Pollen
Pollen grains, which contain the male gametes, are produced by the male part of seed-bearing plants. They are transported to the female part in different ways. Pollination of coniferous trees like spruce and pine is dependent on the spreading of these grains by wind and produce pollen in huge numbers. Although diluted when they become airborne, they can be numerous in the settled dust outside. Although pollen grains are frequently observed in indoor settled dust, they are found in very low numbers in indoor air samples. Several species produce pollen, which contains allergens. These substances are normally harmless to a person without allergies. People sensitive to allergens carried by pollen from certain plant species, will show allergic reactions when these particles are inhaled. Some of the pollen grains depicted below represent the most common allergy-developing species (inhalation-allergy). The pollen grains can be identified to plant family, genus or even species based on their unique morphology and surface structure.