Flowers attend us from birth to death. They lend joy to our celebrations, cheer our broken hearts, and add immeasurable color, scent, and form to our world. While we know that flowers are beautiful, we forget that they are also essential to our very survival.
Flower Function
Simply put, the task of a flower is to produce seeds through the sexual union (fusion) of male pollen cells and female egg cells. Seed formation is essential not only to the survival of the species of plant producing the seeds, but also to the many kinds of animals that depend upon seeds for food. The cells and tissues within the flower that lead to seed and fruit production are as important in many ways to humans and other form of animal life as are the activities of the green leaf.
Flowers are essentially modified branches bearing specialized appendages or floral organs. Some flower organs are borne singly on a stalk but in many cases, flowers are grouped in clusters called inflorescences. Sometimes what is commonly thought of as one flower is actually an inflorescence, as in the case of the sunflower, daisies, and chrysanthemums.
The arrangement of the flowers in the clusters determines the type of inflorescence, with many possible patterns: spike, raceme, panicle, umbel, head, and catkin. The type of inflorescence is often an important characteristic in classification.
Flower Structure
Flowers vary greatly in structure. The fundamental similarities among flowers of different kinds of plants are, however, greater than their differences, since all flowers have the same basic structural plan.
Each individual flower is borne at the tip of a specialized stalk known as a pedicel. The floral organs borne by the pedicel are usually grouped in four concentric whorls. Sepals make up the outermost whorl of floral organs. Sepals surround and protect the other parts of the developing flower. Petalsmake up the next whorl. Most animal-pollinated flowers have bright petals to attract the pollinators.
The two innermost whorls contain the reproductive structures. The male reproductive organs are the stamens. Stamens have two parts: a pollen sac (anther) on the end of a stalk (filament). An anther contains mirosporangia, which produce microsporesthat mature into pollen grains.
The innermost whorl contains the female reproductive structures, which are called carpels. One or more carpels fused together make up the structure called a pistil. The pistil is comprised of a swollen base called the ovary containing the ovules (eggs), the stalk-like style rising from the ovary, and the hairy or sticky pollen-trapping tip of the style known as the stigma. Flowers containing all four whorls are known as complete or perfect flowers.
Any flowers lacking one or more of the four whorls are termed incomplete flowers. Some types lack sepals or in the case of the tulips and lilies, the sepals are brightly colored and identical to the petals. Others may lack petals and possibly sepals as well. Members of the grass family all form incomplete flowers lacking both petals and stamens.
Grass flowers are so small and so drab due to lack of petals that most people aren’t aware they even exist. Or people don’t recognize them as flowers because they confuse flower and petal as being synonymous when they in fact are not.
Some flowers lack one set of sexual organs. Plants whose flowers have only male stamens but no female pistils are said to be incomplete staminate flowers. Those with pistils but lacking stamens are said to be incomplete pistilate flowers.
From the human perspective, the flower may well be the second most important plant structure on the planet (Leaves are undoubtedly the most important). Flowers produce the seeds that allow all the plant species we depend upon for our food, materials, medicine, and general comfort of life to continue to exist.
 |
