Pollination - jufun

This refers to the process in which pollen attaches to a specific location for fertilization in plants. In angiosperms, the stigma of the pistil is the site where pollen attaches, and in gymnosperms, the micropyle of the ovule is the site where pollen attaches. Pollination can be divided into self-pollination, where pollen attaches to the pistil of the same individual, and cross-pollination, where pollen attaches to the pistil of different individuals of the same species. Self-pollination can be divided into self-pollination, where pollen attaches to the pistil of the same flower, and necrofloral pollination, where pollen attaches to the pistil of different flowers on the same individual. Plants such as violets and morning glories are pollinated at the bud stage before the flowers open, which is called cleistogamy and is distinguished from anthesis pollination, where pollination occurs after the plant opens.

Generally, there are mechanisms to avoid self-pollination, such as bellflowers, magnolias, and plantains, where the maturation period of the pistil and stamen is delayed (dioecious), as in the case of hemp and ginkgo, where male and female plants are separated (dioecious), and where fertilization does not occur even if the pollen of the same individual is pollinated (self-incompatibility), and so on. In order to avoid self-pollination, plants try to pollinate with the pollen of other individuals. For this reason, insects, wind, birds, water, etc. are used as vectors for the movement of pollen. In insect-pollinated flowers, where pollen is carried to the pistil by insects such as bees, butterflies, and moths, there are many large, beautiful flowers that attract insects with their fragrance and nectar. In wind-pollinated flowers, where pollen is carried by the force of the wind, such as pines and cedars, there are many flowers that are not very conspicuous, and they produce large amounts of light pollen that is scattered into the air. Ornithophilous flowers, which are pollinated by small birds such as South American hummingbirds, are characterized by large, beautiful flowers and large amounts of nectar. There are also hydrophilic flowers such as Vallisneria, whose pollen is carried by water currents, and flowers whose pollen is carried by animals such as snails. Artificial pollination is when humans artificially place pollen on the stigma of the pistil to cause pollination, and is used to create varieties with superior genetic traits (breeding improvement), when there are no animals to mediate pollination, or to maintain pure lines.

[Seiichi Yoshida]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

植物の受精の際に、花粉が受精のための特定の場所につくことをいう。被子植物では雌しべの柱頭が、裸子植物では胚珠(はいしゅ)の珠孔部が花粉のつく場所となる。受粉は、花粉が同じ個体の雌しべにつく自家受粉と、同種の植物の別の個体の間で花粉が雌しべにつく他家受粉に分けられる。自家受粉には、同じ花のなかで花粉が雌しべにつく自花受粉と、同じ個体の別の花の間で花粉が雌しべにつく隣花受粉とがある。スミレやアサガオなどは、花が開く前のつぼみの段階で受粉するが、これを閉花受粉といい、開花してから受粉する開花受粉とは区別される。

　受粉には一般に自家受粉を避ける仕組みがあり、キキョウ、モクレン、オオバコなどのように、雌しべと雄しべの成熟期がずれたり（雌雄異熟）、アサやイチョウのように雄株と雌株が分かれたり（雌雄異株）、同一個体の花粉を受粉しても受精しない（自家不和合性）などの方法によって自家受粉を避け、他の個体の花粉によって受粉しようとする。そのため、花粉の移動を媒介するものとして昆虫、風、鳥、水などが利用される。ミツバチ、チョウ、ガなどの昆虫の媒介で花粉が雌しべに運ばれる虫媒花では、大形で美しい花が多く、香りや蜜(みつ)で昆虫を誘引する。マツやスギなどの風の力で花粉が運ばれる風媒花では、あまり目だたない花が多く、軽い花粉を大量に生産して空中に飛散する。南米のハチドリなどの小形の鳥によって受粉が媒介される鳥媒花は、大形の美しい花と大量の蜜が特徴となっている。このほか、セキショウモなどのように水の流れによって花粉が運ばれる水媒花や、カタツムリなどの動物によって花粉が運ばれるものもある。人が人為的に花粉を雌しべの柱頭につけて受粉させることを人工授粉といい、優れた遺伝的形質をもった品種をつくるのに利用されたり（品種改良）、受粉を媒介する動物がいない時期や純系を保つ場合などに行われる。

［吉田精一］

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