Sex modification was investigated in the cucumber plants differing in sex expression when they had been alternatively grafted. Understocks were petioles of the 16-17 th nodes of main stems, main and side stems. Scions were seedlings immediately after cotyledon expansion and apical parts of main stems. Survival rate in grafting was higher when understocks were main and side stems and when scion were seedlings. Sex modification was not induced when seedlings were used as scions independently of understocks. On the other hand, hermaphrodite flowers were induced in the staminate flower clusters when apical parts of androecious plants were grafted as scions. This might have resulted from the transformation of staminate flower primordia at physiological bisexual stage till completion of grafting union.

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1. An allooctoploid plant (2n=96. BBBBCCCC) was induced through colchicine treatment to the germinated seeds of allotetraploid species. Oryza minuta PRESL. (2n=48, BBCC) . 2. In the octoplod-minuta, anther development is delayed, and the meiosis in PMCs begins only when the top floret of panicle is just coming out of the flag-leaf sheath. The same tendency is observed in octoploid-latifolia. 3. Meiotic chromosome behaviours in PMCs Were studied in detail. In Diakinesis, the number of tetravalent chromosomes formed per PMC ranged from 4 to 13, and the mode, was 9 and 10, the average being 9.14. In MI, the range of tetravalent chromosomes became somewhat wider, the number varying between 3 and 15, the mode and average per PMC being 7 and 7. 26, respectively. Correspondingly, the average number of bivalent chromosomes increased from 29.68 in Diakinesis to 32.60 in MI. Lagging bivalents were observed frequently in MI. Very few trivalent chromosomes werelobserved in Diakinesis and MI. The irregularities became more obvious as the meiotic stages proceed from AI to Pollen Tetrad, producing finally many abortive pollens. Most of such abnormalities seemed to be due to non-orientation of bivalent in MI. On the female side, however, gametes seemed to function rather normally. 4. The seed fertility was extremely low even in open pollination condition. The cross-ability between tetraploid-sativa and octoploid-minuta taking the former species on the female side was lower comparing with that between the undoubled original species. 5. Octoploid-minuta gave gigas-type in most characters as compared with the original tetraploid-minuta, though not so conspicuous as in the case of O. latifolia. The size of stomata, pollen grains and spikelets increased, while the number of panicles and panicle density decreased remarkably. Like tetraploid-milnuta, octoploid-minuta is also very low in the sensitivity to the day-length.

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Crosses between each of the six testers with the marker genes of NAGAO and TAKAHASHI and Somewake having the highest tolerance to cool were made in an attempt to clarify the linkage relations. Each marker character behaves as a single gene to normal. The degree of cool tolerance was evalueted by sterile index (sin^-1√(%)) in the cool water irrigated field. As the results, cool tolerance was associated with the genes d₂ (II), gh (VI), nl (IX) and bc (XI), but not with the genes Rd (III), g and Rc (IV), Ia (VIII) and bl (X) . In addition, it was suggested from the authors' previous paper that cool tolerance was associated with the genes Pr (II) and one of the genes for awning (VI or XI), but not with the genes C (I), A (III) and the othe one of the genes for awning (XIII) . Therefore, the number of pairs of the genes controlling cool tolerance was estimated to be four or more. The reliability of the genetic models postulated was discussed, particularly with reference to the frequency distributions, and it was suggested that the inherent mode of cool tolerance would be considerably complex.

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Resistances to the blast fungus strains in rice variety Pi No. 1, bred by repeatedly crossing a Japanese variety, Senbon Asahi, with a Philippine variety, Tadukan, were genetically analysed. The variety was found to carry a gene Pi-a controlling high resistance to fungus strains, Ina 72 and Ina 168, and another gene Pi-ta controlling semi-resistance to fungus strains, Ina 72, Hoku 1, Ken 54-20, and Ken 54-04. Some lines which carry only gene Pi-ta were selected. Gene, Pi-ta, was found to behaved independently of genes, Pi-ta, Pi-i and probably Pi-k.

