Passion flower pollen. Coloured scanning electron micrograph (SEM) of a pollen grain from the passion flower (Passiflora sp. ). This spherical pollen grain resembles a tennis ball, with three germinal furrows 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: x1800 at 6x6cm size.