Field infection of 15 demissulee-hydrids and progeny of 48005-3 x Voran has heen observed In parallel with artificial inoculation test with common strain of Phytophthora ilefestans in 1954. Among 15 deinissum-hybrids, four seedling varieties, viz. 529-1, 48005-46, 48005-59 and 48005-83 were found to have lower resistance to P. infesta, es through the artificial inoculation on leaves with common strain H₁ These seedling varieties with the exception of 529-1 gave varying degrees of field infection and it has been observed that the infection was due to the appearance of new pathogenic strain H₂. As to the seedlings of 48005-3XVoran the same result was obtained ; those resistant to strain Hi became spontaneously iufected by late August, showing. quite various degrees of infection. The variation in the degree of field infection may be partly due to the so called partial resistance and since little is known on the nature of partial resistance further study will be required in order to clarify the problem of endless host-parasite competition.

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This experiment was carried out in order to ascertain the after-effect of temperature and daylength treatment, given during the seed-ripening period of soybean, on the plant growth and yield in the following generation and also to clarify its ecological significance. It was carried out on the Kanto-Tosan Agricultural Experiment Station, Ministry of Agriculture and Forestry. The seeds exposed to the different temperature and day-length treatrr]ent during their ripening period were sown in 1953. The results obtained may be summarized as follows : 1. Seeds obtained from the different treatments were q'u:ite different in size and weight. In experiment of series X, seeds to be sown were selected for seed weight so as seeds of almost same weight were used throughout all the plots, iri. order to eliminate the effect of different weight of seeds. In series Y on the other hand seeds of representatlve (mean) weight of each plots were used respectively.

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1. The karyotypes of tri-and tetraploid forms were determined as follows : Narcissus ilecomparabilis MILL. "Sir Watkin"

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1. According to the previous report(HAYASE and HIRAIZUMI 1955), the optimum sucrose concentration of artificial, media for pollen germination and growth varies with the age of pollen. In this report the authors attempted to investigate the relationship between the osmotic pressure of different parts of pistil and the age of pistil. 2. The osmotic pressure of the conducting tissue juice of the styles increased during the period from the morning the day before anthesis to the morning of the flowering day, while the ovary juice decreased during the same period. Therefore the difference of osmotic pressure between the style and ovary became gradually greater during that period (Table 1). 3. The refractometer reading of different parts of pistil varied with the age of pistil. The (refractometer)reading of stigma- and style-juice rise with the maturation, while that of ovary juice declined. This was similiar to the changes of osmotic pressure among the diff6rent parts of pistil during the same period (Table 2).

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1. A study was carried out on the development of intersexual flowers and their location on the stalk of spinach. 2. In normal plants, the distinction between female and male flowers is found from the time of differentiation of calyx and carpel. That is, the carpel of female flower occurrs in a convex shape and the male origin develops in a hollowed one, each pursuing an independent development afterwards (Fig.1). 3. From the histological observatio'n of intersexual flowers, three types were identilfied (Fig. 2). That is, (1) the pistil and the starnen stand abreast with each other or (2) Iie one upon the other. And in the other case, (3) the stamen tissue develops in the pistil tissue. Ger!.erally the male flower develops better than the female one.

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In this experiment the authors tried to syntheSize 6x-amphidiploids by the artificial hybridization between Triticulle Timopheevi ZHUK. and Triticum monococcu.m L. in order to combine the leaf-rust resistant genes possessed separately by these two species into a single one, with an idea to make this new wheat to be the good source of resistance to leaf-rust in wheats. By applying 0.05% colchicine solution to the F₁ seeds obtained, 8 mature amphidiploids were grown successfully in adiition to one aneuploid plant (2n = 41 ) . In the root-tip cells of F₁ plants, 21 somatic chromcsomes were confirmed, which correspond to the sum of reduced numbers of their parents, and in those of amphidiploids 42 chromosomes were clearly counted corresponding to the multiple number of chromosomes of F₁ plants. The chromosome configurations and their frequencies at MI of PMCS of Fls and amphidiploids were given in table 2. According to it, the mode of configurations in Fls exists in 611+91, and that of amphidiploids in 2W'+1711, respectively, but there were frequently observed the multivalent chromosomes in both Fls and amphidiploids, which resulted in the fcrmation of variable configurations.

