140 GUIDE TO THE STUDY OF LICHENS. 



medium, branching; lobes linear, slender, pale-gray 

 above, with darker soralia, slightly darker beneath, 

 with rigid rhizoids. Apothecia not seen. 



5. Physcia tribacea. Thallus rather small, minutely 

 branched, lobes not uniform in size, crenulate, greenish- 

 gray above, light color beneath, rhizoids few. Apothe- 

 cia small to medium, margin entire. Disk dark-brown 

 to black. Spores brown, oblong, ovoid, 17/x X 8/x. 



6. Physcia stellaris. Thallus rather small, branched, 

 lobes of uniform width, lying flat upon the substratum, 

 ash-gray to brown above, light-brown beneath, rhizoids 

 comparatively few. Apothecia as in P. tribacea. 

 Spores brown, typical, 19/x X 10.0/>t. 



7. Physcia pulverulenta. Thallus large, branched, 

 lobes variable from linear to broad, brittle, sometimes 

 bearing minute conical or strap-shaped outgrowths ; 

 light-gray to brown, overspread by a translucent white 

 coloration. Apothecia medium to large, margin slightly 

 elevated and bearing conical or warty outgrowths. Disk 

 dark-brown, with a translucent white coloration. Spores 

 dark-brown, constricted in the middle, connecting thread 

 not distinct, 32.5/x X 17/x. 



8. Physcia aquila. Thallus large, much branched, 

 lobes linear, gray to brown above, nearly the same 

 color below with large dark rhizoids, older parts of 

 thallus and apothecia bearing numerous conical out- 

 growths or small thalloid lobules. Apothecia medium, 

 margin often isidioid. Disk dark-brown. Spores 

 large, brown, 29.0/x X 18.0/x. 



9. Physcia hyjjoleuca. Thallus large, branched, ad- 

 herent to the substratum, ash-gray above, pale beneath, 



