Pollination rigida", this allows the plant to self-pollinate, which is useful when biotic pollinators in the environment have decreased. It is possible for a plant have varying pollination methods, including both biotic and abiotic pollination. The orchid "Oeceoclades maculata" uses both rain and butterflies, depending on its environmental conditions. More commonly, pollination involves pollinators (also called pollen vectors): organisms that carry or move the pollen grains from the anther of one flower to the receptive part of the carpel or pistil (stigma) of another. Between 100,000 and 200,000 species of animal act as pollinators of the world's 250,000 species of flowering
Pollen to pollen is called pollinosis, and allergy specifically to grass pollen is called hay fever. Generally, pollens that cause allergies are those of anemophilous plants (pollen is dispersed by air currents.) Such plants produce large quantities of lightweight pollen (because wind dispersal is random and the likelihood of one pollen grain landing on another flower is small), which can be carried for great distances and are easily inhaled, bringing it into contact with the sensitive nasal passages. Pollen allergies are common in polar and temperate climate zones, where production of pollen is seasonal. In the tropics pollen production varies less