A comparative study on anther ontogeny in male fertile, genic, cytoplasmic and chemically induced male sterile plants of Allium cepa. Beta vulgaris, Capsicum alenuum, Cucurbita Inaxima, Datura alba, Raleunculus muricatus, Sesamum indiculee. Solaleum melongell;a and Triticune aestivum was undertaken. Endothecium in most anthers of MS plants failed to produce fibrous bands and tapetum exhibited abnormalities of various types. The vascular differentiation in the anther connetive was inhibited. The parenchyma cells in this region showed signs of degene-ration and in some MS plants, these cells contained hyaline granules of various types. It is concluded on the basis of the present observations that anomolies in tapetal behaviour in MS plants are the result of vascular deficiency. Presence of intracellular granules in the anther connective may either be due to deposition of substances left unutilized during pollen development or is a result of vascular depletion. These findings also supported the conclusion derived from the histochemical observations by the authors (CHAUHAN and KINOSHITA 1979) .

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A barley mutant resistant to barley yellow mosaic virus (BYMV) was selected from a total of 150 early mutants induced from a variety Chikurin lbaraki I with physical and chemical mutagens. The original variety is a six-rowed covered form with winter habit. The mutant, coded as Ea 52, was originally screened as an early mutant from M₃ after acute irradiation of growing plants at vegetative stage with 250R of gamma-rays. When grown in a field severely infested with BYMV, all early mutants except Ea 52 showed mpre or less leaf yellowing characteristic to BYMV disease and proved to be highly susceptible, while Ea 52 exhibited no such external symptoms. The mutant Ea 52 was crossed as male parent to a susceptible mutant Ea 17 that has a similar degree of earliness. Segregation of resistance and susceptibility to disease in F₂ was clear-cut from the absence or presence of leaf yellowing and stunting. The number of resistant and susceptible plants was 44 and 126 respectively, giving a good fit to the Mendelian ratio of I : 3 that is expected from a single gene inheritance. The resistant character was completely recessive to the susceptible. No sign of association of the disease resistance with heading time was observed. Although diseased plants more or less reco-vered their growth as temperature rose ih April, almost all of them produced lower number of tillers, smaller plant weight and lower culm length at maturity.

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In order to study heterosis of maize, comparisons were made for morphological and physiological characters of germinating kernels between parental inbreds, Oh545. W22 and their F₁ (Oh545XW22) . Protrusion of the coleorhizas and radicles, and the subse-quent seedling growth of F₁ kernels occurred at faster rate than the parents without any difference in imbibition rate of kernels. Hybrid embryo contained more nonreducing and reducing sugar than the parents after 48 hrs of germination. Cycloheximide (5XI0^-5M), an inhibitor of protein synthesis in eukaryotic cell, completely prevented the germination in all the lines with the decline of the contents of nonreducing sugar in embryo at early germination. That the leakage of sugar from kernels to the medium was not detected, would imply that the treatrnent of kernels with cycloheximide was indifferent to the degradation of nonreducing sugar regularly occurring within kernels. During germination, hybrid seedling contained higher amount of RNA than the parents on an individual basis. Soluble protein in F₁ Seedling exceeded parents af, ter 24 hrs. The main protein band detected at cathode side by a electrophoresis decreased faster in F₁ than the parents, and this decrease was prevented by the cycloheximide application in all the lines examined. Thus, it is likely that there is some relationship between the degradation of the main protein band and the germination process.

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The reciprocal crosses were made between two Japanese representative lris species, I. elesata (2n=24) and I. Iaevigata (2n=32), which are highly devoid of afiinity each other, and the development of seeds was embryologically traced from 3 to 33 days after pollination to elucidate the cause of seed failure in process of development. Owing to the seed failure, no viable seed was obtained in either of the reciprocal crosses. In both crosses, the initial symptorn of the seed failure was the start of degeneration of endosperms, which appeared around 21 and 27 days after pollination in I. ensataXI. Iaevigata and I. IaevigataXI. elesata, respe. ctively. The degeneration of endosperm always occurred prior to that of embryos and was not accompanied with any abnormality in such maternal tissues as nucellus and integument. Moreover, it was substantiated by the success of embryo culture in I, IaevigataXI. ensata that embryos could develop normally when put on a suitable medium in place of abnormal endosperm. These findings drew a conclusion that the decisive cause for seed failure appearing in these reciprocal crosses is the degeneration of endosperm.

