pollination

pollination, transfer of pollen from the male reproductive organ (stamen or staminate cone) to the female reproductive organ (pistil or pistillate cone) of the same or of another flower or cone. Pollination is not to be confused with fertilization, which it may precede by some time—a full season in many conifers. The most common agents of pollination are flying insects (as in most flowering plants) and the wind (as in many trees and all grasses and conifers), but crawling and hopping insects, snails, bats, primates, rodents, and hummingbirds may also serve. The devices that operate to ensure cross-pollination and prevent self-pollination (see sex) are varied and sometimes extremely intricate. Among them are different maturation times for the pollen and eggs of the same flower or plant, separate staminate and pistillate flowers on the same or on different plants, chemical properties that make the pollen and eggs of the same plant sterile to each other, and specialized mechanisms or structural arrangements that prevent the pollinating agent from transferring the pollen of a flower to its own stigma. In the lady's-slipper the bee enters the nectar-filled pouch by one opening and must leave by another; in so doing it brushes first past the stigma, which scrapes pollen off its back, and then past the stamens, which deposit another load of pollen. The stamens of the mountain laurel are bent back and held like springs by notches in the petals; when the bee alights it contacts the tall pistil and then, in probing deeper for nectar, triggers the stamens. Pollen is catapulted onto the insect's underside, ready for contact with the next pistil. Other examples of floral adaptations to their pollinating agents are the fig and its wasp and the yucca and its moth. Wind pollination, depending as it does on statistical chance for successful pollination, requires vast quantities of pollen, which may be forcefully ejected by the anther sac (as in grasses and ragweed) or may be exposed (as in cones and catkins) to the slightest breeze. See breeding.

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pollination

Transfer of pollen grains in seed plants from the stamens, where they form, to the pistil. Pollination is required for fertilization and the production of seeds. On the surface of the pistil the pollen grains germinate (see germination) and form pollen tubes that grow downward toward the ovules. During fertilization, a sperm cell in a pollen tube fuses with the egg cell of an ovule, giving rise to the plant embryo. The ovule then grows into a seed. Since the pollen-bearing parts of the stamens are rarely in direct contact with the pistil, plants commonly rely on external agents for pollen transport. Insects (especially bees) and wind are the most important pollinators; other agents include birds and a few mammals (notably certain bats). Water transport of pollen is rare. An egg may be fertilized by self-pollination (when the sperm comes from pollen produced by the same flower or by another flower on the same plant) or by cross-pollination (when the sperm comes from the pollen of a different plant).