Stamens. Each stamen consists of a filament which carries an apical

Anther that contains 4 sacs of pollen grains.

3. Gynoecium: It is the female organ and is the central whorl of the flower

and consists one or more carpels. The carpel's base is swollen and called

Overy which contains the ovules. Carpels may fuse or remain separate

And enclose one or more locules. A thin neck attaches over the ovary

Called the style which ends by a sticky disc called stigma where pollen

grains adhere.

N.B.: Leaves of each whorl alternate with that of the next whorl.

Flower functions:

In order for the flower to perform its functions in reproduction and species continutiy, the stamens should prepare for pollen production, and the ovary for ovule formation. Then follows the 2 processes of pollination, and fertilization to produce the fruits, and the seeds.

First: Formation of pollen grains:

If you examine a T.S. in a mature anther of a large stamen as that of Lily plant, you will find 4 sacs of pollen grains. During flower development and before formation of pollen grains, these sacs are full of large nucleated diploid cells called spore mother cells (2N). The following steps take place:

Each spore mother cell (2N) is divided meiotically forming 4 haploid microspores (N).

Each of these microspores develops into a pollen grain through a mitotic division of its nucleus into 2 nuclei called the tube and the generative nuclei.

The wall of the pollen grain then thickens for protection. Meanwhile, the anther matures, and the wall in-between adjacent pollen sacs degenerates.

The sacs open releasing the pollen grains that disperse.

Second: Formation of ovules:

During the production of pollen grains in the anther, parallel changes occur in the ovary as follows:

The ovule starts to appear as a simple swelling on the interior ovary wall that contains a large spore mother cell (2N).

During the ovule growth, a funicle or umbilical cord develops connecting it with the ovary wall (through which food materials reach it). The 2 integuments surround the ovule completely, save a minute hole called micropyle, through which the ovule is fertilized.

The spore mother cell (2N) divides meiotically giving a row of 4 haploid cells (N). Three of them degenerate and the fourth grows rapidly forming the embryo sac, that is surrounded by a nutritive tissue called nucellus.

The nucleus of the embryo sac (N) is divided mitotically thrice giving 8 nuclei (N), 4 of them migrate to each pole of the embryo sac.

From each of these 4 nuclei, one moves to the centre of the embryo sac giving the 2 polar nuclei.

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