THE LICHEN TRIBE. 283 



is yellow, brown or green, the texture of the ex- 

 pansion leafy, and the margin cut up into many 

 lobes ; these are the most nearly related to leafy and 

 more perfect plants (Plate XXV. \. fig- 1. & 2.) ; in 

 others the expansion is merely a thin crust, which 

 readily crumbles in pieces, the species having scarcely 

 vital energy enough to keep the cells of which they 

 are composed in a state of cohesion. Such plants as 

 these are called Lichens. They arc found chiefly in 

 the temperate or colder regions of the earth. Some 

 of them (Gyrophoras) crawl upon the surface of the 

 earth, spreading their dingy, cold, and damp bodies 

 over whole plains in the desolate regions of the 

 north ; others (Usneas, Ramalinas, &c.) spring up 

 on the branches of trees, and hang Aowa from 

 them like grey and netted beards, giving the unfor- 

 tunate plants of which they take possession, a hoary 

 wintrj' aspect even in the summer ; some (Parmelias, 

 Lecideas, &c.) overrun old walls, stones, and rocks, to 

 which they communicate those mild and agreeable 

 tints, which render ancient ruins so peculiarly pleas- 

 ing to the eye; and finally a fourth description of 

 Lichens (Opegraphas) establish themselves upon the 

 bark of living trees, occasionally burying themselves 

 beneath the skin, through which their shields alone 

 peep forth in the strange form of the letters of some 

 eastern tongue. 



Plants of this tribe have no parts in the smallest 

 degree resembling flowers ; they have no certain 

 mode of multiplying themselves except by the dis- 

 persion of little spores, which are nothing but ex- 



