3.13—Fertilisation in flowering plants

In flowering plants, fertilisation follows pollination: a pollen grain germinates on the stigma and grows a pollen tube down the style to an ovule. Male nuclei travel through the tube and one fuses with the egg nucleus.

The tube grows towards the ovary, enters the ovule through the micropyle and releases the male nuclei. Fusion produces a diploid zygote; the sequence matters because pollen-tube growth delivers the nucleus to the egg rather than fertilising on the stigma.

A pollen grain can germinate only when the stigma is compatible. The tube then provides a continuous route from the pollen grain to the embryo sac, where nuclear fusion occurs.

Pollination is transfer of pollen; fertilisation is fusion of nuclei. Do not treat pollen landing on a stigma as completion of fertilisation.