Frost resistance of nine different varieties of the tea plant was studied in different ways mainly as regards to seasonal change. The following results were obtained. Frost resistance of nine varieties tested is ranked in the following order ; Yabukita, U-22 (triploid) and U-24 (triploid) are very resistant ; Y-1, Y-3, Y-6 and Benihomare moderately resistant ; X-10 and X-12 are slightly resistant. Frost resistance increased with the decrease of water content in leaves, and simultanuously with the increase of osmotic concentration in the leaf cell. Frost resistance increased also with the increase of sugars content. Varieties with leaves containing more total sugars in midwinter were more resistant, although varieties with leaves containing more reducing sugars were not always more resistant. Tannins content in leaves had no definite relation with frost resistance. The increase of frost resistance has no direct relation with the content of total nitrogen and water soluble nitrogen, while water soluble protein increased with the increase of frost resistance, and varieties which contain more water soluble protain in leaves in midwinter are more frost-resistant

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The present paper describes some cytological investigations regarding meiosis in PMCS and the number of chromosomes and fertility of G₂-G₄ plants (2nd to 4th generation) that originated from artificially synthesized forage rape (B. napus). It was shown that chromosomal behavior of the progenies from surely-selfed C0-1 (Chinese cabbage "Shlgatsu" x cabbage "Successron") was very irregular and that of the progenies crossed with commercial varieties of rape (Norin-16 & France-12) was considerably stable, through observations on meiosis in PMCS of many plants with 2n=38 or 38 ± X(Tables 1, 2, 3, 4, 8, and 9). Self fertility of the progenies from surely-selfed C0-1 was very poor, but that of the progenies crossed with commercial varieties of rapes was relatively high. In the progenies of surely-selfed C0-1, cross fertility with commercial varieties was higher than self fcrtility (Tables 6 & 11). Thus, the author believes that crossing between artificially synthesized and commercial Varieties of rapes is effective in stabilizing the behavior of chromosomes during the meiosis in PMCS and accordingly to improve seed fertility of the artificially synthesized rape. As to the number of chromosomes and seed fertility, many aneuploids were revealed in the progenies of surely-selfed C0-1. On the other hand, most progenies crossed with commercial varieties were cytologically stabilized having 2n=38 (Tables 7 & 12). It is considered that occurrence of these aneuploids may be caused by anomalous meiosis in artificially synthesized rapes and also by artificially controlled crossing. With regard to vegetative growth, the progenies of the artificially synthesized rape crossed with the commercial varieties was more vigorous, and had several advantages over the inbred line of C0-1. Therefore, the author considers that the result of this study points out one of the breeding methods in forage rape.

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Variation in the number of chromosomes of autopolyploids in sugar beet (Beta vulgaris) was studied in the established tetraploid lines derived from several European polyploid sugar beet varieties. The exact counting of the chromosomes of polyploid sugar beets is troublesome since complete spreading of all of the chromosomes is difflcult. However, the pretreatment of O. 002 mol 8-hydroxyquinolin for 15 -20 hours at 3-5°C results in extensive shortening of each chromosome and sufficient spreading at metaphase. The materials are very young leaves fixed in NEWCOMER'S fixative, glacial acetic acid, and hydrochloric acid (69 ml. HCI+31ml. water) in the ratio of 12 : 5 : 2. This method promised correct counting of the chromosomes of polyploid sugar beets(Fig. l). Within the maternal lines of the progeny under random mating among the several tetraploid individuals, which were derived from each of the six European polyploid sugar beet varieties, there were variations in the number of chromosomes as shown in Table 1. Without exception, the lines contained some aneu-tetraploids such as 4x±1 (2n= 35 and 37), 4x±2 (2n=34 and 38) and 4x-3 (2n =33). The proportions of aneu-tetraploid in the lines varied with a range of 2. 5 to 62. 5 percent. The means of the proportions fcr each of the varieties ranged from 8. I to 36. 5 percent. In the next year, the eu-tetraploids of MA-4 x line segregated aneu-tetraploid of 7. 8 to 15. 2 per-cent (Table 2). These proportions were somewhat similar to those shown by the original eu-tetraploids derived from Maribo Poly A-1 variety (MA). Reciprocal croses were made between eu-and aneu-tetraploids having 35, 37 and 38 chromosomes in MA-4x line. As summarized in Table 3, the propor-tions of aneu-ploid varied from 20. 3 to 70. O percent, and mostly from 20 to 40 percent. The number of chromosomes in aneu-tetraploids were 2n=34, 35, 37, 38 and 39.

