The nucellus of cotton (Gossypium hirsutum) contains a column of specialized cells which degenerate before the pollen tube reaches the nucellus. The pollen tube grows between the walls of these degenerate cells. The growth of the pollen tube crushes most of these cells but does not cause the degeneration of additional nucellar cells. An electron-dense material is found in the nucellar cell walls associated with the growth of the pollen tube for about one-half the thickness of the nucellus. This material appears to spread in a wave-like fashion from the tube through the walls of the nucellar cells. Both the walls and cytoplasm of the cells do not appear changed after the passage of the material. The dense material never reaches the embryo sac itself.