Callose deposits are present both in degenerating megaspores of the heteropolar tetrad in Oenothera hookeri and in degenerating embryo sacs of the homopolar developing tetrad in O biennis. They are partially continuous with the cell wall and partially enclosed in the degenerating cytoplasm and show electron opaque bands within a less electron opaque material Vesicles called callose grains are present in the degenerating cytoplasm of the embryo sac in O biennis These show an electron opaque fibnllar or granular core surrounded by a halo of low electron opacity Similarities in fine structure between callose deposits of female gametophytes which follow the degenerating pathway of development, and callose plugs present in pollen tubes during their growth, are discussed.Fil: Noher de Halac, Inés. Universidad Católica de Córdoba. Facultad de Ciencias de la Salud; Argentina