THE FLOWBRLESS PLANTS. 217 



leaves without branches, and without any distinct or 

 regular outlines, and found mostly on rocks. Others 

 are erect and ramified like trees and shrubs, but without 

 any thing that represents foliage. Such is that com- 

 mon grey lichen (Cenomyce) that covers our barren 

 hills, which is a perfect hygrometer, crumbling under 

 the feet in dry weather, and yielding to the step like 

 velvet, whenever the air contains moisture. In similar 

 places, and growing along with it, is found one of the 

 hepatic mosses, that produces those little tubercles — the 

 fructification of the plant — resembling dots of sealing- 

 wax, and eagerly sought by artists who manufacture- 

 designs in moss. But the most beautiful lichens are 

 those which are pendant from the branches of trees,. 

 (Usnea,) consisting of branching threads, of an ash- 

 green color, and bearing little circular shields at their 

 extremities. These lichens give character to moist 

 woods and low cedar swamps, where they hang like 

 funereal drapery from the boughs and deepen the gloom, 

 of their solitudes. 



Lichens, though inhabiting all parts of the earth, are 

 particularly luxuriant in cold climates, thriving in ex- 

 treme polar latitudes, where not another plant can live- 

 Nature seems to have designed them as an instrument 

 for preparing every barren spot with the means of sus- 

 taining the more valuable plants. Not only do they 

 cause a gradual accumulation of soil by their decay,, 

 but they actually feed upon the rocks by means of 

 oxalic acid that exudes from their substance. By this 

 process the surface of the solid rock is changed into ai 

 soil fitted for the nutrition of plants. After the lichens 

 have perished, the mosses and ferns take root in the soil 

 that is furnished by their decay. One vegetable tribe 

 after another grows to perfection and perishes, but to. 



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