CEIRARTA. ] CETRARIET. 215 
_ 39. CETRARIA Ach. Meth. (1803) p. 292 pro parte; Nyl. Syn. 
1. p. 298.—Thallus fruticulose, erect or ascending, more or less rigid, 
laciniose, rarely fistulose, concolo- 
rous on both sides; epithallus ae 
somewhat shining; medullary () 3 ‘Uy 
layer with the filaments loosely Za-\\ 
interwoven, or in the fistulose , 
species arachnoid, scanty, intri- S M 
a 
cate within; cortical layer inter- 
nally formed of longitudinal tubes, a 
externally cellular. Apothecia oe 
subconcolorous with the thallus, Fie. 42 
marginal, adnate on the front of sai 
the apices of the lacinia, usually Cetraria Islandica Ach.—a. A theca, 
with entire, sometimes with cre- 800. 2. Spores, x500. ¢. Ver- 
. : tical section of a spermogone, x30. 
nulate margin; hypothecium sg, Sterigmata and spermatia, x 50. 
colourless; — spores subellipsoid ; i 
hymenial gelatine bluish with iodine. Spermogones marginal, 
spinuliform ; sterigmata simple ; spermatia cylindrical, moderate or 
somewhat short. : 
This genus is especially characteristic of sub-arctic or alt-alpine regions. 
The thallus, which is of a lighter or darker spadiceous colour, becomes at 
length free from the substratum. In most species the apothecia are very 
rare or unknown in this country, and even the spermogones, which are 
more frequent than the apothecia, are seldom seen in herbaria specimens, 
in consequence of the spinules in which they are enclosed being 
abraded. 
1. C. Islandica Ach. Meth. (1803) p. 293.—Thallus subfoliaceous, 
cxspitose, variously laciniate, subcanaliculate, more or less ciliato- 
spinulose at the margins, shining, pale-chestuut-coloured or dark- 
chestnut-brown, usually with impressed white soredia at the back, 
often stained of a blood-red colour at the base (K—, CaCl—). 
Apothecia adnate on the upper surface of the apices of the lacinie, 
large or moderate; the margin thin, entire or crenulate, at length 
excluded; spores 0,007-11 mm. long, 0,004-6 mm. thick.—Gray, 
Nat. Arr. i. p. 483; Hook. Fl. Scot. ii. p.51; Sm. Eng. Fl. v. 
p. 221; Tayl. in Mack. Fl. Hib. ii. p. 155; Cromb. Lich. Brit. p. 25; 
Leight. Lich. Fl. p. 96, ed. 3, p. 91.—Cornicularia Islandia, Mudd, 
Man. p. 77, t.1.f. 19. Lichen Islandicus Linn. Sp. Pl. (1753) 
p.1145 a; Huds. Fl. Angl. p. 448; Lightf. Fl. Scot. ii. p.829; Eng. 
Bot. t. 1830; With. Arr. ed. 3, iv. p. 54. Lichenoides rigidum 
eryngii folis referens Dill. Muse. 209, t. 28. f. 1114, in Ray, Syn. 
ed. 3, p. 77, n. 90.— Brit. Evs.: Mudd, n. 51; Leight. n. 42 pro 
parte. 
The thallus of the “Iceland Moss” varies considerably in colour, being 
sometimes almost entirely greyish-white, and in the character of the 
lacinize. The fertile laciniz are broader at the apices than the barren. 
The apothecia, which are seldom met with in this bret are usually of 
moderate size, and become at length somewhat deformed. The spermo- 
