160 A TEXT-BOOK OF BOTANY 



89. Lichens. Lichens are abundant everywhere, form- 

 ing splotches of various colors on tree trunks, rocks, old 



FIG. 154. A common lichen growing on bark; the numerous dark disks are lined 

 by a layer of asci. 



boards, etc., and growing also upon the ground (Figs. 154 

 and 155). They have a general greenish-gray color, but 

 brighter colors also may be observed. 



The great interest connected with lichens is that they 



155. A common foliose lichen growing upon a board. 



