Cactus pollen. Coloured scanning electron micrograph (SEM) of a pollen grain of an Echinopsis sp. cactus. Pollen grains contain male gametes, which fertilize the ovules of a plant, initiating the formation of plant seeds. The outer wall (exine) of a pollen grain is highly sculpted in many plants, which may assist in their dispersal by adhering to pollinating insects. The structure of the exine is used to identify pollen from different plants. Magnification: x1100 when printed 10cm wide.