150 J6otani2 



The carbon, oxygen, ammonia, hydrogen, in air and 

 rain, afford them their nourishment. The lichen 

 generally refuses to grow in foul air laden with 

 noxious gases. In the impure air of cities few 

 ai)pear, but they abound in the open country. They 

 absorb by all the surface except the base by which 

 they are fastened to their place of dwelling. They 

 have no roots, and simply adhere to bare Kocks, 

 sapless wood, even to naked glass, from which they 

 can receive no nutriment whatever. 



In comparison with what is known of plants in 

 general, our knowledge of lichens is yet ver}^ limited. 

 They seem to be made chiefl}^ of a kind of gelatin, 

 which exists in lichens only. Humble as they ap- 

 pear, they have always been of large importance in 

 arts and manufactures. They j^roduce exquisite 

 dyes — a rich, costly j^urple, a valuable scarlet, many 

 shades of brown, and particularly splendid hues of 

 blue and yellow are obtained from these common 

 little growths, which in themselves display chiefly 

 shades of black, gray and green, varied with pink, 

 red and orange cups, balls and edges. 



Formerly the gelatin of lichens was used as a sub- 

 stitute for gum-arabic ; now other substances have 

 taken its place in commerce. Once it was employed 

 as a basis for perfumes and toilet powders ; in this 

 direction also it is out of fashion. 