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Metntha arvensis L. grows in the temperate regions of the northern hemisphere such as Europe, North America, and Asia (including Japan), and is abundant in variation. Collecting 29 strains belonging to 3 subspecies of M. arvensis from their original habitats and artificially raising 5 F₁'s belonging to 2 intervarietal hybrids, the authors carried out their cytogenetical investigations as part of their fundamental studies of mint breeding. The results were as follows : ( 1 ) M. arvensis var. canadensis is distributed in North America and M. arvensis var. piperascens is distributed in East Asia. Each has 96 chromosomes in the somatic cells. M. arvensis var. agrestis and var. praecox which are distributed in Europe have 72 chromosomes in the somatic cells. The former 2 varieties are octoploid and the latter 2 varieties are hexaploid, considering the basic number of chromosomes of the genus Mentha to be 12. ( 2 ) There seem to be no structural variations of chromosomes between var. canadensis and var. piperascens, because F₁ plants have nearly as high a fertility as that of the parental plants and are complete in the conjugation of chromosomes in meiosis and no univalent chromosomes can be seen. ( 3 ) Artificially raised F₁ hybrids of var. canadensis and var. agrestis have 84 chromosomes in the somatic cells, and 36 bivalent chromosomes and 12 univalents appear at MI in meiosis. The behavior of chromosomes in the meiosis of the F₁ hybrids mentioned above is just the same as that in F₁ plants from var. piperasc, eles and var. agrestis which the authors raised and about which they have already published. So it is clear that var. canadensis and also var. piperasceles must have appeared naturally from hexaploid varieties with 72 chromosomes by the addition of two sets of twelve chromosomes. ( 4 ) A variety of M. arvelesis which was collected in the vicinity of Rock Lake in the U.S.A. have 84 chromosomes in the root-tip cells, and 36 bivalents and 12 univalents at MI in meiosis just as the artiflcially raised F₁ hybrids mentioned above. This variety can be assumed to be a natural heptaploid hybrid between the octoploid variety from the U.S.A. and a hexaploid variety similar to the European mint. A strain of M. arvensis var. agrestis [152-9] is male sterile and its meiotic cell divisions of PMC's cannot be observed. The cause of this abnormality was sought histologically and it was found that the degeneration of archesporial tissue occurred about the time when pollen mother cells differentiated and before their meiotic cell divisions began. A similar phenomenon was observed in four other strains of our collection, so it seems to be a common occurrence in this species of mint.

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A dominant gene Ws(pbg) of Nicotiana plumbaginifolia covers the effect of a recessive allele ws of N. tabacum which conditions an inability of chlorophyll production. As.. additional plumbaginifolia chromosomes are somatically unstable in tabacum nucleus, the hybrid plants are usually mottled. Soaked seeds of a hybrid derivative plant of which chromosome constitution was 24. pairs of tabacum chtomosomes (ws ws) plus one plumbaginifolia chromosome ( Ws(pbg)) were irradiated by 5.000 R of X-ray. Self green sectors and leaves were observed insome mottled X₁ plants. Some of the X₁ plants were branched and self green leaves, were developed on one of the branches. Meiotic configurations of these X₁ plants andsegregation ratio for leaf color in X₂ generation proved that the self green sectors and leaves were due to interspecific translocations of Ws(pbg) . It was observed that an inflorescence of some X₁ plant was genetically heterogeneous. The transmissipn rateof Wg(pbg) translocated to tadacum chromosome rec. iprocally was very low. The rate of the induced translocation of Ws(pbg) was about 5%.

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The effect of embryo transplantation on crossability between wheat (Triticum aestivum) and rye (Secale cereale) was tested. In this experiment, 6 wheat varieties and I wheat-rye strain were used. As regards their crossability with rye, 4 wheat varieties (Nisimura-kawari “mutant-Nisimura ”, Konosu No. 25, Honkei No. 124 and Fultz) were poor 2 wheat varieties (Nisimura and Norin No. 29 and the 1 wheat-rye “(Nisimura X rye) F₈-26” were strong. The rye variety used was Petokuser. Embryos and endosperms were separated after water absorption for 17-20 hours. The assortment of embryos and endosperms (embryo/endosperm) was as follows : (1) wheat/rye x rye, (2) wheat/rye with cut endosperm x rye, (3) wheat/wheat x rye, (4) wheat/-* x rye (5) wheat x rye/wheat and (6) wheat/-* x rye/wheat. (* shows the separated wheat embryo without transplation on the endosperm.) The effect of endosperm was quite small or non-existent.

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Edgeworthia Gardineri from Nepal Himalaya is studied in relation to its use as a possible source of paper materials. The study was done in comparison with the Japanese corresponding species, E. papyrifera. The Himalayan species has the chromosome number of 108 at root-tip cells so it is 12X, because the basic chromosome number of Edgeworthia is X=9. The general morphological characteristics of the Himalayan species are almost similar to the Japanese species which is usually tetraploid, but the former has larger and thicker leaves and is evergreen while the Japanese species is deciduous. When the Himalayan species is compared with the artificially induced Japanese octoploid plants, it has. larger stomata cells, more chloroplasts in them and longer hairs on the leaves, but shorter fibre cells in the bark which are most important for paper materials.

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“Shititoui”, Cyperus tegetiformis Roxb. (C. malacelesis Lam.), propagates by underground stems and cannot propagate by seeds, but “Wangul” (Cyperus lwasakii M. and C. glomeratus L.) propagates very well by seeds. So, the minimum temperature of seed germination of Wangul is one of the important characteristics to consider seriously in cultivation. In order to know the minimum temperature of Wangul, germination tests were carried out in 1941-43, at the South Branch of the Chosen Government Agri. Exp. St., using such eight varieties such as Pukchon (S. Hamgyeng pref. of North Korea) . Kanghwa (Kyengkwi pref. of Middle Korea) and Uisong (N. Kyengsang pref. of South Korea) differing in harvest period (early or late) and in the form of the stem. By using weighing bottles with a diameter of 3cm and height of 5cm containing 4cm deep river sand and 3.5cm of deep water, the experiment was carried out in a thermostat at 30°C, considered to be the optimum temperature, and at 10-18°C. Examination of the number of sprouting seeds was carried out at 10a. m. every day. The last germination test was on the 14th day. The result obtained was that the minimum temperature for seed germination of “Wangul” is 13`15°C.

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