stigma the male gametophyte will continue to develop into a mature male gametophyte as follows: the pollen tube emerges from an aperture in the pollen grain wall and grows through the stigma and style; the tube nucleus is usually located near the tip of the pollen tube and the two male gametes are positioned behind the tube nucleus however, this order may be reversed in some species ; after reaching the ovary, the pollen tube may enter an ovule by several possible routes, most commonly through the micropyle and the nucellus