridization or crosses between diploid and its auto-polyploid plants.In one or both sides of interspecific reciprocal crosses : Galeopsis (Muntzing 1930(Muntzing , 1933 In the present paper, the embryological changes leading to the failure of seed development in the reciprocal crosses between B. chinensis and autotetraploid B. pekinensis are described. MATERIALS AND METHODSAutotetraploid B. pekinensis Rupr, cultivar. Chiifu-hakusai and diploid B. chinensis 1) 2)Contribution from the

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Cytogeneticalstudies on interspecific Fl hybrids between Brassica campestris and B. oleracea were carried out. Hybrid plants were produced by the culture in vitro of excised ovaries.Three types of Fl hybrids were obtained in the cross between diploid B, campestris, and diploid and autotetraploid B. oleracea. The first type plants had 19 chromosomes in root tip cells. The second type plants had 38 chromosomes which were presumably raised by spontaneous chromosome doubling during embryo development.The third type plants had 28 chromosomes which were produced by the cross, diploid B. campestris X autotetraploid B. oleracea. Mode of the chromosome configurations at the first meiotic division of the first type hybrids was 9II+1 (44.7%). Frequency of tri-, tetra-and pentavalents was 38.6%, 10.3% and 1.3%, respectively.Tetra-and pentavalents were observed for the first time in the present experiment.Chromosome configurations at meiosis of the second type hybrids were mostly 19II (86.7% and 80.0% in two plants).The mode of chromosome configurations at meiosis of the third type hybrids was 9II+10I (40.9%). Frequency of tri-and tetravalents was 38.1% and 1.2%, respectively. Tetravalents were observed for the first time in the present experiment.

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The cytological possibility of gene transfer from Sinapis pubescens to Brassica napus was investigated. Intergeneric hybrids between Brassica napus (2n = 38) and Sinapis pubescens (2n = 18) were produced through ovary culture. The F1 hybrids were dihaploid and the chromosome configurations were (0-1) III + (2-11) II + (5-24) I . One F2 plant with 38 chromosomes was obtained from open pollination of the F1 hybrid. Thirty-one seeds were obtained from the backcross of the F2 plant with B. napus. Five out of seven plants had 38 chromosomes, and the pollen stainability ranged from 0% to 81.4%. In the B2 plants obtained from the backcross of B1 plants with B. napus, 66.7% of the plants examined had 38 chromosomes. S. pubescens may become a gene source for the improvement of B. napus.