Biology Semester II

Sections:

Introduction |  Section 1 | Section 2 | Section 3

Section Two:

Part 1 | Part 2 | Part 3 | Part 4 | Part 5 | Part 6 | Part 7 | Part 8 | Part 9

Biology: Flowering Plant Reproduction: Part Three The Receptacle The receptacle is the part of the stem where flowers are attached. In some plants, such as apple and cherry trees, the receptacle enlarges and becomes part of the fruit. Strawberries belong to a group of plants that have many small flowers on a prominent receptacle. Each of these flowers will produce a fruit (the strawberry pits) born on an enlarged, red receptacle (what we commonly call the strawberry, yummy). The Perianth The sterile (non-reproductive) parts of the flower are the sepals and the petals. In most plants, the sepals are green and quite leaf-like. In such plants, the sepals form the protective cover of the flower bud and open when the flower has developed to a sufficient degree. Plants, like Magnolias and Lilies, however, have sepals the same color as the petals. When there are only slight differences in shape and position between the sepals and petals, the outermost whorl of “petals” will be the sepals. When sepals and petals resemble each other to a high degree, they are termed tepals. The petals are usually the most visible, prominent part of the flower. For most of us, petals are what makes roses, petunias, or snapdragons so pleasing. The petal color attracts animals to the flower to accomplish pollination. Petals also produce scents that attract certain animals. Some plants of the taxonomic family, Sterculiaceae, are commonly known as carrion flowers because they emit an odor that smells like rotting meat. The flies that pollinate carrion flowers are scavengers that are drawn to this odor. Petals also may have an area that secretes a sugar-rich material, nectar. Nectar is often the “reward” insects and birds receive for visiting various flowers. The pollinators get a little nectar while moving pollen from one flower to another. The Androecium The androecium, the male part of the flower, consists of individual units called stamens. Each stamen is composed of a filament that supports an anther. The anther contains four microsporangia. These long, hollow structures produce microspores (otherwise known as pollen) by meiosis. The pollen grains mature within these structures. When the pollen is mature, the sporangium opens, releasing the pollen. Cross-section through a lily flower bud. Note the pollen grains developing inside the microsporangium (anther sac). Cross-section through young lily anthers. The pollen grains are the small dots inside the sacs. Stamens are thought to represent modified spore-producing leaves. In the 1950s, American botanist James E. Canright studied the evolution of flowering plants. He proposed that an evolutionary series connected the leaf-like stamens of primitive angiosperms (such as Magnolia) to less leaf-like stamens more commonly seen in modern plants (such as Lilium). Evolution of the stamen from leaf-like forms in “primitive angiosperms” to more “modern” types like the lily. Now go on to the next part.

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