Abstract
1. A number of varieties of Nicotiana Tabacum, which were long cultivated in Japan, was examined karyologically. The gametic number of chromosomes found in these varieties were 24, except only a variety of“Okusa-ha”.
2. As the behaviour of chromosomes in the meiotic phase of the variety“Okusa-ha”was somewhat irregular, that determination of the exact number of chromosomes was difficult. Most of the pollen mother cells had 24 gametic number of chromosomes, while in some of the pollen mother cells an abnormal number of chromosomal elements was found, as for instance, 30, 36, 42, 48, etc.
3. “Hatano-ha”, a mutant of N. Tabacum var. petiolata, is characteristic in the increased number of leaves. But in this experiment the chromosome number of mutant was n=24 and their behaviour in division were the same with those of the original forms.
4. In pollen mother cells of N. glauca, a newly introduced form, 12 gametic chromosomes were counted, which confirms the result obtained in the same species by GOODSPEED.
5. The pollen mother cells of the F1 plants of N. Tabacum var. petiolata, “Ibusuki-ha”(n=24)× N. glauca (n=12) contained both univalent and bivalent chromosomes in the meiotic stage. The number of the bivalent chromosomes varies from one to twelve. The method of syndesis seems to be allosyndetic. The behaviour of chromosomes in meiotic division was irregular.
6. The hybrid above mentioned is self-sterile. But a few nonviable seeds were obtained in the case of F1×N. glauca, although no seed was obtained in the reciprocal cross.
