. Explain the Types of endosperm
Types of endosperm: On the basis of development, endosperm are of three types :
1. Nuclear endosperm: In the nuclear type of endosperm development, the primary endosperm nucleus divides by repeated mitotic free nuclear divisions without the formation of walls. It results in the formation of a large number of free nuclei in the central cell of the embryo sac. A big central vacuole develops in the embryo sac pushing all the nuclei to the peripheral cytoplasm. Finally cell wall formation takes place from the periphery of the embryo sac towards the centre leading to the formation of cellular endosperm tissue. In Coconut, the endosperm is multicellular in the outer part and free nuclear in the centre. Nuclear endosperm is the most common type of endosperm and mostly found in polypetalae. e.g. Cotton, Zea mays, Capsella etc.
2. Cellular endosperm : In the cellular type of endosperm development, the first nuclear division of the primary endosperm nucleus is immediately followed by the wall formation. The first division results in the formation of two equal sized chambers : chalazal and micropylar chambers. The subsequent divisions are followed by regular cell wall formation. This type of endosperm formation is common in gamopetalae. e.g. Petunia, Datura.
3. Helobial endosperm : In the helobial type of endosperm development, the endosperm is intermediate between cellular and nuclear types. The division of primary endosperm nucleus is followed by wall formation and as a result two chambers : micropylar and chalazal chambers, are formed. Generally the chalazal cell does not divide further and function as haustorium. Nucleus of the large micropylar cell divides by repeated free nuclear divisions and further development takes place in the same way as the nuclear endosperm. Helobial type of endosperm development is prevalent in monocotyledons.