i 4 9 



The characters of the apothecia are also very variable. As in 

 the preceding groups these begin their development below the sub- 

 stratum ; some time before maturity they break through the surface ; 

 very rarely they remain covered over by a thin layer of the thallus 

 and remnants of the substratum ; they are small, usually irregular in 

 outline, never exactly linear, nor do they become markedly orbicu- 

 lar. The margin is irregular in outline, and frequently stellate ; 

 sometimes there is also a tendency to become linear, usually asso- 

 ciated with radiating projections. The hypothecium is usually more 

 or less dark colored, likewise the epithecium and the upper ends of 

 the somewhat granular simple paraphyses ; the epithecium rarely 

 becomes reddish brown. 



The spores are characteristic. They are oblong, either colored 

 or colorless, quite constantly four-celled, the ends rounded and one 

 of them narrowed, so that the general outline of the spore resem- 

 bles that of the sole of a shoe. 



The Arthonias are southern in their range, though less so than 

 Gracilis ; they occur mostly upon trees, less commonly upon decay- 

 ing wood. 



PLATE 31. 

 Arthonia radiata Ach. 



1. Natural size. 



2. Portion magnified. 



3. Arthonia fiunctiformis (nat. size) upon bark of tree; a, apothecia. 



4. Section of apothecium. 



5. Section of thallus. 



6. Paraphyses and spore-sac. 



7. Spores. 

 S. Algae. 



6. Mycoporum Nyl. Lich. Scand. 291. 1861. 



This lowly organized group of lichens is evidently related to the 

 'Graphidaceae, though authors do not agree on this point. The only 

 typical representative occurring in the territory is M. -pycnocarfum, 

 "upon the examination of which the following generic description is 

 based. 



The thallus is quite rudimentary and although beginning its de- 

 velopment below the substratum soon extends over its surface, form- 

 ing a very deficient crustaceous layer. The algae are quite numer- 



