18.6: Female gametes develop in embryo sacs.

Production of the female gametes (eggs) doesn’t cause the suffering in humans that pollen grains do, primarily because the production is confined to the closed structure of the ovary. Within the ovary, one or more diploid cells differentiate into ovules. Each ovule is made of outer protective cells that surround a diploid, egg-producing cell called a megaspore mother cell. The megaspore mother cell undergoes meiosis to produce haploid megaspores. Within the ovule, three of the haploid megaspores disintegrate, and the remaining one undergoes mitosis several times to produce the embryo sac, the structure in which fertilization will occur (FIGURE 18-15). The embryo sac is an unusual collection of seven cells. Six of these cells—including the one that is the egg—have haploid nuclei, and the seventh cell, called the central cell, has two distinct haploid nuclei. The embryo sac waits for a male gamete to arrive.

Figure 18.15: Female gametes are produced within the ovary of a flower.