GENERAL CHARACTERS OF BRITISH LICHENS. 



53 



of an old man, silently but eloquently proclaim Time's 

 ravages, and illustrate the constant succession of life upon 

 death, growth upon decay, which is going on around us. 

 "We have alluded to the age of the individual ; we shall 

 find no less interest in regarding the geologic age of the 

 family. Unger, in his ' Palseo-phytology/ mentions Lichens 

 among the few cryptogenic plants which have been de- 

 tected in a fossil state in the lower or earlier palaeozoic strata. 

 From the cellular character of the lower cryptogamic plants, 

 comparatively few have been preserved to us as fossils. 

 Their presence at so early a period of our earth's history 

 leads to reflection on the condition of lichenose vegetation 

 on our globe at the period w 7 hen the strata which now con- 

 tain their remains were originally deposited. It is not in- 

 consistent with analogy to believe — as in the case of an 

 allied family, the Ferns — that the stunted Lichens of our 

 w r alls or trees are but puny types of a once comparatively 

 gorgeous vegetation, whose nearest living analogues are the 

 large and showy foliaceous species of tropical forests. 



We have already alluded to the protean nature of the 

 Lichen-thallus and the frequency of its abnormal conditions. 

 This is perhaps the most appropriate place to review the 

 causes productive of its infinite alterations and metamor- 



