Passion flower pollen. Coloured scanning electron micrograph (SEM) of pollen grains of the passion flower (Passiflora sp. ). These spherical pollen grains resemble tennis balls, with three germinal furrows (two seen on grain at lower centre) dividing a highly- sculptured outer wall (exine). When the pollen grain, containing the male gametes, lands on the stigma of another passion flower, it germinates. A pollen tube grows out of one of the germinal furrows, growing down the stigma and into the ovary. The male gametes pass down the tube into the ovary where one fuses with an ovule (egg cell) to form a seed. Magnification: x800 at 6x7cm size.