FLORA OF THE MOUNTAIN. 259 



ter where they give way to fungi ; but they often occupy 

 the surface of living plants, especially their bark. In the 

 tropics they lay hold of evergreen leaves. Their chosen 

 climate is one that is temperate and moist ; aspects to the 

 north or west are also their favorite resort, for they shun 

 the rays of the noon-day sun. No place seems to be a more 

 constant haunt than the surface of sandstone rocks, and 

 buildings in cool and moist countries. They are met with, in 

 one place or other, from the equator to the pole, and from the 

 sea-shore to the limits of eternal snow. The finest species 

 are found near the equator; the most imperfect, such as the 

 crustaceous genera, which can hardly be distinguished from 

 the rocks they grow upon, are chiefly observed on mountain- 

 tops, and near the pole. The Idiothalami are most abund- 

 ant in tropical America." 



The Lichen appears, then, the pioneer of that splendid 

 world of forms which seems, from its entire dissimilarity of 

 structure, to ignore its affinity or alliance by any conceivable 

 nexus with it, and as the first blundering effort of inorganic 

 matter to enter the higher sphere of life. The mountain's 

 rocks and forests present an extensive field of research in 

 this department of botany, from the same causes which give 

 exuberance of growth to the other orders of cryptogamic 

 plants. From the lower varieties of pulverulent and crus- 

 taceous lichens covering stones, fences, and walls, with white, 

 gray, or yellow scurf, to the more complex structures of 

 fronds, they are found picturing the surfaces of all fixed ob- 

 jects with every conceivable shape of spots and markings, 

 clinging to the bark of trees, investing their branches with 

 fantastic scales and gelatinous skins, or floating festoons of 

 hair ; destitute of roots, but eroding at last the hardest 

 vitreous slags. Drawing their nourishment from the air, 

 they adhere to the naked surfaces of everything, clothing the 

 rock and tree with an endless variety of dress and orna- 

 ment. 



In the class of uses, the order abounds in valuable ele- 

 ments, nutritive, medicinal, and chemical coloring-principles. 



