(1) The author got a tetraploid chinese cabbage by means of Colchichin method, and tested the fertilities of this plant and the hybrids crossed with a few
Brassicas.
(2) The fertility of the tetraploid plant was very poor in self-pollination. In natural-pollination, fertility was also poor in the cross with diploid.
B. chinensis, but it was rather high in the cross with
B. napus or
B. jnncea. This seems to show that hybrid is more easily obtained in the cross between those which have nearer numbers of chromosomes than between those which have the same gemini.
(3) Fertility of the hybrids crossed by
B. napus was very distinct from that crossed by
B. juncea. The former had the fertility about 8 times as large as the latter in seed numbers obtined from 100 flowers. Affinity of
campestris' genom to
oleacea's genom is higher than the former to
nigra's genom, and this seems to cause that distinction.
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