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"Sectorial chimera kernel", possessing an endosperm divided sharply into giutinous and non-glutinous parts, as reported in the previous paper (Tsunoda, Fujimura and Wada, 1964 b) was cultivated and the behavior of germination and subsequent growth of the chimera kernel was closely observed, though the number of kernels to be tested was only one. Two pairs of coleoptile and radicule emerged from the germinated embryos of thc chimera kernel on the 5 th day after seeding. Subsequently, the primary and secondary foliar leaves developed successively from each plumule. From such behavior, "sectorial chnnera kernel" was recogul ed to be"twin", though the existence of two embryos had not been clearly determined by observation of the kernel before seeding (Fig. 1). The growth of these seedlings was inferior to that of normal seeds, and they withered on the 23 rd or 30 th day after seeding. This was mainly due to a decline in the absorption of water and nutrition caused by the very poor growth of the root system. From the fact that "sectonal chimera kernel" was also "twin" the hypothesis mentioned below is a likely explanation for its occurrence. On the supposition that the plant inducing the chimera kernel is heterozygous (Gl. gl) in gene constitution and self-pollinated, the follow-ing abnormal double- fertilization may be considered (Table 1). On fertilizing, two pollen-tubes enter the embryosac, one discharges the gametes partici-pating in the normal double-fertilization and the other discharges the gametes uniting with the synergid and antipodal cell. In addition to the abnormal phenomena mentioned above, if such gene combination occurs as shown in Table 1, consequently two starch tissues differing in chemical composition may differentiate and develop even in the same endosperm. According to the abovementioned hypothesis, two individuals developing from the twin would be gl.gl and Gl.gl in gene constitution respectively, but the withering of plants in the midst of cultivation made it impossible to verify this presumption.

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The mutagenic effects of six chemical cornpounds, ethyleneimine (EI), ethyleneoxide (EO), diethylsulfate (DS), methyl methanesulphonate (MMS), ethyl methanesulphonate (EMS), and propyl methanesulphonate(PMS), were studied in rice. Dry seeds of the rice variety "Gimbozu" were treated with solutions of these chemicals at various concentrations (0.01-1%), or with X-rays (5-50kr) for comparison. In the treated generation(X₁), the chemical agents reduced both the germination rate and the survival rate (lOOXno. of surviving plants/no. of seeds sown) and also delayed the speed of germination, whereas X-rays had no apparent effect on the germination behavior even at the high doses when no plants survived (Fig. 1). The chemical agents as well as X-rays induced chimerical sterility. The fertility of the X₁ plants linearly decreased as the dosage of each agent was increased (Fig. 2). Chlorophyll mutations were induced by all of the chemical agents except MMS. Within the limit of the dosage used in the present experiment, the maximum rates of chlorophyll mutation, 33. 3% per X₁-panicle progeny and 4. 83% per X₂ Seedlings respectively, were obtained at about the LD₅0- dosage of EI. Although the most effective dosages for the other chemical agents could not be determined, the mutagenic effccts of EMS and PMS seemed to surpass those of X-rays. (Table 3, Fig. 4) These results suggest that a higher mutation rate may be obtained from a more proper application of the chemical agents and that at least EI, EMS and PMS are more effective mutagens than X-rays in rice.

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The relative contribution of the various characters to the visual selection made by the 5 rice breeders were evaluated by the method of path coefficient analysis (WRIGHT, 1921, 1960). The 50 lines of F₆ and F₇, one line being chosen at random from each generation of the 25 rice varietal crosses, were planted in a random pattern with 2 replications. Ten characters, measured on a plot basis, were considered ; grain yield, total weight, culm lenght, panicle length, number of panicles, number of grains per panicle, fertility, 500 grains weight, heading date, and lodging resistance. On the other hand, the lines of each plot were scored from 1 to 10 (10 being the best) in the field observations made at maturity by the 5 rice breeders. Then correlation coefflcients between these scores and the various characters were computed. In general, the scores were significantly correlated with fertility, lodging resistance, grain yield, 500 grains weight, and heading date. Other correlation coefiicients were low and inconsistent. Furthermore, path coefficient analysis of the various characters influencing the score were conducted as a means of analyzing the correlation coefficients into direct and indirect components. As the results, more than half of the effects were accounted for in the path coefficient analysis of the 10 characters considered, of which grain yield, lodging resistance, and fertility had strong influences on the score, while 500 grains weight, heading date, and the other characters were relatively unimportant. Therefore, the positive correlations between either 500 grains weight or heading date and the scores seemed to be largely an indirect effect caused by the 'association of the components. Although individual evaluators were affected somewhat differentially, the high correlations were recognized among the 5 breeders for the score.

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F₁ hybrids between a strain of Oryza punctata and three other strains befonging to different species were observed cytologically. It was found that O.punctata and O. malabarensis might have the same BBCC genomes as . O minuta, though these species could be differentiated by translocations.

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