158 GUIDE TO THE STUDY OF LICHENS. 



species there is a yellow coloration. Cilia are fre- 

 quently present; soralia are comparatively rare. 



The apothecia are of medium size, discoid, usually 

 less markedly cup-shaped than in Parmelia. Disk 

 chestnut-brown, shining, margin somewhat crenate 

 or torn. The spores are simple, elliptical and color- 

 less, somewhat smaller than in Parmelia, 



Most of the Cetrarias are northern, occurring upon 

 trees and rocks. 



1. Cetraria Fahlunensis. Thallus foliose, much 

 branched, smooth, somewhat ascending, marginal lobes 

 olive-brown to nearly black above ; dark beneath 

 with numerous rhizoids. Apothecia few, medium to 

 large, thin. Disk chestnut-brown, smooth. Spores 

 typical, 8/x X 6.5/x. 



This lichen furnishes a red (vermilion) dye. 



2. Cetraria ciliaris. Thallus foliose and much 

 branched, lobes somewhat ascending and cilia te, 

 smooth ; ash-gray tinged with bluish-green above, 

 light-brown beneath, rhizoids few. Apothecia medium 

 to large, margin crenulate or torn. Disk chestnut- 

 brown, smooth. Spores typical, spherical, 6/x. 



3. Cetraria juniperina. Thallus foliose, medium 

 size, branched, terminal lobes ascending, lacerate ; 

 straw color on both surfaces. Apothecia of medium 

 size, margin crenate. Disk chestnut-brown. Spores 

 typical, S/x X 6.5/x. 



Upon boiling in water this lichen yields a yellow 

 coloring-matter which was much used in Sweden for 

 dyeing home-made cloth fabrics and Easter eggs. With 

 Placodium murorum it was at one time highly rec- 



