Horse chestnut pollen grain. Coloured scanning electron micrograph (SEM) of a pollen grain from a flowering horse chestnut tree (Aesculus hippocastanum). The grain has three lobes, separated through deep furrows through which the pollen tube emerges at the time of germination. The characteristic surface of pollen grains is used by botanists to recognise and classify plants. 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: x1500 when printed at 10 centimetres wide.