Pollen characters were studied in 44 diploid, seven triploid and two tetraploid culti-vars of Primula sieboldii. Pollen diameter was larger as was the ploid level higher. The higher frequency (more than 1.0%) of giant pollen (about 1.5 tirnes larger than normal pollen) and lower pollen fertility (less than 85%) were found in the triploid and tetraploid cultivars suggesting their usefulness for convenient identification of polyploid cultivars. Unconscious selection of polyploid cultivars might be accomplished because morphological gain, associated with polyploidy itself, matched well with the breeding objectives such as large flower and long peduncle, suitable for the traditional manner of appreciation of this plant. This situation is very similar to that of the development of tetraploid cultivars in other horticultural primulas, i. e., P. malacoides. P. sinensis and P. obcoleica.

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Sodium azide-induced damage in M₁ generation and mutation in M₂ Were analized in Japonica rice variety. In treatments of dormant seeds, germination rate and seedling griwtg were reduced in proportion to both the increase of sodium azide concentration and the prolongation of treatment time. Furthermore, sodium azide delayed the seed germination. When the extent of growth reduction and of the delay of germination were plotted against the "dose" (ConcentrationXSoaking duration) man entne lot of treat ments, these indices each fltted into a single "dose"-response curve. The higrhest frequency of chlorophyll mutation was 11.1 per cent per M₁ panicle and 1.22 per cent per M₂ seedling. With regard to mutation in agronomic characters, Iate heading, short culm, dwarf, and sterility appeared more frequently. In presoaked seeds, chlorophyll mutation was induced more frequently in the 6, 48 and 54 hour-presoaked seeds than 12 to 42 hour-presoaked seeds. However, M₁ seed fertility remained almost the same level (about 90 per cent) during this presoaking period. From these results, it appears that sodium azide when applied at the DNA synthesis stage of the first cell division of germinating process, is more effective in the induction of mutation. It also appears that the mutagenic action of sodium azide can be affected by cellular metabolism during germination.

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It is said that a fruit shape of most Japanese pear cultivars is round or oblate. But a wide variation in fruit shape existed before the native cultivars were cleared otLt by the two outstanding round or oblate shaped cultivars, Nijisseiki and Chojuro. Although most 'of those native cultivars have been already cut down, sketches or photos of Lruits are left :in literatures as the only track of the native cultivars at present. Using these sketches from 52 Iiteratures, the wide range of fruit shape variations of :349 Japanese pear cultivars (Pyrus serotina Rehder) were evaluated and were compared with those of two chinese pear species, 55 Chinese pear cultivars (P. Bretschneideri Rehder), and 23 Ussurian pear cultivars (P. ussuriensis Max.). The geographic differentiation and the historical changes of cultivars by breeding were clarified from the view-point of fruit =shape.

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Waxy (glutinous) and non-waxy isogenic lines of a rice cultivar, Taichung 65, which were established by TSAI and OKO (1965) after 17-time backcross recoveries of a hybrid with Taichung 65 (donor parent, a waxy variety, Kinoshita-mochi) were made available through the courtesy of the above two authors. In the present study, the waxy and non--waxy lines were compared with regard to the process of grain filling after anthesis. The materials were grown under four conditions each with two replications in a paddy field and a "vinyl-house" for two years. Heading date was recorded for each panicle, and the panicles were sampled to collect developing kernels. The number of kernels, and the fresh and dry weights of kernels were recorded. The grain-filling period was divided into. four stages. In the first stage (two weeks after anthesis), both water content and dry matter increased rapidly. In the second stage (the next two weeks), water content turned to decrease and dry matter deposited in the kernel increased rapidly, resulting in rapid decrease in percent water content. In the third stage (the following two weeks), water-content did not change much but dry matter increased slightly, percent water content decreasing gradually. The kernel attained the maximum dry weight at the end of this, stage. Thereafter, the kernel was naturally dried (the fourth stage).

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Using 18 strains, ranging from lax to dense panicle type, the principal component analysis was performed to elucidate the correlations among 17 characters relating to the panicle density. The first principal component extracted from the principal component analysis for whole strains, appeared to correspond to a number factor, and the second to a length factor. However, it was fcund that the flrst principal component extracted from the analysis for nine lax panicle type strains, was considered to be a number and length factor, being identical with the two principal components in whole strains. Furthermore, the first principal component, interpretable as a number factor, in the analysis for whole strains was resolved into the first three principal components in the analysis for six dense panicle type ones. In the scatter diagram fcr the related characters of panicle density, 18 strains could be classified into seven groups, each distinguishable on the basis of difference in the pattern of panicle formation. The result demonstrated that both the lax and dense panicle genes had manifold effects on the component characters of panicle density, thereby causing the large variation in the correlations among these component characters.

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In the breeding of rice, there is a need for an effective selection against pre-harvest sprouting. Two selection methods were tested with a hybrid population between non-dormant variety (P₁=Hokuriku 93) and dormant one (P₂=Koshihikari) in a greenhouse. during the rapid genaration advance of the breeding materials. First, F₃ seeds were classified by the germination speed into three groups, slow, moder-ate and fast. In F₄ seeds, the slowest germinating seeds were selected from the slow grop, moderately germinating seeds from the moderate group and the fastest germinating seeds Lrom the fast group. The same procedure as in F₄ Was repeated in F₅ seeds. The means of degree of pre-harvest sprouting of the three groups fairly corresponded to those of P₂, mid-parent and P₁ (Fig. 1). Second, F₃, F₄ and F₅ seeds were treated with high temperature at 70'C for 4 or 5 days, and the seeds survived were sown to raise next generation. There is a significant correlation between dormancy and to high temperature treatment. P₁ is a weakly dormant and low tolerant type and P₂ is a strongly dormant and highly tolerant type. This method was not so effective es the first one but showed a significant deviation toward the dormant parent (Fig. 1). Any adverse effect of the selection against pre-harvest sprouting was not observed on the other agronomic traits (Table 1). Correlations between pre-harvest sprouting and tolerance to high temperature treatment were observed in the F₆ Populations with P₁ and P₂ on both extreme sides (Table 2). It is inferred that the successful selection against pre-harvest sprouting was due to its high heritability. The heritability of the trait estimated by F₆ individuls and means of F₇ Iines was as high as that of culm length (Table 3). The importance and the merits of the selection against pre-harvest sprouting in early generations were discussed.

