114 FIRST FORMS OF VEGETATION. 
the modes of reproduction increased. And what 
an admirable provision is this for the preservation 
of plants, which would otherwise be speedily exter- 
minated, exposed as they are to the contingen- 
cies of being successively scorched, drenched, and 
frozen on the same naked and barrenrocks! And 
how greatly does it exalt these humble plants in 
our estimation! Gifted with such powers of re- 
production as these, we can view the smallest 
lichen, not as a+ single phyton, not as a single 
frond, but as the aggregate of, it may be, thou- 
sands of these, view it occupying as much space, 
and exercising as great an influence in the eco- 
nomy of nature as the largest forest tree, and 
rivalling it even in longevity. 
Lichens are very slow-growing plants. They 
spring up somewhat rapidly during the first year 
or two, as is evinced by the luxurious growth 
which they form over young fruit-trees and 
espaliers in gardens; but after a circular frond is 
formed, they subside into a dormant state, in 
which they remain unaltered for many years. 
Mr. Berkeley says that he watched individuals 
for twenty-five years, which are now much in the 
same condition as they were when they first 
attracted his notice. Some of the grey rosettes 
of Parmelia which occur on walls and rocks, not 
unfrequently attaining a circumference of many 
