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 (hyphz) 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 Alga—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, erust-like coverings to stones, bark of trees, 
ete. Their colour varies through all possible tints, from the 
purest white to yellow, red, green, 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 ground in volcanic regions, and which 
for centuries frequently 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 
