Pollination (redirected from pollinated)

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).

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Pollination

The transport of pollen grains from the plant parts that produce them to the ovule-bearing organs, or to the ovules (seed precursors) themselves. In gymnosperms, the pollen, usually dispersed by the wind, is simply caught by a drop of fluid excreted by each freely exposed ovule. In angiosperms, where the ovules are contained in the pistil, the pollen is deposited on the pistil's receptive end (the stigma), where it germinates. See Flower

Without pollination, there would be no fertilization; it is thus of crucial importance for the production of fruit crops and seed crops. Pollination also plays an important part in plant breeding experiments aimed at increasing crop production through the creation of genetically superior types. See Breeding (plant), Reproduction (plant)

Self- and cross-pollination

In most plants, self-pollination is difficult or impossible, and there are various mechanisms which are responsible. For example, in dichogamous flowers, the pistils and stamens reach maturity at different times; in protogyny, the pistils mature first, and in protandry, the stamens mature before the pistils. Selfing is also impossible in dioecious species, where some plants bear flowers that have only pistils (pistillate or female flowers), while other individuals have flowers that produce only pollen (staminate or male flowers). In monoecious species, where pistillate and staminate flowers are found in the same plant, self-breeding is at least reduced. Heterostyly is another device that promotes outbreeding. Here some flowers (pins) possess a long pistil and short stamens, while others (thrums) exhibit the reverse condition; each plant individual bears only pins or only thrums.

Flower attractants

As immobile organisms, plants normally need external agents for pollen transport. These can be insects, wind, birds, mammals, or water, roughly in that order of importance. In some plants the pollinators are simply trapped; in the large majority of cases, however, the flowers offer one or more rewards, such as sugary nectar, oil, solid food bodies, perfume, sex, an opportunity to breed, a place to sleep, or some of the pollen itself. For the attraction of pollinators, flowers provide either visual or olfactory signals. Color includes ultraviolet, which is perceived as a color by most insects and at least some hummingbird species. Fragrance is characteristic of flowers pollinated by bees, butterflies, or hawkmoths, while carrion or dung odors are produced by flowers catering to certain beetles and flies. A few orchids, using a combination of olfactory and visual signals, mimic the females of certain bees or wasps so successfully that the corresponding male insects will try to mate with them, thus achieving pollination (pseudocopulation).

While some flowers are “generalists,” catering to a whole array of different animals, others are highly specialized, being pollinated by a single species of insect only. Extreme pollinator specificity is an important factor in maintaining the purity of plant species in the field, even in those cases where hybridization can easily be achieved artificially in a greenhouse or laboratory, as in most orchids. The almost incredible mutual adaptation between pollinating animal and flower which can frequently be observed exemplifies the idea of coevolution. See Pollen