<i>Hisbiscus</i> 属植物に関する研究(第8報)

Abstract

1. F1 seeds and plants were obtained by interspecific crosses between three East-Asian species of Hibiscus, paramutabilis×syriacus, syriacus×paramutabilis and syriacus×sinosyriacus.2. Different strains of syriacus resulted in different vigor of the F1 plants in all of the three crosses. Only one out of the six strains used for cross pollination produced healthy hybrid plants which successfully reached maturity (Table 1).3. The color, form, size and number of flowers varied considerably even among the hybrid plants originating from the same combination of parents. Some of the hybrids seemed promising for ornamental purpose in that they had larger size and number of flowers than their parents (Table 2, Fig. I).4. The seasonal trends of flowering in F1 plants, of which mother plants were syriacus, showed a pattern more or less similar to that of syriacus or intermediate between those of the parents, while the hybrids originating from paramutabilis mothers produced the largest number of flower in August, when the parent species produced the least number (Fig. 2).5. The hybrid trees were largely similar to syriacus in their habit. The total number of flowers produced in a season tended to be greater in trees with bigger crown, but was little influenced by the number of current-year branches (Fig. 3).6. Hybrid plants were generally intermediate between the parents with respect to such morphological characters as the shape and size of leaf, flower stalk, peduncle and bractlet, the density of hairs on hairs on leaf surface, etc., though there were some exceptions (Table 3 and 5, Fig. 4 and 5).7. As compared with that of parents, the pollen of the hybrids was somewhat smaller in mean grain size, greater in size variation and lower in fertility (Table 6, Fig. 6).8. The meiosis was fairly normal in pollen mother cells of the three parent species, each having 40 bivalent chromosomes. In F1 cells, the sinapsis and tetrad-formation were also normal without any multipolarity and other serious abnormalities, though a few delayed univalents appeared in some cells (Fig. 7).9. Back-crosses with the parents were proved to be fertile. Viable F2 seeds were also obtained by reciprocal crosses between the F1 hybrids (Table 7, 8).