GENERA AND SPECIES. 185 



characters of the thalhis also vary greatly ; the smaller 

 and more insignificant forms are fruticose ; the higher 

 forms are foliose. This seems to be contradictory to 

 the arrangement of the Parmeliacece, in which family 

 the fruticose forms are placed highest. Upon close 

 examination it is, however, very evident that the fruti- 

 cose forms of the Pannariacece are very lowly organ- 

 ized as lichens. 



The algae of this family are blue-green, with the ex- 

 ception of those of Psoroma and Sticta in which genera 

 they are bright-green. As regards spore-characters, 

 the only thing that can be stated here is that none are 

 multilocular and that th^y are not very large ; most of 

 them are colorless. The apothecial-characters are as 

 variable as the thallus-characters. 



KEY TO THE GENERA. 



Symbiotic algae {Sirosiphon) forming the 

 bulk of the thallus-structure of 

 minute brandling filaments , . 1. Ephehe. 

 Symbiotic algae (not Sirosiphon) not form- 

 ing the bulk of the thallus struc- 

 ture. 



Thallus crustose, dark 2. Lecofhecium. 



Thallus fruticose, dark, minute. 



Cortical tissue \v;vnting, spores simple. 



Algae in chains {Rivularia) . . . . 3. Lichina. 



Algae singly ( Gloeocapsa) 4. Omphalaria. 



Cortical tissue present, spores two- 

 celled, colorless 5. Polychidium. 



Thallus folio«e. 



Spores simple, colorless. 

 Apothecia innate in depression of 



thallus 6. Heppia. 



Apothecia discoid, sessile. 

 Algae singly, bright -green {Proto- 



coccus) 7. Psoroma. 



Algae in colonies, blue-green (Poly- 

 coccus) , . . . . S. Pannaria. 



