Flowers offer sensual interest to humans, but to a plant, its flower is nothing more than the means to produce offspring. The flower parts in the center of a blossom have specific roles in the process of pollination. Fertilization occurs inside the female flower part after pollination. Only after successful fertilization of a flower can seeds and/or fruits form on a plant.
Flowers are flowering plants' means to reproduce seeds, allowing subsequent generations of plants to endure. The sexual organs of a flower are the female pistil and the male stamen. Petals may or may not be present in flowers, but at least one sexual organ is always present. Plants with one gender flowers are called imperfect, while flowers with both male and female organs are dubbed perfect.
The male anther produces pollen in the anther, held atop a thin stem called a filament. Often there are many anthers in each blossom. The female pistil houses the ovule. The tip of the pistil is called the stigma, and the long neck connecting the stigma to the base of the pistil is called the style. An ovule may be singular or have many compartments, or carpels, within.
Pollination of the Flower
Pollination occurs only when flowers open. Pollen from the flower's male anther is released and via wind, insect or animal help, travels to rest upon the sticky style of the female pistil; this is the process of pollination. The color of petals or presence of nectar in the flower is a means to attract insect or animals to visit and facilitate the movement of pollen to the flower's style.
The Pollen Tube
Once pollen rests upon the surface of the style, enzymes are released and a thin pollen tube is created. The pollen tube allows the male sex cell of the pollen grain to travel through the tissues of the style to reach the ovule at the base of the pistil. Depending on plant species and number of ovules, one or hundreds of pollen grains create pollen tubes to travel to the ovules. The time needed for the pollen grain to form and travel the pollen tube can be as quick as one hour to several months.
Once the pollen tube reaches the ovule, the pollen's sex cells penetrates into the ovule. This fusion of male sex cells with the female sex cell is fertilization. Fertilization does not happen simultaneously at the time of pollination, but later after the pollen tube is formed and the male sex cell enters the ovule.
Fertilization results in seed formation. With male and female chromosomes joined, plant tissues differentiate to form a small plant embryo that is encased in the seed. A seed is surrounded and protected by ripening ovary walls that become fleshy fruits or hard, dry nuts.