1. The functional megaspore enlarges and develops into the embryo sac.
2. The nucleus of the functional megaspore undergoes mitotic division to form 2 nuclei.
3. These two nuclei move to opposite poles, forming the 2-nucleate embryo sac.
4. The nuclei divide again mitotically to form the 4-nucleate stage.
5. A third mitotic division produces the 8-nucleate stage.
6. These divisions are free-nuclear divisions, meaning:
   • Nuclear division occurs.
   • Cell wall formation does not occur immediately.
7. After the 8-nucleate stage, cell walls are formed, organizing the embryo sac.
8. Out of the 8 nuclei:
   • 6 nuclei are enclosed by cell walls to form cells.
   • 2 nuclei remain free in the central cell as polar nuclei.

Arrangement of Cells in Mature Embryo Sac

Micropylar End (Egg Apparatus)

9. Three cells are present at the micropylar end, called the egg apparatus:
   • 1 Egg cell
   • 2 Synergids
10. Synergids possess filiform apparatus (finger-like wall thickenings) which:
    • Guide the pollen tube into the embryo sac.
    • Help in nutrient transfer.

Chalazal End

11. Three cells are present at the chalazal end called antipodal cells.

Central Cell

12. The large central cell contains two polar nuclei.

Mature Embryo Sac Summary

• Total nuclei = 8
• Total cells = 7
  • 1 Egg cell
  • 2 Synergids
  • 3 Antipodal cells
  • 1 Central cell (with 2 polar nuclei)