. Practical botany. Botany. 238 PRACTICAL BOTANY home of small crustaceous lichens. As these grow, die, and decay, and are replaced by others of their kind, the living and decaying bodies tend to disorganize the rock. Weathering processes also assist in crumbling the rock, and after a time there is soil enough to permit the growth of other lichens and mosses and finally of larger plants. These pioneer plants are eventually driven from the rock by others that can live in the meager soil that is pro- duced by the li- chens and mosses. Certain kinds of crustaceous lichens are looked upon as the f
. Practical botany. Botany. 238 PRACTICAL BOTANY home of small crustaceous lichens. As these grow, die, and decay, and are replaced by others of their kind, the living and decaying bodies tend to disorganize the rock. Weathering processes also assist in crumbling the rock, and after a time there is soil enough to permit the growth of other lichens and mosses and finally of larger plants. These pioneer plants are eventually driven from the rock by others that can live in the meager soil that is pro- duced by the li- chens and mosses. Certain kinds of crustaceous lichens are looked upon as the forerunners of higher vegeta- tion in rocky re- gions which are too bare to per- mit other forms of vegetation to live. They are almost universally distributed over the earth. The time required for the production of soil sufficient for the growth of other plants depends largely upon the nature of the rock and upon the climate. Upon some lava beds it is said^ that after almost two hundred years I'rom their formation crusta- ceous lichens in places are still the only plants to be found. Lichens as food for herbivorous animals are of considerable importance in regions where other foods are scanty or where for parts of the year cold and snow render otlier vegetation 1 Warming, CEcology of Plants, chap. ! A cup lichen (Cladonia) This lichen often appears on moist ground, and at times forms the cup-like reproductive hodies, even sometimes having some of these form upon other cups. Two and one-half times natural size. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Bergen, Joseph Y. (Joseph Young), 1851-1917; Caldwell, Otis William, 1869- joint author. Boston, New York [etc. ] Ginn and company
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