Heterosis originally occurs in plant weight at early stage of growth and is transmitted to other vegetative characters through the path of developmental correlation of characters. High yield of hybrids may be expected at non-economical with spacing or in genetic mixture, but it may not be expected in pure stands densely planted.

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Reciprocal crosses were made between Pelarganium denliculatum, 4x and P.roseum 4x, and 51 hybrids were obtained. The variation of different plant characters among the F₁ hybrids, such as capsule length, seed size, growth habit, leaf shape, flower shape and flower colour, was examined. The hybrids ranged between both parental species in each of the above-mentioned morphological characters. Signiflcant differences were found in both the number of essential oil glands and the yield of oil among the hybrid plants as well as among sampling dates. The components of essential oil in the hybrids were approximately intermediate between both parents.

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Relationships between nuclear volume, nuclear DNA content and radiosensitivity were studied on genera of a family, species of a genus, and strains a species. Throughout the materials observed the radiosensitivity was more markedly correlated with the mean DNA content per chromosome than with the estimated interphase chromosome volume. Data involved information about an appreciable reduction in nuclear DNA cdntent in cultivated polyploid plants associated with a proportional reduction in radiosensitivity.

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Cytogenetical studies of Mentha aquatica L. with 96 chromosomes were carried out by the aid of the interspecific crosses with 4 mint species including 7 strains of the known genome constitutions. It was concluded that the genome constitution of this mint species was R^aR^aSSJJA⁵qA⁵q. In addition, a genealogical tree of the subgenus Menthastrum was tentatively presented on the basis of the results obtained so far.

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Two Western White wheat varieties, Gaines and Omar, were tested at Fukuyama, southwest Japan for quality and agronomic characteristics in evaluating them as cross parents for flour color improvement of Japanese wheat. Late heading was an obstacle, as the ripening period extends to the rainly season and grain quality is impaired.

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Many of the ovules excised 4∼5 days after anthesis could develop to mature seeds on Nitsch's medium containing yeast extract and NAA. On the othef hand, some mature seeds were obtained from the young ovules excised immediately after fertilization, only when they were cultured on the medium supplemented by fruit juice prepared from young fruit of cucumber or water melon.

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This investigation was conducted to obtain informations for combining ability in F₁ hybnds of “MS-HE” (male-sterile grain sorghum × hegari group) combinatlon type and to get any suggestlon for the future breedmg program of “MS-HE” type. Experimental results indicated that in screening varieties and lines for use in the hybrids of “MS-HE” combination type, the greatest progress could be made by selecting varieties or lines on the basis of their general combining ability.

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Recently, Ixia is grown on a small scale for cut-flowers in oup country. Twenty-two commercial varieties were used to examine the somatic chromosome numbers, fertility, and other habitual characteristics. Six varieties were diploid (2n=20), 8 triploid (2n=30) and the rest were tetraploid (2n=40). Tetraploids, as well as most of the triploids, had larger flowers and prettier colors, and showed considerably higher fertility than diploids. Some varietal and inter-specific crosses succeeded in the mixed state with diploids, triploids, and tetraploids levels. So, it was assumed that these tetraploids and triploids would be of allopolyploid constitutions.

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