Abstract: 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.

Key words: Gossypium hirsutum, Micropyle, Ultrastucture, Pollen tube growth path