After double fertilisation, the flower changes dramatically. Most parts are no longer needed and wither away, while the fertilised ovule becomes a seed and the ovary becomes a fruit.
From ovule to seed
Inside each fertilised ovule:
- the zygote divides by mitosis and grows into the embryo, made of the young shoot (plumule), the young root (radicle), and one or two seed leaves (cotyledons);
- the endosperm forms a food store (in many seeds the food is later moved into the cotyledons);
- the outer wall of the ovule (integument) hardens into the protective seed coat (testa);
- the ovule loses water, so the seed becomes dry and enters a state of dormancy.
From ovary to fruit
The ovary wall grows and develops into the fruit wall (pericarp), which encloses and protects the seeds. A fruit may be succulent (fleshy and juicy, like a mango) or dry (like a bean pod).
| Flower part | Becomes |
|---|---|
| ovule | seed |
| ovary | fruit |
| ovary wall | fruit wall (pericarp) |
| zygote | embryo |
| integument | seed coat (testa) |
Key idea
Seed = fertilised ovule; fruit = ripened ovary. The number of seeds in a fruit depends on the number of ovules that were fertilised in the ovary.
Example
In a papaya, many ovules in one ovary are fertilised, so the single fruit contains many seeds. The fleshy pericarp develops from the ovary wall.
Parts such as the petals, stamens, style and stigma usually shrivel and fall off, because their functions are complete once fertilisation has occurred. In some plants other parts of the flower also swell and become part of the fruit; an apple, for example, develops largely from the receptacle, forming what is called a false fruit.
The mature seed remains dry and dormant until it meets suitable conditions of water, oxygen and a warm temperature. Water is then reabsorbed, the enzymes and food store are reactivated, and the embryo resumes growth in a process called germination — the radicle emerging first to anchor the seedling and absorb water, followed by the plumule that grows upward to form the shoot.
Remember
Ovule → seed, ovary → fruit, zygote → embryo, ovary wall → pericarp. The seed becomes dry and dormant.