MODE OP GROWTH OP LICHENS. 



are many species, which ordinarily grow upon the trunks of trees; 

 and these are commonly spoken of as Mosses, but incorrectly 

 so. The shaggy appearance of the apple-trees of an old Orchard 



FIG. 8. LICHENS. 



is in general entirely due to Lichens, although a few Mosses may 

 sometimes be found among these. Of such Lichens, by far the 

 greater part vegetate indifferently on all kinds of trees, and they 

 flourish equally well upon a damp wall ; so that there is no 

 reason to suppose that they derive any more nutriment from 

 the stems on which they grow, than is afforded by the moisture 

 covering their surface. There is no doubt, however, that some 

 trees are much more favourable to their growth than others. 

 Thus, the Beech, Elm, Sycamore, and Lime, are comparatively 

 seldom found infested with the common Beard-moss, which 

 clothes so profusely the Fir, Ash, Oak, or Birch ; so that the 

 poet's epithet of u rude and moss-grown beech" is by no means 

 appropriate. 



36. The fructification of the 

 Lichens is not much raised above 

 the general surface, but is usually 

 im' edded in certain parts of it, 

 somewhat differently formed from 

 the rest, and termed shields. The 

 early growth of these plants is 

 favoured by darkness ; but for the 

 ripening of the reproductive bodies, 

 a considerable quantity of light is 

 required. The development of the 

 shields, which takes place under its 



FIG. 9. PARMEMA PERFORATA 

 Lichen with projecting shields. 



