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Pollen grains. Computer-enhanced image of a Scanning Electron Micrograph (SEM) of several different types of pollen grain. The size, shape and surface texture of these pollen grains is unique in each plant species. The sculptured outer wall (or exine) of the grain plays a role in it's dispersal by wind, water or insects. Pollen grains contain the male gametes of the plant which fertilize the female egg (or ovule) to form the plant seed. Pollen also causes allergies and hay fever. Magnification: approximately x1000 at 4.5x6cm size. (KEYSTONE/SCIENCE PHOTO LIBRARY/PASIEKA)