Evening primrose pollen. Coloured scanning electron micrograph (SEM) of the surface of a pollen grain from an evening primrose (Oenothera sp.) flower, showing the characteristic threads secreted by the pollen grains to hold them together in packages and probably to aid in attachment to insect pollinators. Pollen grains are the male sex cells of a flowering plant. Magnification: x2200 when printed at 10 centimetres wide.