THE STORY OF THE LICHENS 123 



statement that lichens are able to dissolve the 

 mineral elements from the rocks on which they 

 grow. Many of the crust lichens, for instance, 

 may frequently be found actually sunk into the 

 substance of the rock on which they are grow- 

 ing. In the course of untold ages one can 

 understand what a big part these humble 

 plants must have played in preparing the sur- 

 face of the earth for the more highly speciahsed 

 vegetation. 



In the foregoing descriptions of the vari- 

 ous kinds of lichens an endeavour has been 

 made to use only the simplest words and 

 phrases. This has been done in order to give 

 more graphic word pictures of the kinds 

 described. It should be clearly understood, 

 however, that such terms as stalk, leaf, root, 

 etc., can only be used in connection with lichens 

 in a very general sense. Properly speaking, the 

 spread-out portion of the lichen should be 

 spoken of as a tlialltts, whilst the stalk or 

 branch has not the distinctive character which 

 these parts have in an ordinary plant. The 

 little root-like processes on the under side of 

 the leafy lichens [Peltigera, for instance) are 

 more for the purpose of securing an attach- 



