Fred Sempek, age 10, of Springfield, I11., for his question:
HOW DOES NATURE PLANT SEEDS?
Nature has many different ways to give ripened plant seeds chances to sprout and grow. If they simply fell straight to the ground, under the plant that bore them, they would be too crowded to thrive. The seeds must be scattered or dispersed.
When the seeds of some fleshy fruits are ripe, ready for planting, the skin of the fruit turns a bright color or even black or white to make it easy to see against the green leaves. Birds and other creatures are quickly attracted and eat the fruit.
The seeds of the fruit that is eaten are not digested. They pass through the animal's body and are scattered in this way.
When dandelion seeds are ready for planting, each seed has a long tail tipped with a cap of fluffy hairs. The wind carries the seeds off in many directions.
Milkweed, cotton, kapok and other seeds are covered with fluffy down which lets them sail on the wind. The clematis seed trails a long feathery plume for the same purpose.
Other wind born seeds have graceful wings instead of down. The most familiar wings are probably those of the maple seeds which grow in pairs. The pine, too, has seeds with wings. Their wings are curved like a propeller blade which helps the seeds spin in the air and catch air currents from all directions. Ash, elm and other trees also have seeds with wings.
Many seeds that grow in pods are too heavy for the wind to scatter. Some pods actually shoot out their seeds, forcing them to hop far away by an elastic contraction of the inner wall of the pod. When a bean pod dries and splits into halves, it whirls the beans out in many directions by twisting or curling.
Some seeds travel far from the parent plant by means of hooks and barbs. These grasp and cling to the fur of passing animals. Burs, stick tights and Spanish needles are well known, for they cling to the clothes of people who brush against them.
Tumbleweeds on the plains roll themselves into balls when the seeds are ripe and then the roots dry and shrink. The first wind uproots the entire plant and sends it rolling over the prairies, scattering seeds as it goes.
Many plants produce huge numbers of seeds because not all that are scattered become plants. Many fall where conditions are not suitable for germination and growth. Many are eaten by birds and rodents. In many the embryo is not alive.
Some plants and flowers will produce thousands of seeds. Even though so large a quantity is produced, the number of them that will sprout is very small.
On the other hand, some plants and trees only produce a few seeds. A coconut palm, for example, might only produce 20 seeds each season. Whenever there is a small number of seeds, very few can afford to be wasted.