1936 年 7 巻 1-2 号 p. 131-142
1. Meiotic chromosomes of Tradescantia gigantea, after subjection to X-rays, tend to become contracted and clumped. Chromosomes which were irradiated during a premeiotic mitosis show extreme fragmentation, segmental interchange and, in mang Gases, a failure of pairing at the subsequent meiotic divisions.
2. Irradiation during the microspore metaphase or anaphase produces fragmentation, and the effect is immediate. Treatment during prophase also produces unbalanced fragments, translocations and occasional interchange rings; also an occasional balanced configuration.
3. When cells in the resting stage before the microspore division are treated with X-rays, the subsequent metaphases and anaphases show balanced abnormalities only. The fact that chromosomes irradiated at prophase or later stages show chiefly unbalanced fragments, while those which were in the resting stage when subjected to X-rays show only balanced abnormalities, is evidence that the chromosomes do not split until late in the resting stage.
4. No inhibition nor delay of division is found. Actively dividing cells are present continuously after irradiation in both meiosis and microspore divisions at the dosages used.
5. Evidence is offered to show that attachment points do not arise de novo and that the contraction of the chromosomes between prophase and metaphase is not due to the action of the attachment points.