Pollen is commonly released from the anther through a longitudinal slitlike opening in the anther wall. Other methods also occur. Dehiscence usually results from hygroscopic shrinkage of the anther wall. Change in humidity may cause repeated opening and closing of the pollen chambers. The pollen may be freed all at once or escape gradually.
The air dispersal of pollen and spores depends on various factors such as time of the day, variations in temperature and wind speed. On a bright sunny day, ascending air masses may bring bioparticles up to the convective layer.
The airborne pollen grains and spores may remain afloat in the atmosphere for a longer or shorter period depending on horizontal and turbulent winds, which prevent them from moving downwards gravimetrically (pollen rain). It is interesting to note that bio particles such as pollen and spores act as condensation nuclei in water drop formation. During this process, the precipitation helps in washing out atmospheric pollen and spores and thus effectively cleaning the atmosphere from air spora.
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