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Megasporogenesis starts with the enlargement of one cell within a  diploid ovule. The term Nucellus is used to identify the diploid tissue within which the Megasporocyte develops. This latter term means cell which forms a megagametophyte.

The Megasporocyte enlarges and its cytoplasm is very dense. Its Nucleus enlarges in preparation for Meiosis.

The Integuments develop from the ovule epidermis just behind the Megasporocyte. These envelop the megagametophyte as it grows. However, they are incomplete and leave a Micropyle (small hole) through which the Pollen Tube enters.

Eventually, the Megasporocyte undergoes the first Meiotic Division which is a "Reduction Division"

Two Haploid Nuclei are thence created. These divide again to produce a Four Nucleate Cell.

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The four haploid Nuclei divide again to produce a cell with Eight Nuclei. This process is called Free Nuclear Division.

Following Nuclear migrations & cell formation, the
mature Megagametophyte (Embryo Sac) is formed.

It is typically composed of an Egg Apparatus (Egg + 2 Synergids) at the Micropylar end of the Megagametophyte.

A large, multinucleate Central Cell occupies most of the volume of the gametophyte.

Three Antipodals are found at the Chalazal end of the Megagametophyte.

 

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