GENERA AND SPECIES. 175 



ness. Its color varies from gray to greenish-gray. 

 The algae are Protococcus. Soralia are quite common 

 and seem to attain a high development in this genus. 

 Darbishire, who has made a special study of the soralia 

 of the Pertusarias, is inclined to the view that they 

 are phylogenetically derived from apothecial structures. 



The apothecia are globose and immersed in warty 

 elevations of the thallus. Usually there is no percep- 

 tible pore-opening. Absence of any marked coloration 

 of the apothecia is characteristic. Spores are simple, 

 large, colorless, one or two in each spore-sac. The 

 inner spore-wall is reticulately marked in some species ; 

 oil-globules are often present. 



Most of species are cosmopolitan ; they occur upon 

 bark and rock, less commonly upon moss. 



1. Pertusaria pustulata. Thallus very deficient, 

 grayish. Apothecia entirely immersed in the substra- 

 tum, producing pustular elevations and finally opening 

 by a minute apical pore. Spores typical, but inner 

 wall not reticulate, 75/x, X 43/x. 



2. Pertusaria leioploca. Thallus deficient of scat- 

 tered apothecial warts, greenish-gray to yellowish- 

 brown. Apothecia wholly immersed in the warts. 

 Spores typical (nor reticulate), usually four to six in 

 each spore-sac, 60/m X 22/i. 



3. Pertusaria multipuncta. Thallus usually entire, 

 somewhat fissured, sometimes rugose or areolate, pale 

 ash-gray. Apothecia immersed in thalline warts, 

 single or confluent. Spores typical, inner spore- wall 

 reticulate, 15CV X 60/>t. 



Jf.. Pertusaria glohularis. Thallus thin, apothecial 



