David Jacobi, age 12, of Santa Rosa, Calif., for his question:
HOW DO SEEDS DEVELOP?
Most plants depend upon seeds alone to continue their kind. The part of a plant's flower which contains the tiny seed eggs is the ovary. To develop into healthy seeds, the eggs must receive pollen from the same flower or the same kind of flower.
All seeds are either "gymnosperms" or "angiosperms.11
Gymnosperms are naked seeds, not enclosed in an ovary. They include those of the pine and all other cone bearing trees as well as certain fernlike plants of the tropics.
Angiosperms are enveloped seeds which enclose an ovary and which ripen as a pod or fleshy fruit. The seeds of all plants, trees, shrubs and herbs that bear flowers are angiosperms.
In order to germinate yr sprout, a seed must have air, moisture and the right temperature after it has been pollinated and ripened.
When a seed is planted, it swells with moisture. As the embryo begins to grow, it bursts its seed coat. The root tip pushes through. The embryo stem doesn't lengthen until it has rootlets to anchor it firmly in the earth. It then arches up through the earth's crust and brings a delicate plant bud into the air.
As the stem strengthens, the bud is exposed to the light and air it needs for growth. And so a seed has developed into a plant.
The size of seeds vary almost as much as the different kinds of seeds. Tobacco seeds, as an example, are so tiny that one seed pod may contain as many as 40,000 seeds. Poppy seeds are only slightly larger.
On the other end of the size scale is the coconut. One kind produces a single seed that weighs about 22 pounds.
Seeds also come in many different shapes and colors. Some are smooth while others have ridges. Some are dull in color while others are bright.
Nearly all seeds thrive best if they are planted less than a year after they have ripened. But most of them will keep for some time. Two year old corn germinates readily, but if corn is kept for three or four years, its chances of sprouting are less.
Some beans may sprout if they are eight years old, but usually a bean embryo dies after the third year. Cucumber seeds may be kept for as long as 10 years while wheat has been known to germinate and grow after 30 years.
Nature's work is not finished when seeds have ripened. They must have a chance to sprout and grow. If they fell straight to the ground, beneath the plant that bore them, they would be too crowded to thrive. The seeds must be scattered and nature has a way of doing this.
Birds are creatures that are attracted to the bright color of ripe fruit. The seeds they swallow are not digested. They pass through the birds' bodies and are scattered in this way.
Wind scatters many seeds. Some have parachute like tips that let them float great distances while others have wing like or propeller like arms that let them fly with the wind. Hooks and barbs on some seeds make it possible for them to cling to the fur of passing animals. Some plants have seed pots that explode when dry, scattering seeds great distances.