176 GUIDE TO THE STUDY OF LICHENS. 



warts united in groups of from two to six ; gray. Apo- 

 thecia entirely immersed, small pore often visible. 

 Spores typical but not reticulate, 95^ X 33/x. 



5. Pertusaria glomeridata. Thallus consists of 

 numerous confluent apothecial warts, nearly white to 

 gray. Apothecia immersed, opening by small pores. 

 Spores typical, inner wall reticulate, loO/x X 60/x. 



6. Pertusaria communis. Thallus thick, rugose 

 and somewhat fissured, gray. Apothecia in groups, 

 immersed in apothecial warts, apical pore present. 

 Spores typical, inner wall reticulate, 1 50/x X 47/*. 



This species, as well as other species of the genus, 

 were formerly included among the PseudoUchenes or 

 Lichenes imperfecti, under the name of Variolaria. 

 P. com. contains a large percentage of oxalate of lime 

 and had been used in France as the source of oxalic 

 acid. It was used as a remedy in feyers and as an 

 astringent in intestinal troubles. Many Pertusarias 

 were more or less recommended in the dyeing industries. 



1. Pertusaria velata. Thallus thick, areolate, light- 

 gray. Apothecial warts bearing apothecia which 

 open by apical pores showing the pale disk. Spores 

 yery large, typical, but not reticulate, 180/x, X 65/x. 



8. Dermatocarpon. 



The only representatiye of this genus which came to 

 notice is generally included in the genus Endocarpon. 



The thallus is yery minute for a foliose type. Care- 

 ful search with a pocket lens is necessary to detect it. 

 It consists of a single entire lobe closely adnate to the 

 substratum (rock) and is of a dark color. Several of 



