This paper deals with the affinity of species in the genus Pinus according to the results of seed production in hybridizations. In inter-specific pollinations, Japanese red pine (Pinus densi-flora S. and Z.) and Japanese black pine (P. thunbergii PARL.), distributed in Japan and Korea were used as seed parents, and 19 exotic pine species were used as pollen parents. These seed parents belong to the subsection Sylvestres in the taxonomic classification of the genus Pinus. Sound seeds were obtained from the interspecific crosses among Asiatic species in the same subsection Sylvestres of the seed parent, but European species, although of the same subsection did not produce any sound seeds. In the crosses among the different
subsections attempted in this experiment, all combinations had a reproductive gap. Regarding the affinity of pines belong to the same group in the taxonomic classification of the genus Pinus, it is clear that some species; namely, P. densiflora, P. thunbergii, P. massoniana LAMB., P. taiwanensis HAYATA, P. tabulae-formis CARR., P. khasya ROYLE, P. luchuensis MAYR., and P. yunnanensis FRANCH. of the subsection Sylvestres distributed in the eastern Asian region have a close affinity.