Formation of female gametes:
- Ovule develops from a cushion like part of the ovary called the PLACENTA. Ovule is connected to the placenta by a stalk known as FUNICLE.
- The tissue enclosed inside the ovule is NUCELLUS. It is surrounded by two coverings or INTEGUMENTS which leave a small pore known as MICROPYLE.
- Basal part of ovule where the two integuments arise is known as CHALAZA.
- From the cells of the nucellus, one cell differentiates as MEGASPORE MOTHER CELL which is diploid (2n).
- The megaspore mother cell divides by meiosis to form four megaspores out of which only one develops as embryo sac. This is haploid and is also called Female Gametophyte.
- At the time of fertilisation there will be a total of 7 cells arranged in three groups in a mature embryo sac.
- They are one egg, two synergids, one central cell three antipodals.
- While all the cell are in haploid condition only the secondary nucleus is diploid.