1. In order to clarify the effective selection method of the mutation breeding, this experiment investigated the relation between the order of tiller and the induction of the mutations in the rice varieties 'Towada' and 'Hattukoda' treated with the radioisotope ³²P. 2. Generally, the main stems and each of the lower primary tillers were mutated independently. But, sometimes, these stems when induced to the same type of mutations, they were often sectorial chimeratic on the induction of the mutation. 3. It seemed that the frequencies of the visiblemutations in the lower tillers were comparatively higher than that in the higher ones. 4. The inductions of the mutation in the secon. dary tillers were similar with that in the primary ones from which they grow. 5. Relatively high correlation was found between R₁ spike fertilities and R₂ Iines fertilities, while there. was no difference in R₂ mutation rates by the different fertilities of R₁ spike.

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(, 1) In the case of crossing where plants of the "a" genorne group (Chinese cabbacre varieties) were used as the female parent and those of the "c" genome group (cabbage varieties) as the pollen parent, only seven seeds were harvested from 1998 pods produced through 2, 925 fiower pollinations. These seven seeds wer.e larger than usual Chinese cabbag.e seeds and all produced matroclinous seedlings, however, all the other ovaries ceased their growth in early stages and their embryos degenerated so early that their artificial culture was regarded as impossible with our present embryo culture techniques. (2) In the case of crossing where the F₁ hybrids of B. alboglabra and cabbage, both belonging to the "c" genome group, were used as the female parent and the variety Shimoyama-chitose of Chinese cabbage as the pollen parent, 155 flowers were pollinated and eight young embryos were removed 40 days after pollination. These embryos were cultured in a culture media roodified from WHITE'S basic solution and three hybrid seedlings were grown successfully. Another variety Nozaki No. 2 of Chinese cabbage was used as the pollen parent and 46 hybrid embryos were removed 30 days .after crossing where 250 fiowers were pollinated. Twenty two hybrid seedlings were reared from these embryos. However, from the pods pollinated and left on the female plants six large seeds were harvested, all of which produced matroclinous seedlings.

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Through the methods of S. N. HAZEL (1943), I made the selection index of F₂ poputation on three characters, Iength of cocoon filament (m. X₁), weight of cocoon filament ( cg, X₂) and width of cocoon (1/10mm, X₃), of silkworms. Also I, calculated heritabilities and genic correlation by the way. Heritabilites and genic correlations were gained by means of F₂ population and back-cros;s populations and their values are given in table 3. The selection index with three characters represented by units in brackets will be given as f emale I = 22X₁ + 852X₂ + 42X₃ male I = 66X₁ - 854X₂ - 154X₃ if breeding purpose is H=G₁+G₂ where X₂ is a phenotypic value. G₁ is a additive genic value and H is the genic value of their composite characters. In the real case, I think that we can carry F₂ to F₃ by random mating, after excluding inferior in dividuals of F₂ population by these indexes. Besides, these three characters are not meaningful particularly, and what is breeding purpose, is another pr.oblem.

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The writer (1958) has reported that the seedlings of S, semp obtained from seeds produced in California have the high hybrid population and this strain may be considered as an apporopriate material for purposes of the selection. The present paper is dealt with the statistical analysis on the characters of the branch of trees belonging to the above strain. Twelve individuals of 3-4 year old seedlings were examined. This material group showed the high variability coefiicient similar to those of the previous paper. There was the significant difference at I or 5 % level between the characters of each tree. The distance between the successive branches on the stem varied with the branch position on the stem, while there was any regular correlation between the distance and the branch position on the stem. Therefore, method expressing the number of the branch on the stem may be worthy of consideration. An angle of the branch at the upper position of a crown, near the center, and at the lower one was an acuter, an average value, and a blunter, respectively. However, its deviation could be ignored. The number of sub-branches varied with the parts of insertion of branch and no correlation was detected between the both. Positive correlation coeffilcient at the l%-level significance was recognized between the number of sub-branches and the length of the branch; and between the diarneter and the length of the branch. In the height of tree and the diameter of a crown the high positive correlation was seen between the total increment during 3 years from 1951 to 1953 and during 4 years from 1951 to 190r4. The correlation coefiicient between the total inctement of the tree height, the crown diameter, and the stem diameter at 10 cm above ground and some characters of the branch is given in the table 6. In the preceding paper the after effect of seed activity was described, in which, there was no significant correlation coefficient between the total increment of tree height, the crown diameter, and the stem diameter during 3 years (1951 to 1953) and the increment of such characters during 1 year in 1954. On this hybrid population, the size of the sample required for the expected standard deviation concerning the each character was measured. In the present paper the writer discussed the method of measuring some of the characters giving the peculiarity of these characters and the size of the sample consideration.

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Young shoots of sweet potato plants were irradiated by X-rays to induce some new "sports" due to somatic mutations. As sweet potato plants are usually propagated by vegetative reproduction, that is, by planting young shoots from parent tubers, the X-radiation of young shoots was considered asthe effective treatment method to induce artificial mutations. We irradiated the young shoots sprouted from tubers of variety Norin No. 1, which produce tubers of brown red colour, at the dosage of X- rays ranged from 5000 r to 20000 r and 61 r/m in intensities at all cases. After treatments, shoots were cut to some short pieces having one leaf on each and planted in little pots of 10 cm diameter. Although some irradiated shoots died, almost ones were sprouted after fewweeks. Survival rate was decreased linearly according to the dosage and 30 per cent of shoots treated by 20000 r survived at maturity. Many varia. tions of leaves, stems and tubers or inhibitions of growth were recongnized in the treated generation and such variations in X₁ was seen as to increase with the treated dosage. Main variation was recorded on frequent appearance of chimera tubers with epidermis colour of brown red and yellow white.

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In this paper the writer deals with the location of flowers on the stalk and flowering habit in buckwheat. Especially seasonal difference between summer and autumn strains regarding flowering habit is ascertained. 1. The flower of buckwheat is formed at the lower part of stem and spreads to the upper part. In comparison to several characters, the leaf which has flowers becomes slender and longer (Tab. 1) than that on other part, and the internode is also shorter. This tendency of internode is accelerated in auturnn sowings and retarded in summer(Tab. 2). The flolver cluster forms secondarily on the branch and some difference occurs in the situation of branches (Fig. 1). The generally-called flower cluster is divided here into ten or more minor flower clusters (Fig. 2). 2. The order of flowering of the flower cluster seems to behave independently from each others. This order in a stocl.c is controlled by the location of fiowers (Tab.3). A daily investigation of flowering brought a true feature of it (Tab.4). 3. 80% or more of flowers bloom from 6 to 8a. m. The flowers, do not bloom other in the afternoon or at night. But delay in flowering is caused by lower temperature (Tab. 5). 4. The flowering is quicker in summer strains than in autumn ones. Moreover the speed is lowered when sown in May, but is elevated when sown in September (Figs. 3-4). The speed can also be compared morphologically by the degree of growth in flower cluster (Tab. 6).

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[in Japanese]

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[in Japanese]

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[in Japanese]

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[in Japanese]

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