256 HERRE 



Thallus orbicular or stellate, appressed; lobes discrete, narrow, 

 elongate, many-cleft; their margins crenate or entire; usually up- 

 turned and confluently sorediate; thallus often becoming powdery 

 sorediate or crustose at the centre, and now disappearing, leaving 

 only the marginal lobes. 



Varies from the type in having the thallus of a silvery white color; 

 rarely darker or dingy. Medullary layer white or greenish white. 



Apothecia rare, the disk pruinose; margin thick, sorediate, entire, 



or sometimes slightly dentate; spores — ^ — n. 



25 - 32.5 



Common on trees in the foothills and mountains. 



3. PHYSCIA PULVERULENTA ISIDIIGERA A. Zahlbr. 



Physcia pulverulenta isidiigera A. Zahlbruckner, in litt. 



Physcia pulverulenta isidiigera Herre, Proc. Wash. Acad.Sci. 7: 362. 



1906. 

 Physcia pulverulenta isidiigera Hasse, Bull. So. CaHf. Acad. Sd. 5 : 



39. 1906; Ventura County and Mt. San Jacinto. 



Thallus orbicular, marginally closely appressed and thin; becom- 

 ing thick, heaped, and isidiose powdery or granular in the central 

 portion, all trace of lobes being lost; marginal lobes short, crenate, 

 imbricate; color brownish or dingy black; often bluish pruinose, the 

 plant then of a pale, bluish-slate color; beneath black, the margin 

 pale; covered with short black fibrils; medulla greenish white. 



Apothecia small, the disk black, occasionally pruinose; margin 



thick, tumid, elevated, sorediate; spores — ^ n. 



Z^ - 37-5 

 On trees, roofs, and fences. Very common in the lowlands about 



San Francisco Bay and back to the foothills, growing in great abim- 



dance in the shade or where exposed to the moist bay winds. 



4. PHYSCIA VENUSTA (Ach.) Nyl. 



Parmelia venusta Ach. Meth. Lich. 211. 1803. 



Physcia venusta Nyl. Bull. Soc. Bot. Fr. 25: 383, pi. 25. 1878. 



Physcia venusta Herre, Proc. Wash. Acad. Sci. 7: 363. 1906. 



Thallus expanded, orbicular, appressed; lobes many-cleft, narrow, 

 laciniate or crenate, the tips usually rounded; inner lobes often 



