52 



POPULAR HISTORY OP LICHENS. 



absorbed from the soil ; in the latter, from the bark of the 

 fir and other trees on which the plant grew. We can 

 however approximate proof more closely, for it has been 

 found that iron is detected in many species growing on fer- 

 ruginous soils, and silica in those inhabiting quartzose rocks. 

 But the chemistry of the Lichens is in a very primitive and 

 unsatisfactory condition ; and, until it is more fully studied, 

 the question of the source or nature of their food cannot 

 be satisfactorily determined. 



Lichens are perennial ; they grow very slowly, but they 

 attain an extreme age. Some species, growing on the pri- 

 mitive rocks of the highest mountain -ranges in the world, 

 are estimated to have attained an age of at least a thousand 

 years ; and one author mentions, after the lapse of nearly 

 half a century, having observed the same specimen of Sticta 

 pulmonaria on the same spot of the same tree. If this be 

 the case, it is impossible to calculate how many ages we must 

 go back in memory to trace the origin of the lichenose coat- 

 ing, the grey and yellow "time-stains," of many a weather- 

 beaten battlement ; or to consider what deeds these venerable 

 crusts have witnessed — what changes they have outlived in 

 the past history of our country. The hoary Usneas, Eama- 

 linas, and Physcias of our forest-trees, like the grey beard 



