—23— 



Fig. 3. 



Physcia aquila var. 

 detonsa X 2. 



Physcia aquila (Ach.) Nyl., var. 

 DETONSA TucKM. (Fig. 3.) This in- 

 teresting lichen is found on rocks, occa- 

 sionally on trees. In favorable locali- 

 ties it grows in round patches, the outer 

 ring lighter and smoother than the inner 

 part, which gives it the specific name, 

 '* detonsa," meaning shaved. The thal- 

 lus at the margin is olive in color, but 

 soon grows brown. The lobes are linear, 

 fringed on the margins with cilia, to- 

 ward the centre are thickly covered with 

 isidioid lobules. Beneath, the thallus is 

 white with black fibrils, which form a thick black mat. The apothecia are 

 rather small and are sessile, the disk is flat, dark brown, with a toothed, 

 rough looking margin. The apothecia are numerous and are crowded in 

 between the isidioid lobules, giving the surface a very rough appearance. 



Physcia OBscuRA (Ehrh.) Nyl. (Fig. 

 4). The thallus of this interesting and 

 variable lichen is brownish, the lobes are 

 linear, many-cleft, and flat, fringed with 

 short dense black bristle-like fibrils. The 

 under side is so thickly covered with short 

 black bristles that it looks black, and in 

 Fig. 4. Physcia obscitra. some specimens it really is, in others it is 

 light at the margin. The apothecia are a very dark brown, the disk flat, the 

 margin thickly beset with spine-like fibrils. It is found on mossy rocks and 

 on trees. 



Physcia setosa (Ach.) Nyl. This lichen belongs to the obscura 

 group, and resembles it very closely. The thallus is larger, the lobes are 

 not so finely cut, and the color is not so dark. The lobes are fringed with 

 black fibrils as are those of P. obscura, but not so densely. The apothecia 

 are larger and are not surrounded by the stiff black fibrils but have a crenu- 

 late margin. With some lichenists this is not made a distinct species, but a 

 variety of P. obscura. 



Physcia pulverulenta (Schreb.) Nyl. 

 (Fig. 5). Thallus covered with a fine white 

 powder or dust which gives it a roughened, 

 silvery appearance. The lobes are crenate 

 with rounded tips. P. pulverulenta resembles 

 P. speciosa but can be distinguished from it 

 by the pruinose surface. Beneath the thallus 

 is covered with black fibrils which form a close 

 I pulverulenta. nap. The apothecia are of medium size, ses- 

 sile, the disk flat, darker than the thallus, with the same silvery bloom; it is 

 bordered with a thick lobulate or leaf -like margin. 



