Throughout most of the world, spring and summer bring a tumult of colorful flowers that burst into brilliance in both gardens and wild spaces. People appreciate flowers for the beauty they lend the world around them, but from the plant's perspective, flowers have a much more important reason for existing. Flowers help plants to fertilize the seed and protect the seed as it develops, allowing flowering plants to flourish throughout the world.
Flowering plants are the most successful and evolutionarily advanced plants on Earth. With more than a quarter-million species alive today, they have succeeded where less advanced plants have not, thanks to the flower. Before plants developed flowers, they required mechanical methods of fertilization, relying on water and wind to bear their spores or pollen to another plant. When fertilization is successful, the seeds produced by nonflowering seed-bearing plants are rudimentary compared to the seeds of flowering plants and less able to handle the stresses imposed on developing seeds.
Flowers act as reproductive structures for plants, housing both male and female parts and producing pollen and seeds. The most familiar and noticeable part of the flower is its petals, which are brightly colored, scented and sometimes patterned in order to attract pollinators. Emerging from the center of the flower is a single structure called the pistil, surrounded by smaller, filamentous structures called stamens. The pistil is the female structure that collects pollen, while the stamens are male structures that produce pollen. Following the pistil into the flower, you encounter the ovary, where fertilization occurs and seeds form.
Flowers use colors and scents to attract bees, butterflies, hummingbirds and other pollinators that, when they delve into the flower to feed, become dusted with the flower's pollen in the process. As these pollinators move from flower to flower, the pollen that collects on their bodies sticks to the pistil of later flowers that they visit, fertilizing the eggs inside the plant's ovary. Nonflowering seed-bearing plants, which include such species as conifers and palm trees, in contrast, must wait for the wind to bear their pollen to the appropriate species. Flowers allow for much more deliberate pollination and tend to be more successful as a result.
Once pollen sticks to the pistil, a pollen tube descends into the plant and releases sperm into the ovary, fertilizing the egg and producing seeds. The ovary protects the young seeds as they develop. Nonflowering seed-bearing plants do not have ovaries, and their seeds are unprotected as they develop and are more susceptible to harm.
Seeds are enclosed by a hard structure called the seed coat that protects the embryonic plant within. Some flowering plants, furthermore, have an extra layer called the pericarp, commonly known as fruit. Within the seed lies the embryonic plant, which contains small leaves and roots. What sets flowering plant seeds apart from the seeds of nonflowering plants is the endosperm, extra seed contents produced during fertilization that feed the embryo as it grows.
Seeds themselves represent a major evolutionary leap for the plant kingdom, being easily transportable and tough enough to withstand environmental stresses. Flowering plant seeds, however, are the most advanced seeds of all. By developing fruit, plants encourage hungry animals to transport their seeds for them. The endosperm of flowering plant seeds, which is lacking in nonflowering plant seeds, provides food for the developing embryo.