Abstract
The reciprocal crosses were made between two Japanese representative lris species, I. elesata (2n=24) and I. Iaevigata (2n=32), which are highly devoid of afiinity each other, and the development of seeds was embryologically traced from 3 to 33 days after pollination to elucidate the cause of seed failure in process of development. Owing to the seed failure, no viable seed was obtained in either of the reciprocal crosses. In both crosses, the initial symptorn of the seed failure was the start of degeneration of endosperms, which appeared around 21 and 27 days after pollination in I. ensataXI. Iaevigata and I. IaevigataXI. elesata, respe. ctively. The degeneration of endosperm always occurred prior to that of embryos and was not accompanied with any abnormality in such maternal tissues as nucellus and integument. Moreover, it was substantiated by the success of embryo culture in I, IaevigataXI. ensata that embryos could develop normally when put on a suitable medium in place of abnormal endosperm. These findings drew a conclusion that the decisive cause for seed failure appearing in these reciprocal crosses is the degeneration of endosperm.
