GENERA AND SPECIES. 127 



3. Graphis. 



This gBDus is well represented in the southern 

 states. The thallus is always crustose, though it may 

 attain considerable thickness. The thallus, as well as 

 the apothecia, begins development below tlie surface 

 of the substratum, but soon breaks through after which 

 the thallus rapidly spreads. The algae are Chroolepus. 



The apothecia are distinctly linear, often branching, 

 bent or angular. The disk is black in the northern 

 species, black or white in the southern forms. The 

 color of the thallus also varies from greenish-gray to 

 white. The spores are comparatively large, six to 

 twelve-celled, colorless, somewhat curved ; the more or 

 less gelatinous exosporium is wavy in outline. 



The species occur upon trees, preferably the smoother 

 barks. 



1. Graphis elegans. Thallus hypophloeodal. Apo- 

 thecia linear, branching, prominent. Disk black. Usu- 

 ally sterile. 



This lichen closely resembles G. scripta and is, per- 

 haps, merely a varietal form of that species. 



2. Grapliis scripta. Thallus hypophloeodal. Apo- 

 thecia as in G. elegans, less prominent. Spores eight- 

 celled, colorless, variable in size, 34/x, X H/^* 



This lichen is common everywhere. 



3. Graphis dentritica. Thallus rarely becoming 

 epiphloeodal at maturity. Apothecia radially linear 

 and branching. Disk black. Spores colorless, usually 

 eight-celled, one end often narrowed, 24/x X 6.5/x. 



4' Graphis eulectra. Thallus soon becomes epi- 

 phloeodal, light-gray to nearly white, evenly spreading. 



