1 4. In the embryo sac the tube nucleus disintegrates and the tip of the pollen tube bursts releasing the two male nuclei.
2 1. A pollen grain lands on the stigma of a flower. The grain absorbs water and splits open.
3 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.
4 3. When the tube reaches the ovary it grows through the micropyle and into the embryo sac in the ovule.
5 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 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
7 7. A double fertilisation has taken place which only happens in flowering plants.