THE PARTS OF
A FLOWER

The typical flower develops at the tip of a flower stalk. The tip is somewhat enlarged, forming a cup-shaped structure called a receptacle. A bud grows from the receptacle and develops into a flower. Most flowers have four main parts: (1) the calyx, (2) the corolla, (3) the stamens, and (4) the pistils. The calyx is the outermost part of a flower. It consists of a set of leaflike or petallike structures called sepals. The corolla consists of a flower's petals. The stamens and pistils make up the reproductive parts of flowers. The stamens are the male parts, and the pistils are the female parts. Every flower has either stamens or pistils-or both stamens and pistils. Flowers that have all four main parts are called complete flowers.

Flowers that lack one or more of the parts are called incomplete flowers. In addition to the main parts, many flowers have glands that produce nectar. These glands, which are called nectaries, lie near the base of the flower.
In most flowers, each main part consists of three, four, or five elements or of multiples of three, four, or five elements. In a trillium, for example, three sepals form the calyx, and three petals form the corolla. The flower has six stamens, and the pistil is composed of three equal parts. The elements may be separate from one another, like the petals of a poppy or a rose. Or the elements may be fused (joined together). In flowers with fused petals, for example, the corolla is shaped like a tube, bell, trumpet, pouch, or saucer. Flowers that have such corollas include morning-glories, daffodils, and petunias. In such species as primroses and verbenas, the petals are fused at the base and free at the tip. The corolla thus has a tubelike or bell-like base and a fringed edge. In buttercups, morning-glories, and most other flowers, all the main parts are arranged around the center of the flower in a circular fashion. If the flower is divided in half in any direction, the halves will be alike. Such flowers are radially symmetrical. Orchids, snapdragons, sweet peas, and certain other flowers can be divided into identical halves only if the blossoms are cut through lengthwise. Such kinds of flowers are bilaterally symmetrical.

The calyx. The sepals, which make up the calyx, are the first parts to form among the majority of flowers. They protect the developing inner parts of the flower. In most cases, the sepals remain attached to the flower after it opens. In many flowers, such as buttercups and magnolias, the sepals are greenish, leaflike structures that are on the underpart of the flower. Other flowers have sepals that look like petals. Among many members of the iris, lily, and orchid families, the sepals and the petals look so much alike that they cannot be told apart. Botanists call these petallike structures tepals. Certain kinds of flowers have colorful sepals in place of petals. These flowers include anemones, hepaticas, larkspurs, and marsh marigolds.

The corolla, which consists of a flower's petals, is the showy, brightly colored part of most flowers. The colors of the petals-and of colored sepals-attract insects or birds that help spread a flower's pollen. The colors come from certain chemicals in a plant's tissues. These chemicals are often present in all parts of the plant, not only the petals or sepals. But they are masked in the other parts by large amounts of green or brown pigments. Many flowers also have spots, stripes, or other markings on their petals that attract insects or birds. In most cases, the odors of flowers come from oily substances in the petals. Strong odors, like bright colors, attract animals.

The stamens are the male, pollen-producing parts of a flower. They are not particularly noticeable in most flowers. In some cases, however, the stamens make up a flower's most attractive part. Male acacia flowers, for example, consist mainly of a large feathery tuft of colorful stamens. In most flowers, each stamen has two parts-a filament and an anther. The filament is a threadlike or ribbonlike stalk with an enlarged tip.

The enlarged tip forms the anther. The anther consists of four tiny baglike structures that produce pollen. After the pollen is ripe, these structures split open, which releases the pollen grains. The stamens are separate from one another in many flowers. But in such species as hollyhocks and sweet peas, some or all of the filaments are fused and form a tube around the pistil. In some flowers, the stamens are fused with one or more other flower parts. For example, the stamens of gentians are fused to the petals, and the stamens of most orchids are fused to the pistils