LICHENS. 95 
tree; and yet it is with these small and ap- 
parently insignificant objects that nature shades 
the picture, balances and contrasts the colouring, 
clothes the nakedness, and softens down the 
irregularities and deformities of the whole scene, 
which would otherwise be stiff and hard as a 
forest-piece painted by a Chinese artist. 
Lichens are exceedingly diversified in their 
form, appearance, and texture. About five hun- 
dred different kinds have been found in Great 
Britain alone, while upwards of three thousand 
species have been discovered in different parts of 
the world by the zealous researches of naturalists. 
In their very simplest rudimentary forms, they 
consist apparently of nothing more than a collec- 
tion of powdery granules, so minute that the 
figure of each is scarcely distinguishable, and so 
dry and utterly destitute of organization that it is 
difficult to believe that any vitality exists in 
them. Some of these form ink-like stains on the 
smooth tops of posts and felled trees ; others are 
sprinkled like flower of brimstone or whiting over 
shady rocks and withered tufts of moss; while a 
third species is familiar to every one, as covering 
with a bright green incrustation the trunks and 
boughs of trees in the squares and suburbs of 
smoky towns, where the air is so impure as to 
forbid the growth of all other-vegetation. It also 
