USES OF LICHENS. 



79 



and contribute to the increase of the vegetable soil, which 

 is next taken possession of by mosses and ferns, and gradu- 

 ally by various phanerogamic plants, shrubs, and trees : 



" They fall successive and successive rise ; 

 So generations in their course decay, 

 So flourish these when those are pass'd away." 



One of Nature's truest poets, Crabbe, describes this alter- 

 nation of life and death, birth and decay, in the gradual 

 development of vegetation, so well, that we cannot here re- 

 frain from introducing it : 



" Seeds, to our eyes invisible, will fiud 

 On the rude rock the bed that fits their kind. 

 There, in the rugged soil, they safely dwell 

 Till showers and snows the subtle atoms swell 

 And spread the enduring foliage : then we trace 

 The freckled flower upon the flinty base : 

 These all increase, till, in united years, 

 The stony tower as grey with age appears 

 With coats of vegetation thinly spread, 

 Coat above coat, the living on the dead : 

 These then dissolve to dust and make a way 

 For bolder foliage, nursed by their decay : 

 The long- enduring ferns in time will all 

 Die and depose their dust upon the wall, 

 Where the wing'd seed may rest till many a flower 

 Shows Flora's triumph o'er the falling tower." 



Travellers agree in describing Lichens as the first plants to 



