Pollen grains. Coloured scanning electron micrograph (SEM) of pollen grains from a tiger lily plant (Lilium tigrium). Pollen grain size, shape and surface texture differ from one plant species to another. The outer wall (exine) of the pollen in many plant species is highly sculpted which may assist in wind, water or insect dispersal. This pollen sculpting is also used by botanists to recognise plant species. Pores in the pollen wall help in water regulation and germination. Pollen contains the plant's male gametes. These fertilise the eggs or ovules, initiating formation of plant seeds. Magnification: x638 at 6x7cm size.