Each of the remaining 3 nuclei at both of the sac poles becomes enveloped by some of the cytoplasm and a thin membrane forming distinct cells.

The middle of the 3 cells that are close to the micropyle grows forming the egg (N). While the 2 side cells are called synergids. The 3 cells that are distant from the micropyle are called antipodal cells.

The ovule by such way becomes ready for fertilization.

Third: Pollination and Fertilization:

A. Pollination:

This is the process by which pollen grains are transported from the anther to the stigma of the flower.

Types of pollination:

1. Self pollination: The pollen grains are transported from the anther to the stigma of the same flower, or to that of another flower of the same plant.

2. Cross pollination: The pollen grains are transported from the flower anther of a plant to the stigma of another plant of the same species. This type of pollination occurs in plants according to presence of certain factors such as the following:

Flowers are unisexual.

Organs of one sex mature before those of the other sex (as in early maleness or early femaleness flowers)

Hight of anthers is lower than the stigma.

Cross pollination needs a means of transportation for pollen grains from one flower to another such as air, insects, water, or Man.

B. Fertilization:

This process takes place according to the following stages:

1. Pollen grains germination:

When the pollen grains fall on the stigma, they germinate where the tube nucleus (N) forms the pollen tube, which penetrates the stigma and crosses through the style till it reaches the ovule's micropyle. Then the tube nucleus degenerates while the generative nucleus (N) divides mitotically into 2 male nuclei.

One male nucleus (N) fuses with the egg nucleus (N) forming the zygote (2N), which starts to divide mitotically several times forming the embryo (2N).

The second male nucleus (N) fuses with the 2 nuclei of the embryo sac (the polar nuclei) (2N) forming the endosperm nucleus that become triploid (3N).

The last stage No.2 is called the triple fusion. While the two stages together No. 1 & No. 2 are callec double fertilization.

The endosperm nucleus (3N) is divided mitotically several times forming the endosperm tissue that supplies the early developing embryo with food. This tissue may remain outside the embryo occupying a part of the seed.

2. Formation of fruits and seeds:

Seeds are of two types:

a. Endospermic Seeds:

The embryo may keep the endosperm, the seeds in this case are called (Endospermic seeds) such as Monocotyledonous seeds, in which the integuments of the ovule and the ovary fuse together forming a single-seeded fruit (that is called a grain), as in Maize and Wheat.

b. Exendospermic Seeds:

The embryo may feed on the endospermic tissue during its development, so it is called (Exendospermic seeds) accordingly, the plant has to store another food in the cotyledons, hence these seeds are called Dicotyledonous seeds, where the integuments of the ovule harden forming the seed testa, it is called a seed. As in Beans and Pea seeds.

Events that take place after fertilization:

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