Abstract
1. A spontaneous haploid (2n=24) was found in an F3 family of the crossNicotiana Tabacum (Amersfoorter)×N.Tabacum atropurpurea. 2. The plant was a typical dwarf and appeared to be completely sterile. 3. At diakinesis and first metaphase 0,1 or 2 bivalents occurred, the average number per cell being 0,63 at diakinesis and 0,43 at metaphase. 4. First metaphase shows the univalent chromosomes scattered all over the spindle. 5. During first anaphase most chromosomes pass to the poles without division; in many cells, however, a few chromosomes between the polar groups divide equationally. 6. Out of 436 interphase cells 6 (1,38%) showed a restitution nucleus. The very few normal pollen grains probably arise from such restitution nuclei. 7. The literature on haploidNicotiana Tabacum is discussed with respect to homologous and non-homologous pairing, bivalent formation, and the occurrence of first metaphase plates consisting of bivalents or univalents.
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