162 



are numerous and differ little from the medullary hyphae or not at all. 

 The prevailing color of the upper surface is gray, the medullary 

 layer is white, as is also the lower surface. The algae, which are 

 doubtless Cystococcus humicola, often occur in clusters of from four 

 to as many as twelve, enclosed by a common membrane, but solitary 

 forms are also common, in which respect they differ from the majority 

 of Cystococci occurring in lichens. 



The apothecia are quite small and occur immersed in the thallus ; 

 there is usually one in each areole ; rarely two or three, the disk 

 is markedly concave, the excipular margin never extending above 

 the surface of the thallus; sometimes the excipular margin is con- 

 stricted, thus forming a more or less complete perithecium, which is 

 dark, and the hypothecium is also more or less dark colored, but 

 never distinctly black. The paraphyses are rather long and slender 

 and somewhat granular. The spore-sacs are cylindrical, with the 

 spores usually in a single row. 



The spores remain colorless until they are fully formed ; in fact 



the immature colorless spores are larger that the mature dark colored 



ones. The cause of this secondary reduction in size is not ex- 



. plained; it may be a degenerative process, since the oldest and 



darkest spores are more or less structureless. 



Most of the representatives of the genus are northern in their dis- 

 tribution. The majority occur upon rocks ; a few upon the soil. 



PLATE 39. 



Urceolaria scruposa (L.) Nyl. 



1. Natural size. 



2. Apothecium and portion of thallus magnified. 



3. Section of apothecium. 



4. Section of thallus. 



5. Paraphyses and spore-sac. 



6. Spores, a, colorless immature spore ; b, mature spore. 



7. Algae. 



2. Haematomma Mass. Mem. Lich. 32. 1853. 



This group is usually combined with Lecanora ; but it has, however, 



strongly marked spore-characters, which have led me to maintain the 



genus. There is no doubt that it is closely related to Lecanora, 



but it is rather difficult to decide whether it is phylogenetic- 



