184 GUIDE TO THE STUDY OF LICHENS. 



medium, usually marginal, margin not raised. Disk 

 convex, reddish-brown. Spores colorless, four-celled, 

 oblong, elliptical, granular contents, 30yu X 7^. 



This rather rare and highly interesting lichen has 

 been found in the New England States and in Cali- 

 fornia. 



Jf.. Mallotium. 



The thallus of this genus indicates a higher develop- 

 ment than Leptogium ; it is thicker and larger ; it fre- 

 quently bears soralia or soredia ; its cortical tissues are 

 more highly developed. Color is dark-blue. The 

 lower surface bears numerous very long delicate rhi- 

 zoids. The algee are JVostoc. 



The apothecia are similar to those of Collema and 

 Leptogium. As a rule, the few representatives which 

 occur in the United States are found to be sterile. 



They occur upon trees and rocks, and range from 

 north to south, though they are quite rare. Generally 

 Mallotium is classed with Leptogium. As a genus it 

 requires further study. 



1. Mallotium saturninum. Thallus large, quite 

 thick, nearly monophyllous, margin lobate ; upper sur- 

 face granular, dull gray to dark-blue ; lower surface 

 bearing long, slender, grayish rhizoids. Apothecia not 



seen. 



IX. PANNARIACE^. 



Considerable uncertainty exists as to the limitations 

 of this family ; genera are included which seem to have 

 no possible genetic relationship to other genera {Ephehe, 

 Lichina). The algal-characters vary greatly, and have 

 been made the basis of the generic determination. The 



