Abstract
1) This paper deals with the results of crosses among ten species of Rubus, and of observations of genetic characteristics and cytological phenomena of the six F1-hybrids.2) The crosses of R. trifidus (2n=14) as the mother with the other diploid species were more successful than the crosses among the other species. And all the crosses of R. hirsutus (2n=14) as the mother failed to give hybrids. All the crosses between the polyploids and the diploids give no hybrid. Hybrids are obtained regardless whether the parents belong to the same subgenera or not.3) The characteristics of the parental species are inherited to the F1-hybrids in several distinct behaviours, which may be classified into four types: a) dominant, b) recessive, c) intermediate betwecen the parents, and d) hybrid vigor.4) In the fertile hybrids, R. trifidus×palmatoides, ribisoideus×palmatoides, ribisoideus ×Fauriei and palmatoides×Fauriei, the most frequent configuration of chromosomes is 7II at IM. While in the sterile hybrids, R. trifidus×hirsutus and trifidus× ribisoideus, univalents are offen observed at IM. When the univalents appear at IM of the sterile hybrids, the frequencies of occurrence of 6II+2I and 5II+4I are higher than those of the other configurations. The fertile hybrids have a large amount of normal pollen grains, but the sterile hybrids have less normal grains. The phenomenon of the latter may be due to the irregularities of meiosis.
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