Apertures are very small spots on the walls of a pollen, where the wall is thinner and/or softer. For germination it is necessary that the pollen tube can reach out from the inner of the pollen and transport the chromosomes to the egg deep down in the pistil. The apertures are the places where the pollen tube is able to break through the elsewhere very tough pollen wall.

The number and configuration of apertures are often very exactly defined for and characteristic for different groups of plants. The biggest class of plant species, Eudicotyledonae has three apertures in each pollen.

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