THE PAGE OF NATURE. 75 



admirable provision is this for the preservation of plants, 

 which would otherwise be speedily exterminated, exposed 

 as they are to the contingencies of being successively 

 scorched, drenched, and frozen on the same naked and 

 barren rocks. And how greatly does it exalt these 

 humble plants in our estimation ! Gifted with such 

 powers of reproduction 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, thousands of these,' 

 view it occupying as much space, and exercising as great 

 an influence in the economy 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 j 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 con- 

 dition 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 circumfer- 

 ence of many feet, must be very aged, judging by this 

 standard. The foliaceous and shrubby species are the 

 most fugacious, though even these have great powers of 

 longevity. We have no data from which to ascertain 

 the age of tartareous species, which adhere almost in- 

 separably to stones. Some of them are probably as old 

 as any living organisms that exist on earth. The geo- 

 graphical lichen, which often spreads over the whole 



