How Does a Seed Become a Flower?

Flowers, the reproductive organs of a plant, are often the final stage in the plant's life cycle.

The process that leads a plant from its seed, to the production of flowers--the organs by which the new plant will itself reproduce--is long, usually the length of a season, and contains several steps. Through these steps the plant anchors itself, gains access to water, sprouts leaves for the production of food, and finally grows flowers, ready to begin the process again with a new plant.

The Taproot

The first plant part to crack the surface of the seed is called the taproot. Through a combination of cell replication and cell elongation, the taproot grows down into the soil, looking for water and firmly anchoring the new plant. As it reaches water, the taproot splits into several branches, bolstering the plant's foundation and increasing its access to moisture.

The Stem

Once the taproot has begun delivering water to the seed, a second process of replication and elongation sends the plant's new stem up through the surface of the soil in search of light. The process of taproot and stem growth uses up most of the store of food initially present in the seed's endosperm, so it's at this point that the plant must begin generating its own food.

The Leaves

The stem, doing its own branching-out above ground, uses the last of the nutrients in the endosperm to grow leaves, the cells of which come equipped with a chemical called chlorophyll that allows the leaves to transform solar energy (the light of the sun) into chemical energy (sugars and carbohydrates for the plant). Once a few leaves are in place, the plant can start using the energy they collect to produce more, and the endosperm's initial supply of carbohydrates is abandoned.

Timing

Once the leaves are in place, the plant has everything it needs to survive--but to reproduce, it must grow flowers. When exactly this happens depends on what kind of plant it is. Annuals, like snapdragons, produce flowers at the very end of their life cycle (usually at the end of the year or season), just before dying. Biennials, like parsley, also die after flowering, but they wait through two seasons, going dormant during the colder months. And perennials, like dahlias (and, technically, trees), flower at particular times during the year, over and over again. The plant can't actually measure time to determine what part of the season it is, but it can detect changes in temperature and day length. Artificially inducing such changes in greenhouses allows botanists to manipulate plant flowering.

Growth

When a plant is ready to flower, the part of a stem that would normally continue to grow or sprout leaves is converted to a "floral meristem," and the different parts of the tip of the stem begin to transform into the different parts of the flower. These parts include the sepals at the base of the flower, the recognizable petals at the top; the stamen, or male reproductive organ; and the pistil, or female reproductive organ. Flowers are hermaphroditic, and rely on wind and pollinating animals like bees to carry the pollen of a stamen to the eggs of another flower's pistil, starting the reproductive process that will end in a new seed, ready to grow a new plant.

References

• Teachers' Domain: From Seed to Flower
• Kimball, John W.: Flowering