232 



LILHKXACEI. 



[dterxta. 



Form 3. ceratea Nyl. Lich. Scand. (Ib61) p. 73. — Thallus de- 

 cumbent ; lacinia^ Barrow, convex and suVjcyliudrical, acuminaie, 

 sub£;labrous. — Cromb. Grevillea, vi. p. 21. — Parmelia farjuracea 

 fy. ceratea, Ach. Meth. (1803) p. 2oo,—Brit. E.vs. : Crom'b. n. 139. 



Distinguished bv the form of the more naked lacinise : but intermediate 

 states OCCIU-, iu which these characters are less marked. With us it is 

 always barren, though Aeharius (Lich. Univ. p. 501) says the apothecia 

 chiefly occur in this form. 



Hfib. On rocks and old walls in upland districts. — Distr. Seen only 

 from a few localities in S.W., Central, and X. England, S. and N.E. 

 Scotland, and the S.W. Highlands. — B. M. : Hunter Tor, Dartmoor, 

 Devonshire; Helminton, Cornwall ; near Buxton. Derbyshire; Winder- 

 mere, Westmoreland ; Alston, Cumberland. Pentland Hills, near Edin- 

 burgh ; Glen Falloch, Perth.shire ; Deerhill Wood, Forfarshire ; near 

 Countesswells, Aberdeen. 



■i'' '1 v/ (1 I' \\ 



42. PARMELIA Ach. Meth. (1803) p. 153 pro parte ; Xyl. Syn. 

 i. (1860) p. 375. — Thallus foUaceous, borizoutally expanded or 

 rarely ascending, variously 

 lobed and laciniate ; epi- 

 thaUus somewhat shining, 

 beneath usually fibrilloso- 

 rhizinose ; medullary layer 

 woolly, composed of fila- 

 ments loosely interwoven : 

 cortical layer thin, formed 

 of minute cells with thick- 

 ened walls. Apothecia scat- 

 tered, scutelliform, A\ith thai- 

 line margin ; hypothecium 

 colourless, thecte shoil;, the 

 wall thickened above ; spores 

 usually Sntc. ellipsoid, simple, 

 colourless ; hymenial gelatine 

 bluish Avith iodine. Spermo- 

 gones generally scattered, 

 at length slightly prominent, 

 blackish ; sterigmata 2-5- 

 articulate; spermatia acicular, 

 fusiformi-incrassate at either 

 apex. 



m 

 m 



Fig. 44. 



Parmelia pirlata Ach. — a. Fragment of the 

 thalaiuiui'.i and a theca, x3.'.0. b. Three 

 spores, x500. c. Vertical section of the 

 thallus, with two sperniogones, X 30. 

 cl. Sterigiuala and speriuatia, xoUO. 

 c. Three gouidia. x 35U. 



The species vary in habit, 

 but are for the most part hori- 

 zontally expanded, and rarely 

 fruticuiose. In no other geiuis 

 are the reactions of more value 

 in discriminating .-pecies, which were often not distinguished from 

 each other, or were regarded merely as varieties, forms, and stales. 



