Length of dormant period in Avena species was determined by germination of seeds harvested during the period from June 11 to July 9. Test samples were collected from four diploid species and one induced autoteraploid (4 x), two tetraploid species (four varieties) and one induced autotetraploid (8 x), and four hexaploid species (eleven varieties) at a ripe stage.

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1. Relationship between the water content of dormant seeds of several plants and their sensitivity to X-rays and γ-rays was studied. 2. Sensitivity of dormant seeds to various radiations was at a minimum when they contained from about 12 to 18% water, except for rape seeds. 3. Resistance of dormant rape seeds to T-rays was at a maximum when they contained from 5 to 8 % water. 4. In general, sensitivity of dormant seeds of various plants to radiation is increased by either a low or a high water content.

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Peking, a high resistant variety to the soybean cyst nematode, was crossed reciprocally with incompletely resistant Nemashirazu and susceptible Shiromeyutaka. F₂ progenies of them were tested for the resistance, for which also relationships with some other characters were examined. Frequencies of the resistant plants were 1/4 for Peking X Nemashirazu, and near to 1/16 for Peking X Shiromeyutaka, thus, indicating one, for the former, or two, for the latter, recessive genes are concerned with the resistance. In these crosses a coupling linkage between the resistance and i allele which determine the exprcssion of seed coat color to black or brown was found. This resistant recessive gene was determined as “rhg₁”.

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F₂ and F₃ populations of hybrid between a Chinese variety, Reishiko, and a Japanese variety, Sekiyama 2, were analyzed. Reishiko has a dominant gene (Pi-k) controlling resistance to strains of the blast fungus. Ken 54-20 and P-2b, a dominant gene for colour of palea and lemma, glutinous endosperm gene wx, and a recessive gene for yellow seedling. Sekiyama 2 has a dominant gene (Pi-i) controlling resistance to strains of the blast fungus, P-2b and Ina 72, a dominant gene different trom one of Reishiko for colotlr of palea and lemma, non-glutinous endosperm gene Wx, and a recessive gene, different from one of Reishiko and functioning complementally with one of Reishiko, for yellow seedling. There are no linkage relationships among these genes found in both the varieties except of a linkage (26.9±8.5%) between gene for colour of palea and lemma, and gene for glutinous endosperm. This gene for colour of palea and lemma in Reishiko was considered to be same as C found in earlier studies.

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Mentha spicata L. (including M. viridis L. and M. Iongifolia (L.) HUDS.) can be divided into 4 groups in accordance with the number of chromosomes. That is, there are strains with 24, 36, 48 and 54 chromosomes in the somatic cells. In the present study, we took up the strains with 24 and 48 chromosomes as the subject of genome analysis. The strains with 24 chromosomes are given the genome formula RR like M. rotundifolia (L.) HUDS. In the strains with 48 chromosomes, there are two kinds of genome constitution. One is presumed to have RRSS, the other is RRS_cS_c, where S and S_c are partially homologous genomes. Genome constitution in M. spicata L. is found to have no connection with the hairiness of the mint plant, which BRIQUET used as a criterion for the classiflcation of species in the series ‘Silvestres’ ; nor does it have any connection with the crispness, of the leaves, though he established a special subspecies crispata BRIQ. in M. viridis L. and a special subspecies undulata BRIQ. in M. longifolia (L.) HUDS., based on this character. In two triploid hybrids RRS and RRS_c, some trivalent chromosomes can be seen in meiosis, so it is presumable that S and S_c are not entirely independent of R, but certain relations seem toexist between them. We also think that R grenome evolved into S_c and S_c into S. On the basis of this presumption, we tried to construct a family tree of the Spicatae section which included M. spicata and M. rotundifolia, as was shown in the Fig. 6.

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The seeds of two varieties Shfih6 and BR-No. 1 were irradiated with T-rays (60Co) of 15KR, and the leaf-blast resistance to physiological races N-1 and C-1 was analyzed genetically in the X5 gene-ration. Only susceptible mutations were obtained in both varieties. No relation could be fcund between the mutation frequency and X₁-panicle sterility. The mutation spectrum was very different between the varieties Shuho and BR-No. 1. The mutants derived from Shuho which revealed only the S-type symptom showed a wide range of variation in the number of S-type lesions. These lesions were assumed to be caused by polygenic and/or major-genic mutations. As for BR-No. 1, however, no polygenic mutations could be detected and all the mutants obtained showed only S-type lesions.. regarded as the result of the mutation of one or a few major genes. Experimental results suggest that the resistance of BR-No. 1 to race N-1 was controlled by one gene and the resistance to race C-1 was controlled by the simultaneous effect of two genes or the effect of epistasis of the two alleles originated in Shuho and Hokushin-Asahi. In spite of the S-type symptom, Shuho has a very stable field-resistance. The stability of this variety was discussed from the genetic point of view.

