133 



that the thallus-characters of Biatora resemble Parmelia more nearly 

 than those of Psora. 



The representatives of this genus are widely distributed in the 

 territory ; they are most common upon the bark of trees ; less com- 

 mon upon rocks and upon mosses. The limitations of the species 

 are rather uncertain and there is considerable confusion in their sys- 

 tematic arrangement. 



PLATE 17. 

 Biatora varians (Ach.) Tuck. 



1. Plants natural size; a, clusters of apothecia. 



2. A cluster of apothecia magnified. 



3. Section of apothecium. 



a, thecium ; b and c, hypothecium. 

 d, algal layer. 



4. Section of thallus. 



5. Spore-sacs with spores and paraphyses. 



6. Spores. 



4. Bilimbia De Not. Giorn. Bot. It. 2: 190. 185 1. 



The characters of this genus gradually merge into those of 

 Lecidioj>sis, the only essential difference being in the color, which 

 is, however, not more marked than in Biatora and Lecidea. It is 

 sincerely to be hoped that some investigator will take into considera- 

 tion the significance of color-differences in lichens, especially in the 

 lower forms ; this would aid very materially in giving more definite 

 limitations to the genera. 



Only a few representatives of this genus have been observed 

 within the territory. The thecium and hypothecium are colorless ; 

 the spores are spindle-shaped, colorless, usually four-celled, and the 

 thallus is crustaceous, and to my knowledge never becomes foliose 

 in character, which would place the genus below Biatora. I have, 

 however, not attempted to follow out a strict phylogenetic relation- 

 ship of the lower genera, since they are not sufficiently known. 



The apothecia are of medium size, the disk is flattened or con- 

 vex, and varies in color from yellowish brown to dark brown. 



The algae are Cystococcus humicola and differ somewhat from the 

 ordinary forms in being smaller and more united in colonies. They 

 are intimately enclosed by haustorial branches, very frequently form- 

 ing soredia, especially in B. s-phaeroides. There is evidently an in- 



