Fertilisation and Post – Fertilisation Events
* Syngamy or first fertilisation involves the fusion of one male gamete with the egg cell present in the egg apparatus that result in the formation of a diploid zygote.
* Triple fusion involves the fusion of the other male gamete with the polar nuclei in the embryo sac that result in the formation of a triploid primary endosperm nucleus.
* Syngamy and triple fusion together comprise double fertilisation, a phenomenon unique to flowering plants.
Double fertilisation is followed by the following post – fertilisation events.
* Degeneration of the antipodals and synergids
* Development of the zygote into an emryo
* Development of the central cell into primary endosperm cell, which eventually develops into endosperm.
* In one of the three ways of endosperm development, the primary endosperm nucleus undergoes free – nuclear division to form free nuclei, which develop into endosperm following the formation of cell walls.
* The main function of endosperm is to provide nourishment to the growing embryo.
* The development of the embryo is called embryogeny.
Development of Fruit and Seed
* A fruit develops from a fertilised ovary.
* Parthenocarpic fruit develop from unfertilised ovaries.
* A fruit consists of pericarp and seed.
* Pericarp is the hardened ovary wall and a seed is a fertilised ovule.
* A seed is enclosed in a tough outer, protective covering called the seed coat.
* Inside the seed coat lie the emebryo, embryonal axis, endosperm and cotyledons.
* Certain seeds contain more than one embryo and are called polyembryonic seeds.
* Apoximis is a mechanism that allows a plant to produce seeds without fertilisation.