232 



MCHEXACEI. 



[EVERXTA. 



Form 3. ceratea Nyl. Lich. Scand. (1801) p. 73. Thallus de- 

 cumbent ; laciniae narrow, convex and subcylindrical, acuminate, 

 subglabrous. Cromb. Grevillea, vi. p. 21. Parmelia furfuracea 

 /3. ceratea, Ach. Meth. (1803) p. 255. Brit. EO.-S. : Cromb. n. 139. 



Distinguished by the form of the more naked laciniae ; but intermediate 

 states occur, in which these characters are less marked. With us it is 

 always barren, though Ac-harms (Lich. Univ. p. 501) says the apothecia 

 chiefly occur in this form. 



Hal. On rocks and old walls in upland districts. Dlstr. Seen only 

 from a few localities in S.W., Central, and N. 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. Per.tland Hills, near Edin- 

 burgh; Glen Falloch, Perthshire; Deerhill Wood, Forfarshire ; near 

 Countesswells, Aberdeen. 



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

 i. (1860) p. 375. Thallus foliaceous, horizontally expanded or 

 rarely ascending, variously 

 lobed and laciniate ; epi- 

 thallus somewhat shining, 

 beneath usually fibrilloso- 

 rhi/.inose ; medullary layer 

 woolly, composed of fila- 

 ments loosely interwoven ; 

 cortical layer thin, formed 

 of minute cells with thick- 

 ened walls. Apothecia scat- 

 tered, scutelliform, with thai- 

 line margin ; hypothecium 

 colourless, thccae short, the 

 wall thickened above ; spores 

 usually 8na\ ellipsoid, simple, 

 colourless ; h} menial gelatine 

 bluish with iodine. Spermo- 

 gones generally scattered, 

 at length slightly prominent, 

 blackish ; sterigmata 2-5- 

 articulate; spermatia acicular, 



fusiformi-incrassate at either 

 apex. 



Fig. 44. 



Parmelia perlata Ach. a. Fragment of the 

 thalamium and a theca, X350. b. Three 

 spores, x 500. c. Vertical section of the 

 thallus, with two spennogones, X 30. 

 d. Sterigiuala and spermatia, X&00. 

 c. Three gonidia, x 350. 



The species vary in habit, 

 but are for the most part hori- 

 zontally expanded, and rarely 

 fruticulose. In no other genus 

 are the reactions of more value 

 in discriminating species, which were often not distinguished from 

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