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When some Mendelian populations are grown successively under different conditions for several generations, they come to have diffcrent gene constitutions. The mechanism of this alteration has been mainly explained by occurrence of individual selection in the populations. It is said, however, that gametophyte selection may play an important role in this alteration. This study was conducted to clarify the existence of gametophyte selection by high temperature treatment of F₁ Spikelets of tworowed barley just before flovyering. Materials and characters used in this study are shown in Table 1, and these characters were ascertained to be controlled by one gene having no linkage relation among them. Several ears of one F₁ plant were put into warm water, 36-39°C, for 4 minutes just before flowering and the remaining ears of the plant were fertilized under natural conditions as the control. Segregation ratios of some qualitative c'haracters in F₂ generation of the former were compared with those of the latter. About 30 F₁ plants in each cross combination were treated. Segregation ratios of the four characters -awn type, lateral floret type, awn or awnless in lateral floret, and hair or hairless in leaf sheath- in monohybrid and dihybrid F₂ generations, agreed with the expected values in both cases of treament and control (cf. Tables 2, 3-a, -b, -c, 4, 5 and 6) .

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Variation in plant cells and tissues subcultured repeatedly in an artificial medium has been reported on many occasions. A well known case is the ‘habituation’' (GAUTHRET, 1955) of tissues which was caused by means of subculture in a medium containing a low concentration of auxin so that they became able to grow without the exbgenous auxin which had originally been required. In recent years, through repeated subculture on the same nutrient medium, several kinds of cfone have been obtained which differ from the original cultures in pigmentation, form, growth rate, and nutrient requirements (ARYA et al., 1962 ; Fox, 1963 ; STEWARD, 1963 ; BLAKELY et al., 1964 ; MURASHIGE et al., 1964). Also, the variation of totipotency in cultured tissues during the process of subculture has been reported. For example, a loss in the ability of the cultures to regenerate adventive buds and roots has been recognized (SKOOG et al., 1948 ; MURAS}IIGE et al., 1964). These kinds of variation in cultures are important problems that should be duly considered when the technique of tissue culture is being used. This paper reports the nature of the variation of totipotency in cultured tissues originated from carrot roots. In this experiment, it is also confirmed that the potency of regeneration in cultures dwindles to zero in the process of subculture, and that, on the other hand, there are hereditary differences in the totipotency of individual carrot roots.

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Ginger-lily is a kind of semi-hardy perennial plant for garden and cut flowers. There are also several wild species grown in India, Himalaya and the East Asian area. Recently the leading commercial varieties have been remarkably revived and increased by a few Japanese breeders, recovering from the miserable times of the last war when almost all of the flowering materials disappeared. After examining, since 1959, the chromosome number, pollen and seed fertility, flower type and other plant characteristics of a total of 36 commercial varieties of ginger-liiy, the author classifies them into the following three groups. ( 1 ) Twenty-four varieties, represented by Coronarium, are diploid (2n=34). The flowers are large, very fragrant but almost self-sterile due to self-incompatibility. The plants are somewhat dwarfed and usually produce many tillers. ( 2 ) Six varieties, reprcsented by Gardnerianum, are tetraploid (2n=68) and possibly allopolyploid-natured. The plants are rather erect and produce a few tillers. The flowers are small, scarcely fragrant, but bearing longer flower spikeswith plenty of fertile seeds. ( 3 ) The remaining six varieties, represented by Butterfly, are triploid (2n=51). They are perhaps hybrids between the above-described tetraploid and diploid varieties, showing intermediate characteristics in flower and plant habit,

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Among 10 plants of pansy (Viola Wittrockiana GAMS.) which were grown at Takii's Farm in 1950-51, 3 plants had 2n=55 chromosomes in somatic cells, 3 plants had 2n=52 and the remaining 4 plants 2n=54, 51, 50, and 49, respectively. Furthermore, some chromosomal irregularities were found in meiotic divisions of them.

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When there is dependency among environmental effects, if the variance of an individual unit is E, the variance of n individuals is not to be E/n. H. F. SMITH has suggested ernpirically that it should be E/n_b (0<__-b__-<1). In this paper, the author clears up the relation between a parameter of b and the concept of a correlation directly showing dependency and indicates the appropriateness, or the limit of the appropriateness, of SMITH'S assumption. Besides, it also proves that the above-mentioned fact for the variance is fit for the covariance when two or more characteristics are observed.

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