Hybrid population of a lvinter lvheat cross was dealt with in this selection experiment. Norin No.8 is one of the resistant varieties for winter hardiness and the reverse is true for U-13 (TrumbullX Frondosa). Population was divided faur parts. Three parts were exposed to low temperature in mid-wintcr repeatedly in the F₂ (:IV), F₂ and F₃ (V), F₂, F₃ and F₄ (:VI), respectively. In the F₅ generation, each of 1, 000 progenies selccted at random from three parts of population and non-trcated population (III) were planted, and 100 plants werc selected at random in the field. Among them further 50plants were selccted. They showed high percentage of grassiness for grain hardncss. In thc F₆ generation, all these 200 lincs lvcre comparccl with (A) cold resistance, degree of which was evaluated by exposurc treatment to low tempcrature ( -24.5°C), (B) snow blight ( Sclerotinia graminearum ELEN) resistance, and(C)growth habit, erect or prostrate, which was mcasured by angle. 8lines selectcd by pedigree mnethod (I) and two parental varicties (II) were also dealt with. These matcrials were grown by randomized block arrangement with two rcplications. Table 1 shows the origin of materials and the breeding schcme. As can be seen from Fig.1, differences between the populations in the mode and the range of variations were remarkablc. Among the six populations statistically significant difference was found. The range of each population is as follows; (A) cold resistance (strong>weak) : (VI)>(V) >(IV) = (III)>(II) = (I) (B) S.g. resistance (strong>weak) : (V)=(VI) >(IV = (III) (C) growth habit (prostrate>erect) : (II)=(V)= (VI)>(III) = (IV ) Table 2 shows that (V) and (VI) were more resistant or prostrate than (III) and (IV). Furthermore, according to Table 3, in the populations of (V) and (VI) there are many resistantlines as Norin No. 8. Six lines of (VI) populations showed signihcantly high cold resistance than Norin No. 8. The degree of heritabiiity of the three chairacterswas estimated by the analysls of variance (Table 4). Defgree of heritabilities of each character was as followos ; growth habit, 75% ; cold resistance, 67% ; S.g.resistance, 44%, respectively. Difference was found in thc degree of heritability among thc six populations. Bttsed on the data of covariance analysis, genotypic and phenotypic correlations between three characters were estimated (Table 5). Genotypic correlations were, in general, higher than phenotypic correlations. Fairly high neogative corrclations were found between degree of cold injury and growth habit. Moreover, high positive genotypic correlations were found between degree of cold injury and those of S.g. injury. According to the results, it seems likely that selection to growth habit in early generations might be effective for the improvement of populations regarding the cold resistance or S.g. resistance, so far as this kind of combinations is concerned.

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Hybrid population of a wheat cross, Dawson No. 1 XPurcam was grown as a bulk from the F₃ to the F₅ generation with limited phosphate for increasing winter-killing. In the F₃ generation susceptible plants to leaf rust were discarded. 600plants lvere selected at random in the F₅, and 5 grains were taken from each plant. 3000 grains were mixed and divided into three groups. In the F6 each of 1000 grains were sown under the following three conditions. a : Average density for yield triai. b : Two fold of density, comparing c condition. c : Stanclard density of 1{ne growing. Plants with more than 3, 4 and 5 ears were selected under a, b and c conditions in the flcld. Each 100 of lincs selected from the thrce conditions was grown again in cach condition under randomized block atrrangement with two replications in the F₇. Twenty percent of lines with high yield were selected in each condition. In the F₈ 60 lines with parent varieties were grown under randomized block arrangement with 3 erplications. Accordingr to the result of yield trial, it was remarkable that c group included more number of lines with high yield than the other two groups (Tables 1 and 2). Consequently, it was recognized that the selection for high yield in the c condition was fairly effective, comparing those under the more dense conditions. Regressions of F₇ on F₈ and those of F₈ on F₇ were calculated(Table 3). As can be seen from the table, regression coefficient of the line yield of F₇ on the individual yield of F₆ in the c condition was rather high and highly significant. Based on the covariance analysis, phenotypic and gcnetic correlations between yield and number of ears, and between yield and winterhardiness were calculated (Table 4 ), and they were suprisingly high. Connected with these finclings, it was assumed that under c condition genlc expression regarding numbcr of ears, winter hardiness and yield itself was magnilled or exaggerated, and it should play an important role to raise the efrlciency of selection. If phenotypic variance increases parallel to increase of environmental and genctic variance, genetic advance duc to selection will rise. In addition, relations between efficiency of selection and heritability, and, genetic and environmental variances were discussed. It is plausible that plant breeder could find good growing conditions to the selection for characters with low heritability, where the efficiency of selection might be fairly high, according to the magnification of genotypic diffcrences, or accompzlnying full exemplification of the genotypic ability without limitations.

