ENDOSPERM

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         During fertilization one male gamete (n) fuses with the secondary nucleus (2n) to form a triploid nucleus (3n) known as primary endosperm nucleus. It divides repeatedly giving rise to a large number of very small nuclei. Some amount of cytoplasm is being deposited around each of the nuclei followed by wall formation and the whole mass of cells is known as endosperm which completely fills up the nucellus.
            TYPES OF ENDOSPERM
            On the basis of behavior of primary endosperm nucleus (PEN), the endosperm may be divided into the following types –
            1. Nuclear type:- This is the most common method of endosperm development. Here the primary endosperm nucleus undergoes free nuclear divisions for several times, without any wall formation. As a result several thousand nuclei are formed which lie in the cavity of the central cell. These nuclei may be consumed by the embryo or they may become cellular at the later stage in centripetal manner. Example – French bean, Garden nustertium, Madar, etc.
            2. Cellular type:- In some plants cell division of the PEN is followed by the wall formation, so that the endosperm is formed at once. But the direction of the formation of first wall with respect to the embryo sac may be different. In Adoxa, the first wall is longitudinal. But in Custard apple it is transverse and in Heliotropium the first wall formation is oblique.
            3. Helobial type:- This type is intermediate between cellular and nuclear type. Here the first division of the PEN is followed by a transverse wall resulting in a micropylar and chalazal chamber. Further divisions are generally free nuclear and may be formed by the micropylar chamber only. Indian balsam (Impatiens) is an example of this type.
            FUNCTIONS OF ENDOSPERM
            1. Endosperm provides nutrition to the growing embryo.
            2. In albuminous seeds, the germinating embryo gets nourishments from the endosperm.
            3. Endosperm is also rich in many plant hormones like gibberellins, cytokinins, etc.
            4. It also regulates the precise mode of embryo development.
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