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(8) POLLINATION, of pollen shed from anther to sigma of a pistil., divided into three types,, , (1) AUTOGAMY, Pollination is achieved within same flower, i.e.,, transfer of pollen from anther to the stigma of same, , | Transfer, | Pollination can be, , , , , , , flower. :, It requires synchrony in pollen release and stigma, , , , receptivity., Cleistogamous flowers (which do not open) are, invariably autogamous, eg. Viola (common, pansy), Oxalis & Commelina and provide assured, seed set even in absence of pollinators., These species also produce chasmogamous, flowers (with exposed anther and stigma) for, cross-pollination., (2) GEITONOGAMY, Transfer of pollen grains from anther to stigma of, another flower of the same plant., It is functionally cross pollination involving, pollinating agents, genetically it is similar to, autogamy, since the pollen grains come from the, same plant., (3) XENOGAMY, , 2 Transfers of pollen grains from anther to the, , stigma of a different plant., 2 This is the only type of pollination which brings, , genetically different types of pollen grains on the, stigma., , , , , , , , , , , , , , , , , , , , , , , OUTBREEDING DEVICES, , pollen tube growth in the pistil., © Production of unisexual flowers., , , , 2 Flowering plants have developed many devices to discourage self., Pollination and to encourage cross pollination. For example —, e Pollen release and stigma receptivity are not synchronised., e Anther and stigma are placed at different positions so that pollen, cannot come in contact with stigma of the same flower., ¢ Self-incompatibility is a genetic mechanism which prevents selfpollen from fertilizing the ovules by inhibiting pollen germination or, , 2 In castor & maize. (monoecious) autogamy is prevented but not, ey in papaya (dioecy), both autogamy and geitonogamy are, , (9) AGENTS OF POLLINATION, , ABIOTIC AGENTS, , 2 Pollen coming in contact with stigma is a chance, factor in both wind and water pollination. So flowers, produce enormous amount of pollen when compared, to number of ovules available for pollination. It is to, compensate loss of pollen grains., , Wind pollination, , 2 Requires light, non-stickly pollen so that they can be, transported by wind currents. Well exposed stamens, and large often-feathery stigma to trap air borne, pollen, single ovule in each ovary and numerous, flowers in an inflorescence. Tassels in corn to trap, pollen., , 2 Quite common in grasses., , 2 Pollination by wind is more common among abiotic, pollinations., , Water pollination, , 2 Pollination by water is quite rare, limited to 30 genera,, of monocotyledons e.g Vallisneria, Hydrilla, Zostera, (sea grass)., , 2 In majority of aquatic plants like water hyacinth and, , waterlily, flowers emerge above water & are, , pollinated by insects or wind., , In Vallisneria pollination takes place on the surface of, , water (epihydrophily), in sea grasses it takes place, , below water (hypohydrophily), , In most water-pollinated species, pollen grains are, , protected from wetting by a mucilaginous covering., , , , , , , , , , , , , , entry of pollen tube., , , , , , 2. BIOTICAGENTS, , 2, , (41) POLLEN-PISTIL INTERACTION, , The ability of pistil to recognise the pollen followed by its acceptance or rejection is the result of a, continuous dialogue between pollen grain and the pistil. Its a dynamic process., , This dialogue is mediated by chemical components of the pollen interacting with those of the pistil., Following compatible pollination, pollen tube grows through the tissues of the stigma and style, the, contents of pollen grain move into pollen tube., , The growing pollen tube carrying two non-motile male gametes, reaches the ovary, enters the ovule, through micropyle & then enters one of the synergids through the filiform apparatus, which guides the, , pollinating agents-Bees, butterflies, flies, beeties,, wasps, ants, moths, birds (sunbirds & humming birds) & |, , bats., , Majority of flowering plants use a range of animals as i, }, , Among animals, insects particularly bees are dominant, pollinating agents., , , , Some primates (lemurs), arboreal (tree dwelling), rodents or even reptiles (gecko lizard & garden lizard), are also pollinators in some species., , Insect-pollinating flowers are large, colourful, fragrant, and rich in nectar. Small flowers are clustered in, inflorescence to make them conspicuous., , Animals are attracted to flowers by colour and/ or, fragrance., , Flowers pollinated by flies & beetles secrete foul odours, to attract these animals., , Nectar & pollen grains are usual floral rewards., , In some species floral rewards are in providing safe, places to lay eggs, eg, Amorphophallus; A species of, moth and Yucca - cannot complete their life cycles, without each other., , , , , , , , , , , , , , All these events - from pollen deposition on the stigma until pollen tubes enter the ovule - are together, referred to as pollen - pistil interaction.