Development of the Female Gametophyte

            The development of the female gametophyte or the embryo sac occurs within the ovule, inside the ovary.  Each ovule contains a megasporangium which produces one megasporocyte.  The megasporocyte undergoes meiosis producing four haploid cells or megaspores.  Three of these disintegrate and the remaining megaspore divides mitotically three times.  The eight-nucleate, seven-celled structure  that is produced is the mature female gametophyte or embryo sac (Figure 15, 16).  Observe slide #44 illustrating the female gametophyte development.

Figure 15: Development of the Female Gametophyte (Embryo Sac).

  

   

                                       

Figure 16:  Development of the Female Gametophyte (Embryo Sac), a Microscopic View.

There are several important aspects of the gametophyte development in seed plants which you should particularly note:

            1)         no release of spores from the sporophyte.

            2)         small size of the gametophyte -- the small size of the pollen grains aids in transfer to the stigma; the small size of the embryo sac allows it to be better protected by the sporophyte.

            3)         neither antheridia nor archegonia are produced.

            4)         sperm nuclei rather than sperm cells are produced, eliminating the dependence on water.

The following chart summarizes the development of the male and female gametophytes.