NORTH AMERICAN USNEACEAE. 145 
Famity: Usneacee Eschw. System. Lich. 23. 1824. 
Diagnosis: Thalline cortex contiguous: cylindrical or 
angular, bifacial or deformed. 
Apothecia lecanorine. Gonidia Protococcoid. 
Description: Thallus fruticose or filamentous, radial or 
bifacial; gray, yellow, green, brown or black. Gonidia 
Protococcoid. Apothecia lecanorine (having a thalloid 
exciple), marginate or emarginate, entire, crenulate or 
ciliate, disk concolorous, yellow, brown, or black. 
Spores monoblast, bilocular to muriform—hyaline or 
colorate. 
The Usneacex, from their size and conspicuous character, 
are commonly recognized, though often by the laity as 
mosses. They are represented in all the zones of our area, 
and are found growing on earth, rocks and trees. Like most 
lichens, for their highest development they need not only 
moisture, but abundant light. Economically they possess 
little practical value, though certain species have been used 
for food (Cetraria islandica), for medicine (Usnea florida) 
and for dyes (Letharia vulpina). It is doubtful if they are 
appreciably injurious to trees. They are evidently very 
sensitive to atmospheric conditions, and their presence is in- 
dicative of pure air, for the partial cleansing of which they 
are no doubt responsible. As only a few species (Ramalina, 
Usnea) of this family are rock forms, they play little part 
in the disintegrations which produce soil.® 
TriBE: Usneee Hue Lich. extra Europ. 31. 1899. 
Cortical structure complex (decomposed). 1. ¢. 11.28. 
Medulla arachnoid. 
(To be continued.) 
9 See Herre, Proc. Wash. Acad. 12 :218. 1910—Ramalina homalea. 
