Synonym: Flower pollen, Pollen grains
Pollen are the sex cells of flowering plants that fuse with the ovaries of other plants to fertilise them. They contain the haploid chromosome set. Pollen grains can reach other flowers in different ways: transmission through wind, water or small animals (such as birds or insects)are specified.
The size of pollen can differ greatly and can range from 5 μm (very light pollen) to 200 μm (very heavy pollen). However, the majority of the pollen has a diameter of 20 and 50 μm. The protoplast (cell membrane)of pollen is surrounded by a closed sporoderm. This pollen grain wall is generally composed of two superimposed layers:
- Intines: the thin inner layer has a low chemical reistance and is mainly composed of cellulose fibres.
- Exines: the chemically highly resistant outer sheath is produced from sporopollenin. Their resistance to physical and enzymatic influences is so effective that million year-old pollen grains can be isolated nearly undamaged in rock strata.
Pollen of all types of plants show characteristic pollen wall surface structures that enable a categorisation in the plant family and in parts to the type of plant. "Naked seeders"(gymnosperms) have smaller, lighter pollen with a surface structure that enables it to become airborne (suitable for transmission through the wind) and often feature air sacs. Enclosed seeds (angiosperms) have a highly differentiated sexine.
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