Post-fertilisation events

The essentials

After double fertilisation, the ovule matures into a seed and the ovary into a fruit. Endosperm development precedes embryo development so that the embryo has food. The most common type is free-nuclear endosperm, in which the PEN divides repeatedly without wall formation; later, walls form and it becomes cellular. The water of a tender coconut is free-nuclear endosperm and the white kernel around it is cellular endosperm.

The embryo develops at the micropylar end. The zygote forms a proembryo, then globular, heart-shaped and mature embryo stages. A dicot embryo has an embryonal axis with two cotyledons; the part above the cotyledons is the epicotyl (ending in the plumule) and the part below is the hypocotyl (ending in the radicle). A monocot embryo has one cotyledon, the scutellum; the radicle and root cap are covered by the coleorhiza, and the shoot apex by the coleoptile.

Key points

• Ovule → seed; integuments → seed coat; micropyle remains as a small pore; ovary → fruit; ovary wall → pericarp.
• Non-albuminous (exalbuminous) seeds have no residual endosperm (pea, groundnut); albuminous seeds retain it (wheat, maize, castor).
• Perisperm is persistent nucellus (black pepper, beet).
• False fruits develop from parts other than the ovary, such as the thalamus in apple and strawberry.
• Seeds can stay viable for very long; a date palm seed about 2000 years old has germinated.
• Significance: seeds store food, can be dispersed, survive unfavourable periods and carry new genetic combinations.

Common mistakes

• The seed coat comes from the integuments, not from the ovary wall.
• Coconut water is endosperm, not a fruit juice from the pericarp.