Lichen

Aiton's Encyclopedia (1910)

li'ken, a vegetable growth occurring on rocks, trees, and soils. Lichens are ordinarily of a dry, leathery texture, although some are gelatinous. They are gray, brown, greenish, yellow, blue, and even black. They have the form of crusts, patches, and cups. Sometimes they have a branching or even a moss-like growth. There are over 4,000 species. Many kinds grow best in an exceedingly dry situation; others like moisture. Most kinds prefer sunlight; others require shade. Nearly all lichens are able to endure long continued drouth without losing their vitality. They are surpassed only by bacteria in their ability to withstand the severity of Arctic winters. Lichens are found in all parts of the world. The Iceland moss, used for the table, and the reindeer moss, on which the herds of Lapland feed, are lichens. A lichen of Arabia is collected for food. When dry it is blown about by the winds and scattered in small grains or masses. It is just possible that the manna of the Wilderness, eaten by the Israelites, consisted of this lichen. The blue dye known as litmus is obtained from a lichen. One of the curious facts about lichens, and one that until lately escaped the attention of botanists, is that they are parasitic on lower forms of life known as algae. Strange as it may seem, the little green spot on the surface of a stone feeds on a still less conspicuous plant which it conceals and shelters. The surface of rock is dissolved or eaten by the chemical action of acids found in both lichens and algae, thus forwarding disintegration and the formation of soil. An attentive observer has stated that the rocks and tree trunks of New England are painted with lichens; while those of Old England are clothed with moss.