80 GUIDE TO THE STUDY OF LICHENS. 



II. NATURAL KEY TO THE FAMILIES. 



The natural keys to the genera are given after the 

 description of the families. In the use of the natural 

 key to the families and genera, the beginner is depend- 

 ent upon the use of the compound microscope. The 

 student is advised to keep in mind the suggestions 

 given in the chapter on " The Study of Lichens." 



KEY. 



Algae of the thallus bright-green. 

 Fungal type of apothecium. 



Apothecia terminal on stipes or on the f ruticose thallus. 

 Disk closed, finally opening by a terminal pore or 

 crevice /. CALJCIACEjE. 



Disk open, convex, light-brown or red, 



//, CLADONIACEjE. 



Apothecia sessile on the crustose or foliose thallus. 

 Disk cup-shaped, flattened or convex, brown or black, 



///. LECIDEACE^. 



Apothecia linear, irregular or stellate ; thallus crus- 

 tose IV. GRAPHIDACE^, 



Thalline type of apothecium or apothecia immersed in 

 the thallus. 

 Apothecia discoid and sessile, rarely immersed. 



Plasmic masses of spores united, spores two-celled, 



r. PHTSCIACEuE. 



Plasmic masses of spores not united, 



VI. PARMELIACE^. 



Apothecia immersed in the substratum or thallus, 



opening by a minute pore, VII. VERRUCARIACEM. 

 Algae of the thallus blue-green.^ 



Thallus foliose, dark-blue, gelatinous when moist, 



VIII. COLLEMACEJS. 



Thallus minutely fruticose or foliose, not gelatinous when 



moist IX. PANNARIACEjE. 



The descriptions of the families and genera will be 

 made as brief as possible. Those who wish to study 



1 The following genera of the Pannariaceae ha.ve bright-green algse; 

 Nephroma, Solorina, Sticta and Psoroma, 



