Answer: Endosperm is the nutritive tissue of angiosperm seeds formed from the triploid (3n) primary endosperm nucleus (PEN) produced by triple fusion. It nourishes the developing embryo.
On the basis of development there are three types:
- Nuclear endosperm: the PEN divides repeatedly by free nuclear divisions without wall formation, giving a large number of free nuclei in the central cell. A central vacuole is formed and the nuclei are pushed to the periphery. Later cell walls may form from the periphery towards the centre. Example: the liquid endosperm (coconut water) of coconut with multinucleate free nuclei, and the outer cellular white kernel; also maize, wheat, rice, sunflower. It is the most common type.
- Cellular endosperm: every division of the PEN is followed by cell wall formation, so the endosperm is cellular from the beginning. Examples: Petunia, Datura, balsam.
- Helobial endosperm: intermediate between the nuclear and cellular types. The first division of PEN is followed by a transverse wall forming two unequal cells, a larger micropylar cell and a smaller chalazal cell. Nuclear divisions then take place in both cells (free nuclear in the micropylar chamber), with walls formed later. It is common in monocots (order Helobiales), e.g. Asphodelus.
In some seeds (e.g. pea, bean, groundnut) the endosperm is completely used up by the embryo (exalbuminous seeds), while in others (castor, maize, coconut) it persists (albuminous seeds).
