Male sex cell + Female sex cell = Zygote

Zygotes develop into offspring genetically different from each other, and from their parents.

The Male Reproductive Organ in a Flower 

The stamen is the male sex structure (male reproductive organs). Each stamen consists of the filament and the anther. Filament is a stalk-like structure that holds the anther. The anther contain pollen sacs which make and then release pollen grains. The pollen grains contain the male gametes.

The Female Reproductive Organ in a Flower

The carpel (pistil) is the female part of the flower. Each carpel consists of the stigma, style and ovary. The ovary is the swollen base of the carpel. It contains one or more ovules. The ovule contains the female gamete. The style is the stalk attached to the top of the ovary. The stigma is sticky, it receives the pollen grains during pollination.
 

The whole structure of a Flower

The sepals are (usually) green, leaf-like structures which protect the flower when it is in bud. The petals are the brightly coloured part of a flower. They attract insects to flowers, and so help in pollination. But if the flower is wind-pollinated, the petals are small and green, or not present at all.

Diagram of a microscopic pollen grain and pollen sac

                      Pollen sac                                                  Pollen grain

We all know that pollen grains are produced in the anthers of the stamens. The pollen grains contain the male gametes. These male gametes must reach the female gametes which are found in the ovules. For this to happen, the pollen grains must first be deposited on the stigma of a flower. This process is called pollination.
 

Pollination

Pollination is the transfer of pollen grains from the anther of a flower to the stigma of the same or a different flower.

Once in contact with a compatible stigma, the pollen grains takes up water from the cells of the stigma surface. After hydration, the pollen grain germinates, forming a pollen tube. The generative cell then divides into two sperm cells

Two Types of Pollination

In Self – pollination, pollen is transferred from the anther to the stigma of the same flower, or another flower on the same plant.

In Cross – pollination, pollen is transferred from the anther of a flower on one plant, to the stigma of a flower on another plant of the same species.

Cross-pollination is preferred from self-pollination because they can lead to cross-fertilization (outcrossing) and it is genetically advantageous. While self-pollination only leads to self-fertilization which reduces genetic diversity.
 

The two most common agents for carrying pollen are the wind and insects.

Wind and Insect – pollinated flowers have structural differences, adapted according to their method of pollination.

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You can view more details about this topic on websites listed below:

http://en.wikipedia.org/wiki/coevolution

http://www.mbgnet.net/bioplants

http://en.wikipedia.org/wiki/Flowering_plant

http://waynesword.palomar.edu/trmar98.htm