Considering the present results, a hypothetical scheme was set up as shown in Fig. 6 which may explain the developmental mechanism of the induced mutation in the R₁-plant. In the scheme, the circles in which tiller numbers are marked mean the corpus cell groups leading to the fcrmation of the generative tissues of the numbered tillers, in the shoot apex of the irradiated embryo.

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Summary In the previous paper (Yamagata and Syakudo 1960), it was reported that various aberrant plants were induced in the X2 generation following T-irradiation of seeds of two rice varieties, Gimbozu and Aikoku, and two strains derived from their cross. It was considered, however, that some of the aber-rant plants might have been due to environmental effects and not real mutants, and conversely some normally appearing plants might have been mutants, because the quantitative characters we exami-ned are usually affected by both genotypes and environments. In order to clarify this point, the progenies of a considerable number of aberrant and normally appearing X₂ plants were grown as sepa-rate lines in the next generation. The progeny tests were made for several quantitative and qual-itative characters separately. The results obtained are as follows : ( I ) Some of the normally appearing plants in the X₂ generation segregated a various proportion of mutants in the next generation and the progenies of some aberrant plants were normal. However, the proportion of mutants was significantly higher in the prognies of aberrants than in those of nor-mals (see table 2). ( 2 ) Although a significant correlation was found between X₂ plants and their progenies in quantitative characters such as heading date, the prediction of progeny phenotypes from X₂ plants is very difflcult, because some extreme X₂ plants in one direction can segregate a proportion of extreme' phenotypes in the other direction (see fig. 2). ( 3 ) In the X₃ generation various mutants were found which had not been observed in the X₂ generation with respect to type or degree of varia-tion. Further, a number of promising mutants such as early maturing, stiff culm, many-grained spike, etc. were observed. Numerous genes seem to be concerned with these mutations, and some of them possibly have a pleiotropic effect on several characters. However, most of the easily detectable mutations such as chlorophyll deficiency, coloring of apiculus, emergence of awn, etc. appeared to be independent from other quantitative mutations. ( 4 ) The results mentioned above suggest that-fcr the selection of mutants the progenies of normally appearing X₂ plants as well as aberrants should, be examined in the next generation. As to heading date, the relatively late heading plants in the normal type of the X₂ generation segregate a larger proportion of mutants in the next generation than those of relatively early heading date. 20

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In order to determine whether the hard seed con-tent of Renge (Astragalus sinicus L.) is heritable or not, about one hundred inbred lines were examined in regard to this character. Results obtained are summarized as follows : ( I ) The hard seed content varied considerably with the inbred lines and the line means ranged The 'continuously from 2.I to 59.5 per cent. The analyses of these data showed that differences among lines were statistically significant. Heritability estimates were O.8-0.9 on line means and O.6-0.7 on individuals, and the correlation coefflcient between the parents and the progenies was +0.42. Tn' ese results show that the hard seed content is influenced by environmental factors but simultaneously depends on genetical ones. ( 2 ) Correlation coefficients between the hard seed content and some other ch.aracters such as length, thickness and color of seed were all small and not significant. But a significantly higyh correlation was found between the hard seed content and the seed weight. 24

