Fertilisation of Flowering Plants

4. In the embryo sac the tube nucleus disintegrates and the tip of the pollen tube bursts releasing the two male nuclei.
1. A pollen grain lands on the stigma of a flower. The grain absorbs water and splits open.
2. A pollen tube grows out of the grain down the style. There are 3 nuclei in the pollen tube one at the tip and two male gamete nuclei behind it.
3. When the tube reaches the ovary it grows through the micropyle and into the embryo sac in the ovule.
5. One male nucleus fuses with the egg nucleus to make a zygote. This divides by mitosis to become the embryo of the seed.
6. The second male nucles fuses with 2 other nuclei - known as the polar nuclei at the centre of the sac. This produces a cell with a large nucleus which divides to become a food store called the endosperm for the mature seed.
7. A double fertilisation has taken place which only happens in flowering plants.

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