Welcome to You Ask Andy

Earl Ownby, age 14, of Jackson, Miss., for his question:

What are lichens?

The lichen is a living proof that two heads are better than ones For actually it is two plants living together in profitable partnership. The bulk of the plant is a fungus. And a fungus plant is a mesh of pale threads. Its spongy body is splendid for holding moisture, more moisture than it needs. But its pallor means that it has no green chlorophyll. And green chlorophyll is the stuff plants use to make food from air, water and sunshine.

A fungus must have prefabricated plant food, food manufactured by other plants. Vile find mushrooms growing around ancient tree stumps, toadstools rooted in woody trunks. These fungus plants dine on the food manufactured by chlorophyll in the leaves of green plants. They tend to grow in the shade where the damp soil is rich with organic matter.

However, we find lichens growing in bleak, exposed places. Delicately toned rosettes adorn the faces of barren rocks. There are lichens high above the timberlines of tall mountains. And, when the sea recedes, lichens appear on the bare rocks soon after they become dry land. Lichens are everywhere. Some grow in steamy jungles and some, such as the reindeer moss, thrive under the deep winter snow.

The fungus part of the lichen can do this because it has a house guest, or more likely many house guests. The borders are tiny alga plants and they live in the rooms provided among the spongy fibers of the fungus.

The alga plants have color. They may be mauve, pink, yellow, brown grey or even black. But these tones merely mask the green color which is always present. For every algae, green or any other color, contains green chlorophyll. This means the algae can manufacture their own plant food from moisture, air and sunshine. In fact, they can make more food than they need.

Most of the algae are water dwellers. Those that live by themselves on land must live in moist places. For they cannot store water as the larger, more complex plants can. This is why they are quite willing to go into partnership with a spongy fungus plant.

The fungus plant provides shelter and moisture for the thirsty algae: The algae provide plant food for the hungry fungus. This kind of partnership is called symbiosis. It means living together on a mutual basis of give and take. The pretty little lichens are living examples of profitable symbiosis.

The symbiosis is handed along to the next generation. For the lichen practices symbiosis even in parenthood. At certain times granules of dust appear under the surface. Each little grain is composed of a few cells of an alga plant, a few cells of a fungus plant. They are called the soredia.

When ready, the soredia are blown away by the passing breezes. They drift and soar through the air and finally come to rest. Some of them will settle on a suitable rock, a fence, a tree trunk, an old wall or a patch of ground. The fungus cells will swell with the first dew. And soon we have a new generation of lichens.

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