Fertilization

Fertilization, the union of haploid gametes resulting in a diploid zygote, may follow pollination, as shown in Figure 30-9. For fertilization to occur in angiosperms, a pollen grain must land on a stigma and then absorb moisture. The pollen grain will then germinate. Germination occurs when the nucleus of the tube cell causes the tube cell to form a pollen tube that grows through the stigma and style toward the ovary. The pollen tube grows to an ovule within the ovary and enters the ovule through the micropyle. After the pollen tube penetrates the embryo sac, two sperm (produced from the mitotic division of the generative cell in the pollen grain) can travel through the pollen tube and reach the egg. Unlike a gymnosperm's pollen tubes, an angiosperm's pollen tubes usually reach an egg a day or two after pollination.

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