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In the previous report the author (1954) observed the chromosome behavior during meiosis in Meletha rotuudifolia(L.) HUDS. a species possessing the least chromosome number(2n=24)in the genus Me, etha, and described that the above mentioned species is tetraploid consisted of four genomes and very close affinity exists between these genomes. I, n the present report thLe author studied the chromosome behavior during meiosis in one variety of M. viridis L. subsp. crispata BRIQ. usually known as spearmint, which has twofold chromosome number (2n=48) in comparison with the above-mentioned species, ancl the re3ults obtained may be summerized as follows :

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The buds and young leaves of tea are severely damaged sometimes in spring when night temperatures falls several degrees below freezing point. So it is desired to select the tea varieties resistant to frost damage. An excellent opportunity was obtained in order to have a comparative study on frost resistance of tea varieties on June 5 and 6, 1955 at Kanaya, in Shizuokapref., when somewhat light frost occurred. At this time early flushing varieties were in the third and fourth leaf stage, and late varieties were just commencing to flush. In general, the frost hardiness of tea varieties seerrled to be highly correlated with their date of flush-commencement and also with their water content.

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Numbers and values of the factors affecting the combining ability and its heritabilities were estimated with the help the test-crosses which had inbred lines, single cross and back crosses as male parent, in corn. when the test-crosses (shown in the first column of Table 2.) were planted in-plots containing n plants with r replicates, mathematical model of j-th individual in i-th plot is presented in equation (1), and expected values of mean squares within and between plots are shown in Table 2. If heritability of combining ability is defined as following equation ; Heritability

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1. The hybrid sterility between distant varieties of cult{vated rice can be explained by assurning differences in duplicate genes which work in the gamete as; development maintainers, i. e. Gametic Development genes. Segregafion of semisterile and fertile plants due to the G. D. genes is seen when two related varieties A and B, differing in fertility in the hybrids with another variety C, are crossed in the manner : (AXB)XC. However, the outcome of sorne of such crosses showed a discontinuous distribution in good pollen percentage, with several frequency peaks at certain points, such as 75%, 60-55%:, 45-40% and so on. In such cases, the mode of distrihution agreed well with that expected under the assurr)ption of five or more sets of G.D. genes between the varieties A and B. 2. Variation in good pollen percentage in the F2 of distant varieties usually appears to be continuous. An exceptional case was found, however, between two rather closely related varieties, where the variation in good pollen percentage appeared to be discontinuous and to have several frequency peaks. The distribution could be explained by assuming five set:s of G. D. genes independent of one another. Considering that differences in several sets of G.D, genes are thus found between vrieties which are not distantly related, it may be inferred that mucb more sets exist between distant varieties and behave like polygenes. Thus, the continuous variations usually seen in the F₂ and later generations may be explained by assuming certain sets of G.D, genes. though other genes modifying fertility may also exist. It is possible that many dominant genes are needed for the development of the gametes, and since those genes were duplicated a long time ago, many sets of G.D. genes have been formed due to recessive changes in different loci. 3. As an approach to the biometrical genetical analysis, the variation in fertillty in hybrids was calculated theoretically. It was pointed out that the sterility due to G. D. genes vanishes rapidy with inbreeding generations and disappears almost entirely by F₄.

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In previous papers we have already discussed about (1) the development by tetraploids and (2) the development by direct selection. But in this one we are going to described about (3) the development by hybridization. Hybridizations were made between the varieries (A) Tokado and Daruma, (B) Daruma and Beikan and also by (C) three-way-crossing, and we have got two new Fusariulee-wilt resistant varieties developed from (B) and (C). Materials and Methods Varieties. (1) Daruma (D) : An excellent commercial fiber-using variety. This was considered previously as susceptible, because the population of this variety, used as parents of these hybrids, was nighly susceptible to the wilt. Later, some resistant lines weredeveloped from the progenies of this population as shown in report 2. (II) Tokado (T) : A Formosan edible variety of poor fiber. This had been considered as a highly resistant variety. In our recent research, it was infected by inoculation in seedling stage. Mature plants also were injured in September by wilt together with nematode rootknot. (III) Beikan (B) : A Formosan edible variety not suitable for fibber-quality as these fibers are too short, thick and at the sametime coa, rse. But it has been considered as a resistant variety. About 70% of the Beikan population, used in the hybridizations, survived under the infected field condition. (IV) Tsurukubi (Tu) : A fiber-using variety having somewhat longer and weaker fiber than Daruma. It has been considered as a perfect susceptible variety. Methods. Methods used in this research were the same as in report 2, except the crossing practice. First, intervarietal crossing was used. Then, seeds were grown by selfing after F₂ generation.

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