雑種植物

1) According to the morphological standpoint of the plant, the cultivated varieties of rice may be classified in two different types : "Japonica" and "Indica." 2) Varieties of both types all have a high degree of self-fertility. This also true of hybrids resulting from varieties which belong to each type, that is, hybrids within the same type. On the other hand, the crosses of varieties of the "Japonica" type and those of the "Indica" type, namely the hybrids between the different types are very less fertile. 3) As to the formation of Pollen in hybrids w ithin the same type and in those between the different types, it is found very normal in the former, but in the latter it is extremely abnormal and the percentage of imperfect pollen grains is markedly great. 4) In the F2 generation , the degree of fertility of every strain within the same type was great, and almost alike to that of the parents or the F1 plants ; nevertheless, the fertility of the F2 plants from the hybrids between the different types was very low, deviation of the degree of their fertility being, however, very large. 5) All things considered, t h e cultivated varieties of rice can be classified into two types above named not only from the morphological standpoint, but also from the sexual affinity. These two types are, therefore, considered to be only distantly related in descent. 6) If we considered the dis t ribution of the "Japonica" and "Indica" types of cultivated rice, we shall find that the varieties native to Japan proper, Korea and Northern China all belong to the one, and that those native to Formosa as well as those of Southern China, India, Java, and other countries mostly belong to the other. Though in Central China rice is, for the most part of the "Indica" type, some varieties of the "Japonica" type are also found.