GENERA AND SPECIES. 167 



since the thallus is less rigid than the hair of the 

 horse's tail. 



B.jubata, and perhaps also other species, yields a 

 red dye. Reindeers feed upon it when Cladonia ran- 

 giferina is not obtainable. Laplanders are said to 

 cut down the trees upon which it grows so that the 

 reiudeer may have more ready access to the lichen. 



13. Usnea. 



Thallus fruticose, pendulous, large, much branched ; 

 lobes cylindrical, or rarely flattened, decreasing in 

 size in an acropetal (toward apex) direction. Main 

 branch quite thick and rigid. The surface is less 

 smooth than in the thalli of Alectoria and Bryopogon ; 

 often it is circularly fissured. Soralia are quite rare. 

 Upon making a transverse section of the thallus it is 

 found to contain a rather firm central core of longi- 

 tudinal hyphae. The prevailing colors of the thallus 

 are grayish-green, pale brownish-green or straw color. 

 The apothecia are very variable in size, lateral to 

 terminal. Spores small, simple, elliptical, colorless. 



The Usneas are somewhat northern in their range. 

 They occur upon trees in the higher altitudes. Con- 

 siderable confusion exists as to the limitations of some 

 species and varieties, as, for example, Usnea harhata 

 and its real or imaginary varieties. The following 

 are the more common species irrespective of varieties. 



1. Usnea linearis. Thallus medium, of several 

 main branches, bearing numerous long, slender, cylin- 

 drical branches ; greenish-gray. No fertile specimens 

 have come to notice. 