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1. An investigation was made on the interaction between genotype and planting density in rice -plant, with the aim of contributing to the breeding of varieties adapted to high planting density. 2. The experiment consisted of two different forms of culture, i. e., early season culture and ordinary season culture. In early season culture ten varieties were used which were randomly chosen from the leading varieties in T5hoku District and in ordinary season culture again ten varieties from those in Chilgoku District (Okayama and Hiroshima Prefectures). The materials were grown under three different planting densities, i, e., 30cmX30cm, 2lcmX2lcm, 15cmX15cm, in a split plot design of 3 replications. The characters examined were culm length, panicle length, number of panicles, panicle weight per plant (yield), panicle weight per stem and heading date. 3. Mean values of the characters investigated decreased, as planting density increased, except culm length in. ordinary season culture which, on the contrary, increased. The effect of planting, density on the mean values was not the same fcr early and ordinary season cultures, varying with character. Analysis of variance indicated a significant interaction between genotype and planting, density in several characters such as yield and number of panicles. 4. The heritability estimates of various characters generally decreased as planting density increased, except that of culm length which showed an increasing tendency. 5. Since the heritability was generally higher in low plahting density than in high planting density, the genetic gain in high planting density from the selection in low density was examined, using the following formula (Falconer, 1960) (CRY)/(RY)=rA(i_x)/(i_Y)(h_X)/(h_Y) This examination showed that the selection for number of panicles is more effective when conducted in low density than in high density. In other characters, however, the indirect selection was cosidered not necessarily advantageous to the direct selection in high density, taking into account other facters such as sampling error and natural selection in breeding processes. 6. Summing up all the results it was concluded that the best method fcr breeding varieties adapted to high planting density may be F₃ derived line method, or bulk method in which the breeding materials are grown in low planting density until around F₅ in order to minimize the effects of competition and then selection is conducted in high planting density on the basis of line means.

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(1)Eleven strains of mint which have morphological characteristics of Meletha gentilis were represented by the material used in this research. Ten of them were considered to be identifiable with Mentha gentilis L. f. cardiaca(SM. ) BRIQ. by comparing their characteristics with the textual description of this mint species. (2) Karyological figures and morphological characteristics of the material above mentioned were also compared with those of F₁ hybrids (2n=72) between M. arvensis L. var. piperasceles MAL.. (Japanese mint, 2n=96) and M. spicata L. (including var, crispa BENTH.) (2n=48). And it was considered that M. gentilis f. cardiaca must have originated frolorl this crossing, on account of the close resemblance between the two. (table 1 and table 4, fg. I and fig. 6).

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1. For testing thermal and photoperiodic induction during seedling stage, two winter barley varities differing from each other in short day vernalizability, were treated from germination up to 5th leaf stage, under the following three conditions. They were then transferred to high temperature long day condition and heading behavior was recorded. A : cold and short day concurrently (out door-natural day length) B : cold treatment only (out door-24 h) C : short days only (green house-natural day length) 2. Number of days from transfer to heading, decreased with increasing duration of each treat-ment. 3. In case of cold treatment only there was no difference in thermal induction between two varieties but difference occurred between them in case of short day only or cold short day and KOBINKATAGI headed earlier than HASHIRIHADAKA in either case. But the difference of number of days from transfer to heading was reduced when seedlings were treated until 4 th leaf stage, except in short day induction of HASHIRIHADAKA. It is estimated from these results that the induction of winter barley must be enhanced considerably until 4th leaf emerges in the field condition of south west Japan. 4. The comparison of heading behavior between those two conditions, that is, cold-short days and cold-long days suggests the co-existance of thermo-phase and photophase. 5. In the second experiment, effect of order of thermal and photoperiode induction was tested. 6. The effect of the brder of short day or lowtemperature on floral induction of winter barley was not so significant and the difference of heading behavior in the second experiment was explained by the difference of short day vernalizability of the two varieties. The younger the seedlings the more vernalizable they are.

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(1) Paper chrolrLatographic experiments were carried out in order to determine the kind of anthocyanins, and to clarify their genetical behaviours using H. cocciea, H. moschata and F₁, F₂ and F₃ hybrids between its parents. (2) The color of H. coccinea, H. moschata and F₁ hybrids were dark red, exceedingly light red purple and dark red purple. The color of F₂ and F₃ hybrids between its parents were varied between the darkest red purple like F₁ and the lightest color as light red purple excepting such plants as the color of H. moschata. (3) As regards aglycones, the each material used was cyanidin. (4) As regards cyanidin glycoside, H. coccinea and all hybricls used in this experiment were all chrysanthemin (or idaein) and keracyanin, but H. moschata was chrysanthemin (or idaein) and "moschanin", which was newly found and named complex glycoside in this paper. (5) The manifestation of the color pigments of the materials used in this paper seems to be controlled by polygenes and be concerned with many multiple genes.

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