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| Fertilisation |
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| The pollen grains which reach the sticky stigma, absorb these secretions, swells up and ruptures at one of the germ pores. The thin intine emerges out in the form of a pollen tube which continues to grow and penetrates deep into the style. |
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| (A - E), A, a microspore of an angiosperm; |
| B E, stages in the germination of pollen grain and |
| development of male gametophytes |
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| The contents of the pollen grain move into the pollen tube. The tube nucleus moves first and comes to lie at the tip of the pollen tube. This is followed by the migration of the generative cell or the two male gametes if they have already formed. |
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| Longitudinal section of a flower showing germination of pollen grains and the phenomenon of fertilization. One pollen tube has grown through the style and has entered the embryo sac through the micropyle |
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| The pollen tube enters into the ovule, through the micropyle. Inside the embryo sac, the tip of the pollen tube ruptures and the 2 male gametes are set free near the egg apparatus. Inside the embryo sac, one of the 2 male gametes fuses with the egg nucleus and forms a diploid zygote. This process is called syngamy or true fertilisation. The other male gamete pushes further into the embryo sac and fuses with the secondary nucleus and gives rise to a triploid nucleus called the primary endosperm nucleus. This process of nuclear fusion is called triple fusion. |
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| This entire phenomenon of fertilisation involving the fusion of the egg and one of the male gametes, together with the union of the second male gamete with the secondary nucleus or the polar nuclei is called as double fertilisation. |
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| Longitudinal section of an ovule showing different stages of fertilisation |
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Reproduction in Flowering Plants
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