1.
P. bracteata LINDL. has 14 diploid chromosomes, which make 7 bivalents in the meiotic phase of the PMC. The meiosis in the PMC occurs quite regularly and good healthy pollen grains are formed. Though it shows high sterility when selfed, the crossing
inter se results in good seeds. The genom will be denoted by B.
2. Supposed natural hybrid between
P. orientale and
P. bracteata or its derivative (No. 41-8) shows similar behaviour of chromosomes in the meiotic phases in PMC to that of artificially raised
P orientale×
P bracteata and its reciprocals, but the gametes in the latter are highly sterile while those of the former show a higher fertility.
The somatic chromosome number in these plants is 28, though in some cells of No. 41-8 plant a small fragment chromosome was found in the meiosis. In meiosis of PMC 12, closely jointed, and one loosely jointed, bivalents, and 2 univalents were observed. These univalents divide or not in the lst meiotic division. Irregular behaviour of the chromosomes in the ist and 2nd divisions, namely the formation of diads, triads, extranuclear chromosomes, small Pollen grains, was observed in addition to good healthy looking tetrads.
3. It is expected that a triploid will be obtained by crossing No. 41-8 with
P. bracteata, a pentaploid by crossing
P orientale with No. 41-8, and an octaploid by selfing No. 41-8.
4.
P Orientale is a hexaploid plant, and three genoms in its haploid are dissectable, each consisting of 7 chromosomes. Two of them form 7 bivalents in the meiotic phases of the F
1 plants of
P orientale and
P. bracteata, and also in
P. somniferum×
P orientale and its reciprocal. Six chromosomes in a genom of
P. orientale make 6 bivalents with 6 chromosomes in the genom B.
5.
P. orientale may be an autohexaploid, a closely related diploid plant with
P. bracteata, but the determination has been postponed until more experimental data are at hand.
6. There were no homologous chromosomes between
P. orientale and
P. somnifelum nor between
P. somniferum and
P. lateritium. In closing the writer wishes to express her hearty thanks to Prof. K. Fuazi by whose suggestion these studies were started, for his valuable advice throughout the course of the work. The expense of carrying out this study was partly defrayed out of a grant from the Foundation for the Promotion of Scientific and Industrial Research of Japan, to the authorities of which the writer's thanks are due.
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