150 



PRACTICAL MICROSCOPY. 



upon rocks, stones, trees, old railings, twigs, bushes, heath, 

 moss, and in many other places. 



Lichens are mostly of large size, and require thin sections 

 to be cut ere the structures can be satisfactorily made out ; 

 but some should be always mounted as opaque objects, to 

 show what the natural form of the plant is. 



FIG. 136. 



FIG. 137. 



Fig. 1 36 shows a piece of fencing upon which is growing 

 Lecanora cerina, while the next illustration, Fig. 137, shows 

 Usnea barbata, one of the filamentous species. Among 

 the more familiar kinds are Parmelia parietina, Lecidea 



