Abstract
1. Tetraploids induced from various varieties of Eastern Asia were crossed with certain tetraploid varieties, and fertility, good pollen percentage, plant height and other characters in the F1 plants were observed. Kamo's castration method was used and F1s of 121 different variety combinations were obtained.
2. The F1s were generally higher in fertility than the parental varieties, though different according to the variety combination. Those having high fertilities were to some extent larger in number among variety combinations between the Continental and the Insular groups. And fertility in tetraploid hybrids seemed to correlate slightly negatively with the fertility in the corresponding diploid hybrids.
3. In the percentage of good pollen, though the above-mentioned phenomena were not seen, a number of variety combinations showing high good pollen percentages on tetraploid level were found among those sterile on diploid level. Good pollen percentage was found to correlate with the fertility in seed setting.
4. F1 plants were generally vigorous in growth, and tended to be higher than the parental varieties. This tencdency seemed to be remarkable in the crosses between the Continental and the Insular groups. And the ratio of the plant height of F1 to the average of parents was found to correlated with fertility. Considering these phenomena, the rise of fertility in the F1 seems in a greater part to be due to the complementary effect of genes of parental varieties.
