• In a young anther each of the four pollen sacs contains many large diploid (2N) spore mother cells (pollen mother cells).

1. Each spore mother cell divides by meiosis to form 4 haploid (N) microspores.
2. Each microspore’s nucleus divides mitotically into two nuclei: the tube nucleus (large) and the generative nucleus (small). The cell is now a pollen grain with a thick, protective wall (an outer exine and inner intine).
3. The wall between adjacent pollen sacs breaks down; the anther opens (dehisces) and the pollen grains are released, ready to be dispersed.

1. the ovule becomes the seed:
2. the zygote → embryo (plumule, radicle, cotyledons);

the fertilised central cell → endosperm;

• the integuments → seed coat (testa), hard and protective;
• the micropyle stays as a small pore through which water enters at germination;
• the synergids and antipodals disappear.
• Types of seeds, according to the endosperm:

• The fruit:
• after fertilisation the calyx, corolla, stamens, style and stigma wither and drop; only the ovary remains, which grows, accumulates food and ripens into the fruit, under the effect of auxins secreted by the developing seeds/ovary.
• The ovary wall becomes the pericarp and the ovule wall (integuments) becomes the testa.
• Some fruits keep parts of the flower calyx and stamens in pomegranate; calyx in eggplant (and date); corolla remains in marrow (courgette).
• False (accessory) fruit a fruit in which a part of the flower other than the ovary enlarges and stores food — e.g. the receptacle in apple.
• If pollination and fertilisation do not occur, the flower withers and falls off without forming a fruit.
• Role of pollination in fruit formation pollination provides the male nuclei for fertilisation; it also stimulates the formation of auxins necessary for the ovary to grow into a fruit, even without fertilisation.
• Parthenocarpy:
• natural formation of seedless fruits because fertilisation has not occurred (banana, pineapple, some oranges).
• It can be induced artificially by spraying the stigmas with extract of pollen grains (pollen powder in ether) or with synthetic auxins (indole acetic acid or naphthalene acetic acid), which stimulate the ovary to develop into a fruit with no seeds.

• The ripening of fruit and seeds often stops the growth of the plant and may lead to its death, especially in annual plants, because of the consumption of stored food and the inhibiting hormones.

✍️ Worked examples

• Worked example 8.
• A gardener sprays naphthalene acetic acid on tomato flowers that were never pollinated, and gets seedless fruits.
• Why?
• The synthetic auxin replaces the natural auxin normally produced after pollination/fertilisation, stimulating the ovary wall to grow into a fruit.
• Worked example 9 (which parts?).
• In a pea pod the pod is the pericarp (ovary wall); the peas are seeds (ovules); the seed coat is the integument; the large fleshy part inside is the cotyledon; no endosperm remains (exalbuminous).
• In a wheat grain the grain is a fruit and seed fused; the white floury part is the endosperm.