After fertilisation

After fertilisation, the flower turns into a fruit with seeds.

Endosperm first. The endosperm, a food store, develops before the embryo, so that the embryo has food ready. Usually the primary endosperm nucleus divides many times without walls forming, giving a free-nuclear endosperm, which later becomes cellular. A coconut shows both stages: the coconut water is free-nuclear endosperm, and the white kernel around it is cellular endosperm.

The embryo grows from the zygote, at the micropylar end. It passes through stages: proembryo, then globular, then heart-shaped, then mature.

• A dicot embryo has an axis with two cotyledons. The part above them is the epicotyl, ending in the shoot tip (plumule); the part below is the hypocotyl, ending in the root tip (radicle).
• A monocot embryo has one cotyledon. In grasses it is called the scutellum. The shoot tip is wrapped in a sheath, the coleoptile, and the root tip in another, the coleorrhiza.

The seed is the fertilised ovule. Its integuments harden into the seed coat, and the micropyle stays as a tiny hole that lets in water and oxygen when the seed sprouts. Seeds dry out and become dormant, which lets them survive until conditions are right.

• In some seeds, such as wheat and castor, the endosperm remains: these are albuminous seeds.
• In others, such as pea and groundnut, the embryo uses it all up during development: non-albuminous seeds.
• Occasionally part of the nucellus remains too, as a perisperm (black pepper, beet).

The fruit is the ripened ovary; its wall becomes the fruit wall, the pericarp. In some fruits, such as apple and strawberry, the thalamus also becomes part of the fruit: these are false fruits. Some fruits, such as banana, form without fertilisation and have no seeds: parthenocarpic fruits.

Apomixis is making seeds without fertilisation: a form of asexual reproduction that copies sexual reproduction. It is seen in some grasses. In some seeds, such as those of Citrus and mango, extra embryos grow from cells of the nucellus, so one seed contains more than one embryo: this is polyembryony.

Apomixis matters for farmers. Hybrid seed gives excellent crops, but if farmers sow seed from the hybrid crop, the next generation segregates and loses the hybrid's qualities, so new hybrid seed must be bought every year. If hybrids could be made apomictic, their seed would breed true, and farmers could keep using it.