抄録
1. In this investigation external characters and maturation division in P.M.C-s of back crossed hybrids raised from Haynaldia villosa×Secale cereale F1 with S. cereale were studied cytologically.
2. 12 individuals of back crossed hybrids were raised by crossing 2073 flower of H. villosa×S. cereale F1 plants with the pollen of S. cereale, the percentage of which is 0.58%.
3. The back crossed F1 plants resembles morphologically rather to rye than the H. villosa ×S. cereale F1 plants (Fig. 3 and Table 1).
4. The number of chromosomes of the back crossed F1 plants was 2n=21 and 20. In either of these numbers, 7 chromosomes seem to have come from S. cereale and the remaining 13-14 chromosomes from H. villosa×S. cereale F1 as the mother plant.
5. The number of bivalents in one P.M.C. at 1st maturation division was 1-8 in the case of having 2n=20 chromosomes. But in the case of those having 2n=20 chromosomes, the number of bivalents has voried 1-7 or 0-8 according to individuals (Table 2 and 4). Those bivalents of the former case i.e., of the individuals having 2n=21 chromosomes, appears to result from autosyndesis between the chromocomes of R genom of S. cereale and between those of V genom of H. villose respectively. And in the latter case of those individuals having 2n=20, in addition to the bivalents due to autosyndesis, a bivalent resulting from allosyndesis between chromosomes R and V genoms seems to exist, though very rare.
Some of these bivalents were observed as the univalents resulting from early splitting. Trivalents and tetravalents, in addition to the bivalents, were observed in rare cases.
6. From the result obtained in the study on the maturation division in P.M.C-s, the constitution of genoms of these back crossed hybrid F1 plants seems to be VRR in the plants having 2n=21 chromosomes and VRR-1 in that having 2n=20 chromosomes.
7. The chromosomes were distributed to the poles at ana-telophase in 1st maturation division is almost equal numbers.
8. The back crossed F1 plants were completely sterile in male and female gametes.
9. As abnormal cases of P.M.C-s in maturation division, the giant P.M.C-s having 30 or more nuclei (or having chromosomes corresponding to the numbers of nuclei) were observed frequently in these back crossed F1 plants. These giant P.M.C-s seem to have resulted from repeated nuclear divisions without cell divisions.
