Pollen. Coloured scanning electron micrograph (SEM) of a pollen grain of the garden hollyhock, Althaea rosa. Its outer wall (exine) has a spiky structure. When the pollen grain, containing the male gametes, lands on the stigma of a flower of the same species, it germinates. A pollen tube grows from the pollen grain & down to the flower's ovaries. The ovules are then fertilised & a seed is formed. Magnification: x200 at 6x6cm size.