•204 L1CHENES. [Sticia. 



Stones and walls, rarely on trees in Scotland, but not general : and 

 always barren. 



29. P. parietina, Ach. {yellow wall Parmelia); thallus orbi- 

 cular brigbt-yellow the lobes marginal radiating appressed 

 rounded crenate and crisped granulated in the centre, beneath 

 paler and fibrillose, apothecia deep-orange concave with an en- 

 tire border.— Ach. Syn. p. 200. — Lichen parwtifms, Linn. — E. 

 Bot. t. 194.— Dill. Muse. t. 24. f. 76. 



On trees and walls, abundant. 



** Thallus with its segments inflated at the extremity. 



30. P. physodes, Ach. {inflated Parmelia); thallus orbicular 

 stellated glaucous-white the segments sinuato-multifid convex 

 glabrous inflated often bearing elevated powdery warts, beneath 

 brownish-black, apothecia red-brown with a thin elevated bor- 

 der. — Ach. Syn. p. 218. — Lichen physodes, Linn — E. Bot. 

 t. 126.— Dill. Muse. t. 20. /. 49. 



Trunks of trees, stones, and low bushes, not unfrequent. Apothecia 

 very rare : on an ash-tree, near Dumfries, Dr. Richardson. 



31. P. diatrypa, Ach. {double-coated Parmelia) ; thallus substel- 

 late greenish-grey, the segments sinuato-multifid nearly plane 

 smooth bearing powdery warts and perforated the extremities 

 inflated, apothecia reddish-brown the border inflexed entire — 

 Ach. Syn. p. 219. — Lichen diatrypus, Ach. Prodr. — E. Bot. 

 t. 1248. 



Wet rocks, among moss, rare. Foot of Snowdon, Mr. D. Turner. 

 At Ballacheulish, bearing apothecia, Turner and Hook.— Smaller than 

 the last, with narrower segments ; forming, however, with it, a small but 

 natural groupe of the Genus, distinguished by the thallus, especially at 

 the extremity, being hollow and having a distinct upper and lower mem- 

 brane. The P. enteromorpha, from the N. W. Coast of America, is a 

 still more remarkable example of this tribe. 



19. Sticta. Ach. Sticta. 



Thallus foliaceous, coriaceo-cartilaginous, spreading, lobed, 

 free and downy beneath, with little cavities or Iwllow spots 

 {cyphellai) often containing a pow r dery substance. Apothecia 

 {scutellce) beneath formed of the thcdliis, to Avhich they are ap- 

 pressed and fixed by a central point, the disk coloured, plane, 

 surrounded by an elevated border formed of the thallus. — Name; 

 (jtizto;, dotted, from the depressed spots, or cyphellce, with which 

 the under-side of the thallus is dotted ; and which is indeed the 

 only technical character by which the Genus is distinguished 

 from Parmelia. " These," Mr. Borrer observes, " vary much 

 in their nature : in a few species they are merely irregular bald 

 spots, apparently proceeding from abrasion of the surface ; in 

 others, they are powdery warts, soredia, without a margin ; and 

 again, in others, as in S. macrophylla, little pits {cyphellcE,) fur- 

 nished with a margin from the superficial membrane of the thallus 

 within which they are originally formed : these cyphellce also 



