Description Bee pollinating a sunflower. Pollen is transferred from anther of one plant to stigma of another as bee collects nectar Pollen tubes are  unique to plants and their structures have evolved over the history of seed plants  . Pollen tube formation is complex and the mechanism is not fully understood, but is of great interest to scientists because pollen tubes transport the male gametes produced by pollen grains to the female gametophyte. Once a pollen grain has implanted on a compatible stigma, its germination is initiated. During this process, the pollen grain begins to bulge outwards to form a tube-like structure, known as the pollen tube. The pollen tube structure rapidly descends down the length of the style via tip-directed growth, reaching rates of 1 cm/h, whilst carrying two non-motile sperm cells. Upon reaching the ovule the pollen tube ruptures, thereby delivering the sperm cells to the female gametophyte , ultimately resulting in a double fertilization event  . The first fertilization event produces a diploid zygote and the second fertilization event produces a triploid endosperm. Pollen tubes are produced by the male gametophytes of seed plants. Pollen tubes act as conduits to transport the male gamete cells from the pollen grain—either from the stigma (in flowering plants) to the ovules at the base of the pistil or directly through ovule tissue in some gymnosperms. Pollen grains have separate structures such as microsporocytes and megasporocytes.
Description Bee pollinating a sunflower. Pollen is transferred from anther of one plant to stigma of another as bee collects nectar Pollen tubes are produced by the male gametophytes of seed plants. Pollen tubes act as conduits to transport the male gamete cells from the pollen grain—either from the stigma (in flowering plants) to the ovules at the base of the pistil or directly through ovule tissue in some gymnosperms. Pollen tubes are unique to plants and their structures have evolved over the history of seed plants since the Carboniferous period . Pollen tube formation is complex and the mechanism is not fully understood, but is of great interest to scientists because pollen tubes transport the male gametes produced by pollen grains to the female gametophyte. Once a pollen grain has implanted on a compatible stigma, its germination is initiated. During this process, the pollen grain begins to bulge outwards to form a tube-like structure, known as the pollen tube. The pollen tube structure rapidly descends down the length of the style via tip-directed growth, reaching rates of 1 cm/h, whilst carrying two non-motile sperm cells. Upon reaching the ovule the pollen tube ruptures, thereby delivering the sperm cells to the female gametophyte . In flowering plants a double fertilization event occurs . The first fertilization event produces a diploid zygote and the second fertilization event produces a triploid endosperm. Pollen grains have separate structures such as microsporocytes and megasporocytes.
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produced by the male gametophytes of seed plants. Pollen tubes act as conduits to transport the male gamete cells from the pollen grain—either from the stigma (in flowering plants) to the ovules at the base of the pistil or directly through ovule tissue in some gymnosperms. Pollen tubes are
A
since the Carboniferous period
R
, ultimately resulting in
. In flowering plants
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occurs
D
Pollen tubes are produced by the male gametophytes of seed plants. Pollen tubes act as conduits to transport the male gamete cells from the pollen grain—either from the stigma (in flowering plants) to the ovules at the base of the pistil or directly through ovule tissue in some gymnosperms.