LICHENS. 91 



CHAPTER VIII. 



LICHENS. 



THE Lichens are found growing upon the bark of 

 trees, old palings, &c. Those most easily seen 

 with the naked eye form grey or coloured dryish 

 patches or pendulous tufts; while the smaller ones 

 are singly easily overlooked, from their minute size 

 and close adhesion to the matrix or hody upon which 

 they grow, forming, by their aggregation, the grey or 

 otherwise-coloured dry and brittle coatings of almost 

 every tree or decaying branch. 



The Lichens derive their nourishment from the air, 

 and not from the matrix in this respect differing 

 from the Fungi, with some of which, as we shall pre- 

 sently see, they agree in the structure of the fruit. 



The structure of the Lichens is simple, no distinc- 

 tion of root, stem, and leaves existing in them, although 

 certain dry root-like fibres exist in many of them, by 

 which the plant is fixed to the matrix. The whole 

 consists mainly of a frond or thal'lus (0a\\o$, a leaf) . 

 This is either raised above the surface of the matrix 

 in a shrubby form, or spread upon the surface as a 

 flexible lobed layer (PL II. fig. 2), or it is dry and 

 brittle (crustaceous) and closely adherent (PI. II. 

 fig. 26), 



The fructification consists of little saucers, disks, or 

 streak-like furrows, often of a different colour from 

 the thallus, the structure of which will be best illus- 

 trated by reference to a few common species. 



PARMELIA'CE^E. Parmelia parietina (PL II. fig. 2) 

 is a very common Lichen, found on the bark of trees, 

 on old palings, &c. It is of an orange-yellow colour, 