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1. The reciprocal crosses were madc between H. mutabilis and H. Moscheutos as the studies on the hybridization in species and genus crosses in Malvaceae and F₁ seeds and plants Were obtained from H. mutabilisxH. Moscheutos. 2. The set % of pods in H. mutabilis X H. Moscheutos was 35. 26%, but that of pods having the viable seeds was 13. 16%, and the pod fertility, percentage of pods having the viable seeds per total pods, was 37. 31%The size of pods obtained in H, mutabilis X H. Moscheutos was smaller than that of the selfed mother, the shape of F₁ seeds obtained resembled the mother plant, but its size was smaller. which was shrub. 3. The number of the viablc seeds per pod obtained in H. Mutabilis X H. Moscheutos was only 3. 3, but that in pods having the viable seeds was 8.8. The germination % of F₁ sceds was 41.67%, showing the lower value than those of the parents. 4. The shape of cotyledons of F₁ quite resembled the father plant, but its size was smaller. The shape of leaves of F₁ was rather similar to the mother plant rcsembling the intermediate shape bctween the parcnts. The shape of flowers of F₁ quite reselmbled the father plant, but its size was smaller, showing the. intenrrediate size of the plants. The colour of flowers of F₁ was dark pink, but that of the mother plant was white, and of the father plant was light pink. The time of blooming of F₁ in the first year of growth was later than the intermediate time of the parents, but that in the second year of growth was equal to the mothel plant, bloonrling earlier than the father plant. 5. In F₁ the plant height was low showing the similarity to the mother plant at the early stage in the first ycar of growth, but elongated to the height of the father plant in the middle of October, and became at the end taller than those of the parents in the middle of October in the second year of growth. The thickness of stems of F₁ was more than those of thc parents, and the numbers of leaves, nodes and branches were more nurnerous than thowe of the parents. The plant type of F₁ was variou observing 9 types, and no individuals of the same type to the parents were obtained. The tissue of stems of F₁ quite resembled to the mother plant which was shrub. 6. The pollen grains of F₁ were of various sizes and almost all the pollcn grains were abortive, and the pelcentage of good pollen grains was O. 3%. Thet size of good pollen grains of F₁ was larger than those of the parents. The number of pollen grainsper anther of F₁ was more numcrous than those of the parents.

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This investigation was undertaken to see the morphological, physiological and cytological characters of triploid clone of the Japanese mint and also to study its economic values. In 1905 and 1956, 35 triploid clones (3n, somatic number=144:) of the Japanese mint were raised by the crossings of induced tetraploid clones (4n=192) with diploid clones (2n=96). The inverse crossings, however, did not succeed because of the failure of germination of the seeds obtained by crossings. Hence the triploid clone has not yet been obtained by 2nx4n. As the basic number of chromosomes in the genus lklelctho is twelve, strictly mosomes in the genus lklelctho is twelve, strictly speaking the Japanese mint, its triploid and tetraploid clone, should be called octaploid, dodekaploid and hexadekaploid clone, respecfively. However, for convenience' sake, the authors will name them respectively, diploid, triploid and tetraploid clone of the Japanese mint as mentioned above, in this paper. The triploid plants grow well and are somewhat larger than 2n plants in the vegetativc orgnns. Leaves are ovatc-oblong, not so broad as the ovate leaves of 4n plants, but broader than the lanceolate leaves of 2n plants. Guard cells of stomata, hairs and essential oil glands of 3n plants, which are all observed on the epidermis of their leaves, become larger or longer than those of 2n plants, but are not so large or long as those of 4n plants. On the contrary, their numbers in the unit area of leaves are reduced as compared with those in 2n plants, though not so much reduced as those in 4n plants. Flowers come into bloom from July to September in Okayama district. Early clones are as early as 2n ones and late clones are as late as 4n ones. Anthers become atrophied and no fertile pollen is found in the pollensac in any of 3n clones. Seeds set ncither in open pollination nor in back cross to parents. In 1957 about 1800 flowers were tested and only three seeds were obtained. It is presumable that fertility is nearly zero in the female gametic organ as in the male gametic one.

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An X-ray induced mutant of 4-rowed lvinter barley produced awn of diverse types in a spike (Table 1). This was more variable in the intensity of expression than the analogous mutant subcalcaroides described by BANDLOW (1954), as shown in Fig. 1. That is, this mutant makes partly the same structural pattern, but gives different end product of development, as corrupared with subcalcaroides. As the mutant's spikes were divided into three kinds : n-, n→a-and a-types (Table 2), X₃ progenies were classifled as given in Table 3. However, no plant having spikes of n- and a-types was found in X₃-and X₄-generations. Although the seeds were selected from the plant having spikes of each type in X₃ generation, no of Tokyo) change was observed in the appearance of abnormal plants in X₄. (Table 4). The expression of mutated character intensified at the early differentiated part, such as early heading spikes or the upper portion in a spike. Thus. it is probable that the spikelets of lateral row differentiate later in comparison with those of middle row at the same position (Fig. 2). In the cross with mother-type or hooded, the inheritance of mutant character is completely recessive. From these results, it is concluded that the mutant character is induced by point-mutation and its gene-expression is affected by some environmental factors, probably temperature etc

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[in Japanese]

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It was reported preliminarily that the triploid mulberry plant (3n=42) was obtained by crossing the female flower with diploidized egg cell caused by the treatmcnt of 0.2% colchicme aqucous solutron and normal pollens. Out of 190 scecllings survived from O.2% colchrcme treatment only one was found to be triploid in somatrc cells. In the induced triploid leaves the size of stomata was larger and the distribution density of them was lower than its parents.

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