ABSTRACT
Formation of the operculum commences during embryo sac development and is normally preceded by an increase in number of cell layers at the inner integumental apex. Subsequently epidermal cells on the outside (Costaceae-Panchaksharappa, 1962; Lemnaceae-Kapil and Vasil, 1963) or on the inside (Liliaceae-Shamrov, unpublished data) dramatically increase in size, especially in the radial direction. Either the entire apical portion of the inner integument develops into an operculum (Lemnaceae-Kapil and Vasil, 1963; and others) or only its individual layers (Zosteraceae-Teryokhin and Shibakina, 1985). In doing so, the cell walls increase in thickness and the subjacent integumentary cells are gradually crushed and lignified. The operculum reaches maximum development in a mature seed, providing protection for the micropylar region of the seed and aiding in germination.
