Marigold pollen grain. Coloured scanning electron micrograph (SEM) of a pollen grain from a marigold plant (family Compositae). Pollen grains display a great variation in their size, shape and surface texture. The outer wall (exine) is highly sculpted in many plants, as seen here, which may assist in dispersal. The characteristic surface of a plant's pollen grains is used by botanists to recognise and classify species. Each pollen grain contains a male gamete (reproductive cell) that is intended to fertilise an egg or ovule (female gamete), and initiate the formation of a seed for a new plant. Magnification: x1000 at 6x7cm size.