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To eliminate the usual plant bed costs and to mechanize planting, sweet potato varie-ties adapted to true seed planting (direct sowing of true seeds) is expected to produce. Thus the recurrent selection procedure was applied using natural flowering population, and. the appropriate breeding procedure for developing synthetic varieties was discussed in this paper. In experiment I, flowering habits of natural flowering population were observed under stick-training culture in which two vines per plant were trained along the supporting sticks picking the leaf axils, and also yielding treLits such as number of roots, root weight, root size and dry matter percentage were recorded under the ordinary trans planting culture. In experiment II, yielding traits of the strains selected for number of seeds in the open-pollination of experiment I were evaluated under the true seed planting culture and the strains with high root weight and high dry matter percentage were selected to make a first cycle synthetic variety. Moreover the individuals were selected from the polycross progeny of the selected strains to make the second cycle open-pollinated population.

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One of serious barriers to the breeding of lris plants is the poor rate of seed germina-tion. Aiming at analyzing this difficulty of germination and detecting an effective method to improve the germination, the present study was conducted using the mature seeds of an lris, Iris pseudacorus L. The material seeds were subjected to five sorts of experiments. In two of them, intact seeds were germinated under several different external conditions. In the other three, the testa (and partly also the inner seed coat) of seeds was removed, then the peeled seeds were treated (washed) with cleanser or xylen, and/or partially excised at endosperm prior to germination test. The effects of treatment were estimated by germination rates from 5 to 45 days aLter sowing. The results obtained are as follows: 1. Any external factors did not significantly affect the germination of intact seeds. 2. Removing of the testa resulted in apparent promotion of germination, but the highest possible germination rate was about 20%-3. The germination of the peeled seeds was strikingly promoted by treatment with cleanser, attaining a maximum rate of about 60%· Partial ecising of endosperm also showed the same degree of effect as the treatment with cleanser. 4. The effect of treatment with xylen showed the same degree as the treatrrLent with cleanser. The most powerful treatment was 6 minutes-washing by xylen, which brought about the germination rate over 80-5. No germination inhibitors were detected in xylen extracts from the surface of the peeled seeds.

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Intergeneric crosses between Japanese pear (Pyrus serotina Rehd. var. culta Rehd.) and apple (Malus pumila Mill. var. domestica Schneid.) were carried out in 1974, 1976 and 1977 in order to obtain the basic information for intergeneric hybridization. In 1974, Five pears and three apple cultivars were crossed reciprocally. Out of 1306 pear flowers crossed with apple pollen, 221 fruits were obtained, and 4 fruits in them were seedless. The fruits with seeds gave 1172 fertile seeds. The rate of the fruit set was 16. 9 percent .and the average seed number per fruit with seeds was 5. 4. The fruit set and the seed fertility in the intergeneric hybridization were remarkably lower than those in intervarietal crosses between pear cultivars. From 1152 apple flowers pollinated with pear pollen, 118 mature-fruits were obtained and 4 fruits in them were seedless. The rate of fruit set was 10. 2 percent. From the fruits with seeds, 362 seeds were obtained and the average seed number being 3. 2.

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Effects of radiation on the development of embryos, endosperms and ovules in Brassica ole-racea var capitata were investigated quantitatively in relation to sizes of embryo, cell number of embryo, number of endosperm nuclei, mean cell size and difference between characters of embryo and endosperm. Embryos at different embryonic stages (proembryos and small globular embryos) were irradiated with 10 and 20 KR of gamma rays for one day. For the observation of embryonic tissues, pods were taken for samples at the day of irradiation or 6, 9, 12 and 15 days after irradiation (Fig. 1). Transverse and longitudinal diameter of embryos and ovules, cell number of embryos and number of endosperm nuclei (apical and basal endosperm nuclei) were measured. A central site of continuous paraffin sections was used for measuring the parts of each tissue. In the embryos irradiated at 10 days after pollination, the size of embryos expressed by transverse and longitudinal diameter of embryos was subjected to damages more than that of embryos irradiated at 5 days after pollination (Table 6). Both the reductions of cell number of embryo and number of endosperm nuclei induced by radiation were large in irradiation stages (Fig. 5 and 6). Diameters of ovules influenced by irradiation were so small that their damages were not larger than those of the embryos and endosperm. The cell slze of embryos m 10 and 20 KR exposures mcreased about O.9-3.3 times that of control (Fig. 4). The cell proliferation appeared to be observed in cell of embryos because cell size of embryos irradiated was larger than that of control. From the result of irradiation experiments on embryos, endosperm and ovules, it was con-cluded that the embryo was the most sensitive to radiation damages, followed by endosperm and ovules.

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