クルマバツクバネソウの還元分裂を低温または高温の条件で進行させ, その第一中期における染色体の形態的変化を観察して次の結果をえた.
1. 0°C の低温処理では真正染色質部分と異質染色質部分に相違が現われた. 前者はラセンの直径の増大に伴う長さの短縮が, 後者はラセンの直径の減少に伴う長さの伸長が見られた. すなわち, 還元分裂染色体においても体細胞染色体と同様, 低温処理によって真正染色質部分と異質染色質部分を区別できることを実証した.
2. 20°Cの高温処理の場合には染色体は対照区のものよりやや伸長する傾向が見られたが, 真正染色質部分と異質染色質部分の相違は現われなかった.

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Growth and callus formation were observed using pith tissues of Nicotiana tabacum “Bright Yellow” (2n=48) and N. alata (2n=18) which were cultured on a basal medium or basal medium plus IAA, kinetin, or both.
In “Bright Yellow”. chromosome aberrations and the formation of tracheid-like cells were observed in subcultured callus tissues, but no organ formation was found through 7 successive subcultures.
In callus tissue of N. alata, numerous roots were formed when only 2.0mg/l IAA was added to the basal medium. On the medium with 2.0mg/l IAA and 1.0mg/l kinetin, the callus tissues produced many buds but no roots. Callus tissues forming roots were easilly brought into budding by transplanting them onto the medium for bud formation. On the other hand, callus tissues forming buds produced roots when transferred to the basal medium supplemented with yeast extract. From those callus tissues were obtained restored plants (disomic or trisomic), which developed into maturity.

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1. Seventy-six loci of recessive lethal genes on the second chromosome, isolated from natural populations of Drosophila melanogaster, were determined by using three dominant marker genes (Sp, Bl, L).
2. The distribution of 76 lethal loci was not random along the genetic map; 19 loci being in the left (from 0 to 40 unit), 38 loci in the middle (40-70) and 19 loci in the right (70-108) region.
3. Other eighteen lethal chromosomes seemed to have multilocus-lethals (two or three lethal genes on a chromosome).
4. Twenty-six loci of the spontaneous lethal genes, which had not been through the force of natural selection, were also determined by the same method. Their distribution on the chromosome was apparently at random; 8 loci being in the left, 7 loci in the middle, and 11 loci in the right region.
5. The apparent non-random distribution of the natural lethal genes is difficult to understand in view of the location of most persistent lethal genes near the centromere; it is more likely that loci liable to natural mutation are distributed non-randomly on the second chromosome.
6. Six second-chromosome inversions were found to be associated with the natural lethals. No inversion could be detected in association with the spontaneous lethals. The role of inversions in natural populations are discussed from the view-point of maintenance and occurrence of lethal genes.

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The influence of mitomycin C, chloramphenicol, ATP and various nucleosides on the yield of X-ray-induced chromosome aberrations was examined with the ovular tissue cells of Trillium kamtschaticum.
Mitomycin C and chloramphenicol both brought about a significant increase of chromosome aberrations. ATP efficaciously reduced the aberration yield, thus indicating that the healing of chromosome lesions involves metabolic processes requiring energy supply. Simultaneous application of one, two or three kinds of nucleosides did not bring about any significant decrease in aberration frequency. Application of the nucleoside mixture containing the base components of DNA significantly decreased the aberration yield, but in the case of simultaneous application of four nucleosides of RNA components the frequency of aberrations in total did not reduce with a statistical significance, though there was seen a tendency that the aberration yield is reduced by the treatment. When the mixture of four nucleosides (adenosine, guanosine, cytidine, thymidine) or ATP were simultaneously administered with mitomycin C or chloramphenicol, the favorable action of the nucleoside mixture and ATP on the rejoining of chromosome breaks was completely arrested by these metabolic inhibitors.
The experimental results suggested that both the syntheses of DNA and proteins are involved in the rejoining of X-ray-induced chromosome breaks, but do not necessarily give the clear-cut evidence as to which of them is more directly participated in the rejoining process.

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The combination experiments of X-irradiation with some mixture solutions of various nucleotides were undertaken with the chromosomes of the ovular tissue cells of Trillium kamtschaticum.
Thymidine triphosphate did neither reduce nor increase significantly both frequencies of simple and rejoined breaks produced by X-rays. An equimolar mixture solution of three deoxyribonucleotides of dATP, dGTP and dCTP did not also result in any significant difference in the frequency of breaks from the X-ray control.
When the four components commonly found in DNA or RNA were supplied as the form of nucleoside or nucleotide, there was a tendency toward the decrease of the frequency of breaks. The significant decrease in the frequency of simple breaks from that of the X-ray control was recognized in the three cases of (dATP+dGTP+dCTP+dTTP)+, (dATP+dGTP+dCTP+UTP)+, and (ATP+GTP+CTP+dTTP)+X-ray treatments.
These results suggest the involvement of DNA synthesis in the process of reunion of X-ray-induced breaks, at least in restitution to restore the original continuity of chromosomes.

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The present X-ray fractionation experiments with PMCs of Trillium kamtschaticum could indicate that two distinct types of chromosome breaks are induced by X-irradiation, as judging from the time periods until the onset of rejoining. One of them was the breaks of which rejoining begins immediately and is complete within about 1 minute, and another was those which do not initiate rejoining until 30 to 60 minutes after irradiation. The possibility that the former is the breaks of ionic nature and the latter is of covalent nature was discussed.

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An albino mutant (KU No. 1246) of sand oats was grown in several culture media or under different temperatures, and chlorophyll formation was observed in their leaves.
Higher concentrations of glucose (0.3-0.5M) in the basal medium resulted in a greater production of chlorophyll when albinos were grown at 21°C. On the other hand, albinos cultured under higher temperatures (21-30°C) also produced a larger amount of chlorophyll. However, the chlorophyll content of albino leaves was less than 10% of that of normal greens grown under the same conditions.
A similar increase of chlorophyll in albino was also observed in the media containing 0.1M glucose and a high concentration of mannitol (0.3-0.4M). Thus, it is presumed that a part of the effect of glucose might be of providing the medium with a high osmotic pressure which could be substituted by mannitol.
A vitamin-mixture and indole-3-acetic acid seem to be slightly effective on the chlorophyll formation in the albino plants.

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