Megasporogenesis 
Megasporogenesis The details presented below are NOT those of Lily which has Tetrasporic Development. The example below is for Monosporic differentiation. The latter is easier to understand and is actually more typical for Flowering plants.
| 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 term means the
cell which forms a megagametophyte. The Megasporocyte enlarges and its cytoplasm is becomes very dense. The 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 later. 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 Cell with Four Nuclei. I hope that you were impressed by the use of thence! |
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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. |
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