(c) d (D (h) Figure 4 Embryo sac development and mature embryo sac structure of hybrid Guang-lu-ai4/O.alta.(a)Archesporial cell:(b)normal megasporocyte (c)megasporocyte with the nucleus in abnormal position:(d)abnormal degeneration of tetrad and no formation of functional megaspore:(e)functional megaspore degeneration:(f)embryo sac degeneration and nucellus tissue abnormal at embryo sac matured stage:(g)no organ formation in degener- ated embryo sac at embryo sac matured stage:(h)matured embryo sac in abnormal position. Biology of plant reproduction 8Biology of plant reproduction 18