The How and Why Library/Life/Plants-Section III
III. Sailor Plants and Robinson Crusoes
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The first little plants were sailors. As they floated about in the water, the living drop of jelly or protoplasm, soaked food through the thin walls of the cells. One cell budded from another, and broke away to start a new family, or clung to the parent cells in a bead-like string, or in a knot that floated together. Then they budded all around the sides and formed mats and flat net-works of cells, held together by a gelatine in the cell walls.
Some of these nets and mats floated on rocks, in quiet places where the motion of the water was not strong enough to float them off again. As the rocks sheltered them, the plants were not so easily torn apart. The cells that lay on the rocks could not gather so much food, so they learned to cling. The free, floating cells gathered food, and budded and spread into feathery, leaf-like fronds. The plants lived in a colony, you see. So, by and by, they divided the labor just as people do in a village. It was the business of some plants, or cells, to cling to the rocks. Others waved in the water and gathered food. It wasn't necessary, any longer, and there wasn't room, for each cell to bud, although it could have done so. Certain cells began to collect budding material, in little raised dots on the fronds. When these dots ripened they were washed off. These bud dots were spores. They were not seeds, they were just the hints of seeds; and the cells that clung to the rocks were hints of roots; and the cells that spread out and floated were hints of leaves. All together they formed—seaweeds! Seaweeds belong to a family called algae. Algae are higher plants than fungi. But these colonies of cells did not deserve to go into a higher class until something else happened.
Some of these plants were born near the surface of the water where there was more air and sunlight. The sunlight turned them green. A green plant can take raw material like earth, air and water and, with the aid of sunlight, make its own food. Algae are found in oceans, rivers, lakes, ponds, marshes and warm springs, everywhere. Some of them are very beautiful, in a great variety of forms and colors. The very commonest algae that you can all find, almost everywhere, is the green scum that forms on quiet ponds and swamps. Scum is all broken up into single plants, or knots andstrings of cells, and can be easily separated and studied under a microscope.
There were some seaweeds that did not have a chance to become green. They grew far down in the deep sea, under tons of dark, almost airless water. They lay on rocks, flat and motionless and sluggish. They grew slowly but were hard to kill. They learned to live in colonies, to cling, to spread, and to grow spore buds, so they were a little above the fungi. By and by they were lifted, with the rocks they grew on. You know earthquakes lift the ocean floor. Parts of the deep ocean floor have been lifted suddenly into rocky islands. When that happened these colorless seaweed colonies were lifted, too, and shipwrecked in the air. They were just like Robinson Crusoe.
They wanted to live. If you were lost in the woods you would hunt roots and berries and nuts. You would strike stones together to make a spark and start a fire. You would make a bed of leaves in a cave. You would do your very best to live, wouldn't you? Robinson Crusoe was lost on an island a long time. He had to do many things he had never done before, and he changed so much that his best friends wouldn't have known him. If those deep-water seaweeds had been lifted slowly, to the air and sunlight, but still kept under the water, they would have become green algae. But they were castaways on the land before they got far enough along to be algae.
Most of them, millions and billions of them died. But those that died, decayed, mixed with the sand or rock waste and made the first soil that covered the bare rocks. Some of the water weeds managed to live by clinging to the rocks and decaying plants. But, like Robinson Crusoe, they had to learn new ways of living, and they grew to be very different from the algae, their water cousins, and different from the fungi, their ancestors.
For one thing, they became very dry and gray. They spread in broad scales to turn as many cells as possible to the air and rain. But they never turned green. You may find such plants today, on the rocks of the highest mountains, under the snows of cold countries, where grass will not grow, on dead or dying trees and fence rails, and on old house shingles. And, scientists tell us, they are to be found on the deepest rocks in the sea. They are called lichens, (li'kens). Some people think lichens are dry mosses, but they are not. They are plants between the fungi of the yeast andmildew, and the green algae of seaweeds. They are shipwrecked sailors, who learned a new way of life through many hardships.
Like the fungi, lichens live on other plants. They cannot get their own living. But, like the algae, they have learned to cling, to spread into leaf-like fronds, and to form spores or bud cells. In them is a hint of coming roots and leaves and seeds. They are often beautiful and are always curious. They are generally flat, dry, crinkly-edged scales, colored gray or silver or black. Sometimes, on old tree trunks, they are in thick, fluted ridges, and colored yellow or bright orange or white. With a microscope you can see that the gray scales are powdered with dusty round dots. Those are the spores or bud cells. When ripe the wind blows them, or the rain washes them away.
There is another thing the lichen has learned. Unable to turn green and so make its own food, it often goes into partnership with its higher born water cousin, the algae. It does it in this way. The lichen is made up of a network of thread-like cells. Each mash holds a little water. Algae spores, floating in the air and looking for water to grow in, find enough for just one cell, perhaps, in each mesh of the lichen. So they promptly move in. Often there are so many algae plants on the gray net surface of a lichen, that they turn it to a soft sage green color, very bright and moist. The algae being green, collect food from the sun and air and feed the lichen, and the lichen covers the algae with a network of gray thread cells to keep it from getting too dry.
Nature makes many partnerships between plants and animals that can help each other. Bees and butterflies help the flowers grow seeds. Men help plants to grow, and make friends of horses and dogs. Isn't it wonderful that, as low in the scale of life as algae and lichens, we should find this water plant and its shipwrecked cousin helping each other? (See Algae, Lichen, Chlorophyceae, Chlorophyll.)