The micropyle of Gossypium hirsutum consists of an exostome and an endostome.On semithin serial transections, the exostome was visualized as a branched narrow gap except its outer and inner openings, whereas the endostome only a narrow linear gap. Ultrastructurally, the micropyle gap was formed by the integumental epidermal cells coated with a cuticle.The cells lining the micropyle gap were characterized by a large nucleus and abundant organelles as mitochondria, plastids, rough endoplasmic reticulum, vesicle secreting dictyosomes and small vacuoles.One or two pollen tubes were seen growing through the exostome and endostome gaps.Thus, the micropyle in cotton was basically a closed type as has been found in sunflower, but similar asymmetrical structural features were not observed.
