Flowers are grouped depending on the length of time it takes to complete their life cycles. Tomatoes, marigolds and other annuals have a one-year cycle, then die during frost. Biennials such as carrots and foxgloves bloom only in their second year before they self-seed and die. Perennials often shrivel down in winter but bloom again each spring. Roses and daisies are perennials, as are many bulb plants like tulips and daffodils.
The Flower
Flowers are fed by nutrients and water traveling up the stem, and sugars produced in leaves during photosynthesis. Petals are often brightly colored to attract pollinators. In the center of the flower are the male stamens, each with a pollen-producing anther and a filament. The female parts of the flower are called carpels, each with a stigma, style and ovary.
Pollination and Fertilization
Pollen sticks easily to bees, hummingbirds, moths and other pollinators. While the animals travel in search of nectar and pollen for food, they often bump against a flower's stigma and deposit pollen carried from another plant. Wind can also transport pollen. When the male and female parts of a flower ripen together, a flower can self-pollinate.
The male pollen grains send out tubes that move down the female stigma, through the style and into the ovary, where each can pierce the nucleus of a single egg. The flower fertilization process is somewhat similar to human reproduction.
The Seed
A flower's fertilized eggs become seeds, while its ovary wall becomes the fruit that contains them. Rose hips are one example. Each seed is surrounded by a tough, protective coating containing food for the growing plant. A layer called the endosperm stores short-term nutrients, while the long-term supply is stored in two cotyledons that may resemble lima beans in shape.
Seed Dispersal
Seed dispersal serves several important functions: It limits overcrowding, helps seeds spread out into new areas and eases competition between the seeds and parent plant. Animals help with dispersal when they eat flowers or fruit and later excrete the seeds in their waste. Wind and water can also carry seeds away. Some plants "self-disperse," for instance, bursting in the hot sun to shoot the seeds in all directions.
Growth
Once a seed finds favorable conditions it begins to germinate or grow. The future root extends downward into the soil while the future shoot reaches upward for sunlight. Leaves form and begin to carry out photosynthesis while roots absorb necessary water and minerals.
Photosynthesis allows a plant to convert light energy into food stored as sugar. All that is required for this process is light, carbon dioxide and water. Veins in the leaves help transport water and nutrients throughout the plant as needed.
Finally, buds form to protect the developing flowers. Mature flowers unravel, complete with petals and the male and female reproductive organs. Pollen is produced, and the life cycle begins anew.
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