Cytoembryological studies were employed to reveal the origin of haploid and to determine the cytological facters relating to the production of diploid polyembryony within one embryo sac occuring in natural population of a polyembryonic line SB- 1 of O. sativa L. The results showed that one or both synergids may develop into embryos prior to fertilization with frequencies of 2.24% and 1.75% in observed ovaries, respectively. The double fertilization was observed in embryo sacs with one previously-deve-loped multicellular synergid embryo. In caryopsis 3-8 d after anthesis, 1.62% abnormal slender embryos, which are morphologically different from zygotic embryos, were present between the endosperm Cytoembryological studies were employed to reveal the origin of haploid and to determine the cytological facters relating to the production of diploid polyembryony within one embryo sac occuring in natural population of a polyembryonic line SB-1 of O. sativa L. The results showed that one or Both synergids may develop into embryos prior to fertilization with frequencies of 2.24% and 1.75% in observed ovaries, respectively. The double fertilization was observed in embryo sacs with one previously-deve-loped multicellular synergid embryo. In caryopsis 3-8 d after anthesis , 1.62% abnormal slender embryos, which are morphologically different from zygotic embryos, were present between the endosperm