THE STORY OF THE LICHENS 121 



may sometimes be found with fructifications, 

 although it is very often covered with the tiny 

 brood bodies, which appear like so much grey 

 powder on the growth. 



One of the most handsome of the leaf-like 

 lichens is Physcia parietina. This occurs very 

 extensively on the roofs of houses, walls, rocks, 

 and even on old hawthorn bushes. On flat sur- 

 faces it grows in a more or less circular patch, 

 and its bright yellow colouring makes the 

 plant a very distinctive feature. Years ago, 

 and quite likely in some parts of the world at 

 the present time, this lichen was largely used 

 for the dyeing of cloth. It seems that the drier 

 the situation the more brilliant is the tinting, 

 for examples found in damp and shady spots 

 are frequently of a less striking colour, and 

 on occasion are quite green. The plant is 

 often covered with spore-bearing cups which, 

 on account of their orange colouring, add very 

 much to the appearance of the growth. 



The third group into which the lichens may 

 be divided are those which form crusts on 

 objects in such a way that they cannot well be 

 removed without injury to the plant. The 



most abundant forms of these lichens are the 



Q 



