It will be admitted that the introduction of cytogenetical knowledge and techniques into the traditional field of presentflower breeding to make the procedure more effective and popular than in the <)rdinary methods based upon dogmatic, empirical or secret workings has been strongly influential. The, author has carried out investigations along this line for several years by means of induction or detection of the artificial and natural polyploids, mutants, etc. and under the light of cytological and genetical investigations.

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( I ) Unvernalized seeds were sown on November and soon after the sowing, the material plants, selected from the variety groups which differed from each other by ecological characteristics such as spring and winter habit of growth and photoperiodic response after vernalization, were treated for 50 days with differerit temperatures and photoperiods, Then all the materials transfered to the green house with 24 hour photoperiod and their heading behavior was recorded.

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The mutant strain called in this paper " Ieafy head" was found among the third generation lines of an Indica variety "Liew-chew" treated with X-rays. The mutant plants tended to be dwarf, and had a larger number of internodes per stem, shorter internodes, smaller number of tillers and shorter leaves than the normal ones. They produced at the top of the stems many branches with small leaves, simultaneously with the heading of normal plants ; the clump of leaves thus corresponds to a panicle. . The original plant of this mutant appeared in an X₃ Iine consisting of 36 plants. Of the 36, 27 were normal and 9 were the mutant, giving a gbod fitness to the 3 : 1 ratio. However, observing the segrega-tion ratio foir two generations using the offspring of normal plants, deviations from the 3 : 1 ratio due to a reduction of mutants were found in many lines. The normal plants in those lines had a high fertility. From anatomical observations of panicle primordia, the course of development of the leafy heads was divided into four stages, preliminary, first, second and third. At the preliminary stage, the growing point changes to a shoot apex, while some difference from that of normal plants is found as soon as the boot leaf primordium develops ; the number of shoot primordia, possibly corresponding to bract leaves. is larger than that in normal plants. In the first stage, two to three branches develop in the same manner as the differentiation of first rachis primordia in normal plants. In the second stage, many leaf, buds develop from the branches, and in the third stage, several shoots are produced again at the top of the branches. No flower primordia are fcrmed. The leafy heads continually grow under the natural environments of Taichung. However, after a shortday treatment (10 hours), the plants developed normal panicles. It may be assumed that the mutant has a recessive gene whose dominant allelomorph is necessary for panicle development, and cannot produce a sufficient amount of some hormone-like substance required for flower initiation, but shortdays may increase the production of the substance.

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In the previous paper, the authors (1960) divided 'the sexual characters in spinach into two categories, "growth and sexual habit ", and announced that some differences in the growth habit make it possible to classify sexuality into three patterns, two are males with XY chromosomes, called the the bracted :male (B ♂ ) with XY^B and the leafy male (L ♂ ) with XY^L, and the third pattern is female (♀) with XX. It was also reported that the bisexual plant with both male and female flowers occurs in the two patterns, other than B♂ . A bisexual intersex from L♂ is named " andromonoeclous " and another int-ersex from♀ named " gynomonoecious ".

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[in Japanese]

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The frequency of induced mutations in cereals has been denoted mostly in terms of 'the number of mutations per 100 X₁-spike strains'. In this case, workers did not consider the number of individuais within one strain. Since a segregation ratio of recessive mutants in a strain was slightly lower than that from the Mendelian expectation, the smallness of the strains produced by the sterile spikes of X₁ plant caused a statistical reduction in the frequency of mutations. This shortcoming has been overcome by the develop-ment of an elaborate statistical technique(GAUL, 1958). However, the estimati, on of frequency of mu-tations by GAUL's method was so complicated that it has been rufed out of general use. Therefore, the author has proposed an easier procedure in this pa-per and applied it to estimate the frequencies of chlorophyll mutations in rice induced by γrays and pile radiations.

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The tendencies of rice breeding and seeds multiplication in Japan are becoming more intentionally and rationally. The genetic stocks of rice, therefore, are demanded to be more uniform from the viewpoint of gene constitution even in regard to the physiological and ecological characters. In any case of supplyingy the seeds to breeders, these demands for above characters could only be secured by maintaining the bulk seeds of uniform under dry and cold conditior*s. With the advances in the techniques of seeds storage and its practical use on the permanent maintenance of genetic stocks of rice, the authors have hitherto been worked, there seems to be of great significant to apply them to improve the systems of maintenance of breeder's seeds and the procedure of rice breeding as well as the maintenance of genetic stocks. The practical procedures of improved systems are shown with special contrast with present bnes as in Figures 1-4.

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