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Ovule
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=== Megagametophyte === [[File:Embryosack Polygonum Lilium.png|thumb|500 px|Megagametophyte formation of the genera ''Polygonum'' and ''Lilium''. Triploid nuclei are shown as ellipses with three white dots. The first three columns show the meiosis of the megaspore, followed by 1-2 mitoses.]] [[File:Embryosac-en.svg|300px|thumb|Ovule with megagametophyte: egg cell (yellow), synergids (orange), central cell with two polar nuclei (bright green), and antipodals (dark green)]] The haploid megaspore inside the nucellus gives rise to the female [[gametophyte]], called the ''megagametophyte''. In gymnosperms, the megagametophyte consists of around 2000 nuclei and forms [[archegonium|archegonia]], which produce egg cells for fertilization. In flowering plants, the megagametophyte (also referred to as the ''embryo sac'') is much smaller and typically consists of only seven cells and eight nuclei. This type of megagametophyte develops from the megaspore through three rounds of [[mitosis|mitotic]] divisions. The cell closest to the micropyle opening of the integuments differentiates into the egg cell, with two ''synergid cells'' by its side that are involved in the production of signals that guide the pollen tube. Three ''antipodal cells'' form on the opposite (chalazal) end of the ovule and later degenerate. The large ''central cell'' of the embryo sac contains two ''polar nuclei''.
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