96 THE HISTORY OF CREATION. 



the former, and upon the nutritive substances prepared by it. 

 The green cells, containing chlorophyll (gonidia), which are 

 found in every lichen, belong to the Alga. But the colourless 

 threads (hyphfe) which, densely interwoven, form the princi- 

 pal mass of the body of Lichens, belong to the parasitic 

 Fungus. But in all cases the two forms of plants — Fungus 

 and AJga — which are always considered as members of two 

 quite distinct provinces of the vegetable kingdom, are so 

 firmly united, and so thoroughly interwoven, that nearly 

 every one looks upon a Lichen as a single organism. 



Most Lichens form small, more or less formless or irregu- 

 larly indented, crust-like coverings to stones, bark of trees, 

 etc. Their colour varies through all possible tints, from the 

 purest white to yellow, red, gi'een, brown, and the deepest 

 black. 



Many lichens are important in the economy of nature from 

 the fact that they can settle in the driest and most barren 

 localities, especially on naked rocks upon which no other 

 plant can live. The hard black lava, which covers many 

 square miles of gi'ound in volcanic regions, and which 

 for centuries fi-equently presents the most determined 

 opposition to the life of every kind of vegetation, is always 

 first occupied by Lichens. It is the white or grey Lichens 

 (Stereocaulon) which, in the most desolate and barren fields 

 of lava, always begin to prepare the naked rocky ground 

 for cultivation, and conquer it for subsequent higher 

 vegetation. Their decaying bodies form the first mould in 

 which mosses, ferns, and flowering plants can afterwards 

 take firm root. Hardy Lichens are also less affected by 

 the severity of climate than any other plants. Hence the 

 naked rocks, even in the highest mountains — ^for the most 