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In order to estimate the recombination of parental chrornosornes in the interspecifio hybrid progenies between Vicia pilosa (2n=14) and V. alcephicarpa (2 n=14), cyto-genetical studies were carried out. In F₁' all characteristic chromosornes of the parents were identified. The outer form of the F₁ plants was intermediate between the parents and the chromosome conjugation at MI of PMC showed 7_II or 6_II+2_I in large part of cells observed and some tetravalent chromosornes were observed. The fertility of the F₁ was extremely low. Backcross between the F₁ and V.pilosa was carried out, and in B₁F₁ and their later generation, four karyotypes of PP(2n=14). PTa(2n=14), PTa+ta₇(2 n=15) and TaTa(2 ri=14) were segregated. The degree of characteristic segregation between the plants within the strains was decreased in B₁F₃ than in the pre- ceding generation and there is the trend where certain identified chromosomomes retain the parental combinations, whereas some non-identified chromosornes readily formed recombinational karyotypes in the hybrid progenies.

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The silique of the plant in Cruciferae consists of two parts : the upper non-dehiscent part and the lower dehiscent, two-valved part. In Raphanus the upper part of the silique develops well, in which many seeds are contained. The lower part does not develop, usually containing no seeds. In Brassica, however, only the lower two-valved part develops and contains many seeds, the upper part being undeveloped. In the hybrid between Rapanus and Brassica, both parts of the silique develop. The ratio of length of the dehiscent part to the non-dehiscent part in the hybrid is dependent on the ratio of Brassica-derived chromosomes to Raphanus-derived chromosomes (KARPECHENKO 1928 ; TERASAWA 1933).

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Seeds of three kinds of rice varieties were treated with EI (O. 5%, v/v) and X-rays:. (25kR), then male-sterile mutants induced were screened in the M₂-M₄ generations. In the present study, the plants that showed complete sterility in self pollination without abnormality of female organ were defined as "male-sterile mutants". Anthers of those plants were indehiscent, containing few or no good pollen grains. The EI treatments yielded the male-sterile mutants all over the three varieties with the frequencies of 0.30-0.38%, totaling eight mutants, while the X-irradiation was ineffective in inducing the mutants. F₁ hybrids from the crosses between the mutants and their original varieties exhibited a normal seed fertility under self- and open pollinations. The segregation ratio in F₂ showed that the mutants, except one, were controlled each by a single recessive gene. Allelism test with those recessive genes revealed that at least six different loci were responsible for the different male sterilities. These results may indicate that EI treatment is highly effective in inducing male-sterile mutants and that a considerable number of loci are concerened with male sterilities in rice.

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Heading tirne of rice varieties are known to be controlled by three factors, thermo-sensitivity(X₁)' photo-sensitivity(X₂) and basic vegetative growth(X₃)' Degree of contribution of the three Lactors to the determination of growth duration from sowing to' heading was investigated. In the first experiment, 44 rice varieties were grown in a growth cabinet, the temper-ature of which was controlled so as to give a constant difference from the temperature of the open air. The measure of the three factors was obtained by growing plants in a growth cabinet with short(S:10h) or long(L:14h) daylength and low(L:20'C) or high(H:30'C) temperature. X₁, X₂ and X₃ are expressed by n_SL-n_SH, n_LL-n_SL and n_SH, respectively, where n_SL Stands for the number of days from sowing to heading in case of 10h and 20'C, and so on. Multiple correlation between growth duration(Y) and a set of X₁, X₂ and X₃ was. highly significant in all temperature levels, showing that the most part of varietal diffe-rences in growth duration can be explained by the three factors in combination. The standard partial regression coeffcient of Y on X₁, X₂ and X₃ revealed that photo-sensiti-vity(X₂) is most important in determining growth duration, followed by basic vegetative growth(X₃), thermo-sensitivity(X₁) showing no influence.

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For the purpose of establishing the chromosome map in rice plant, the locations of interchange break points and centromeres were determined by the pachytene analyses in reciprocal translocation heterozygotes and the F₁ hybrids produced by the crossings between two kinds of reciprocal translocation homozygotes in which one chromosome was involved in the two interchanges in common. The position of the centromere and the loci of ten marker genes and twenty-three break points were cytologically allocated in six kinds of chromosomes, i.e., the first, second, third, ninth, tenth and eleventh. The karyotype was estimated by measuring arm ratio and relative length in pachytene chromosomes. The authors propose to revise the correspondence of the number between the chromosome types and linkage groups.

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The seed germination of tobacco varieties, Xanthi and Zichina I, which had the same high dark-germination percentage at 25'C, was investigated under various temperature and light conditions. When tested at a high temperature of 35'C, Xanthi showed the light-requiring property, while seeds of Zichina I germinated well nearly irrespective of the light conditions. The participation of phytochrome system was suggested by the fact that red and far-red photoreversibility clearly observed in Xanthi and slightly in Zichina I at 35'C. The low dark-germinability of Xanthi at 35'C was partially dominant to the high dark-germinability of Zichina I, and the heritability value estimated Lrom a selection experiment in F₂ plants of the cross XanthiXZichina I was O.452.

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