CE IRAKI A.] 



CETRARIEI. 



215 



y 



Fig. 42. 



Cetraria Islandica Ach. — a. A theca, 

 xSoO. b. Spiires, x500. c. Ver- 

 tical spction of a spermogone. x3(). 

 d. Steriginata and spenuatia, X 5W. 



;Mt. CETRARIA Ach. Mcth. (1803) p. 292 pro parte; Nyl. Syn. 

 i. p. 298. — ThiiUus fruticulose, erector ascending, more or less rigid, 

 laciiiiose, rarely tistulose, coiicolo- 

 rous on both sides ; epithallus 

 somewhat shining; medullary 

 layer with the filaments loosely 

 interwoven, or in the fistulose 

 species arachnoid, scanty, intri- 

 cate within ; cortical layer inter- 

 nally formed of longitudinal tubes, 

 externally cellular. Apothecia 

 subconcolorous with the thallus, 

 marginal, adnate on the front of 

 the apices of the lacinia^ usually 

 with entire, sometimes with cre- 

 nulate margin ; hypothecium 

 colourless; spores subellijisoid ; 

 hyiuenial 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-alpiue 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 whicli they are enclosed being 

 abraded. 



1. C. Islandica Ach. Meth. (1803) p. 293.— Thallus subfoliaceous, 

 caespitose, variously laciniate, subcanaliculate, more or less ciliato- 

 spinulose at the margins, shining, pale-chestnut-coloured or dark- 

 chestuufc-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 laciniae, 

 large or moderate ; the margin thin, entire or crenulate, at length 

 excluded: spores 0,007-11 mm. long, 0,004-6 mm. thick. — Gray, 

 Kat. Arr. i. p. 433 ; 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 Islandica, Mudd, 

 Man. p. 77, t. 1. f. 19. Lichen Islandiciis Linn. Sp. PL (1753) 

 p. 1145 a : Huds. Fl. Angl. p. 448 ; Lightf. Fl. Scot. ii. p. 829 ; Eng. 

 Bot. t. 1330 ; With. Arr. ed. 3, iv. p. 54. Lichenoides riijidum 

 en/ngii foliis refer ens Dill. Muse. 209, t. 28. f. 111a, in Ray, Syn. 

 ed. 3, p. 77, n. 90. — Brit. Exs. : Mudd, n. 51 ; Leight. n. 42 pro 

 parte. 



The thallus of the '' Iceland Moss " varies considerably in colour, being 

 sometimes almost entirely grevish-white, and in the character of the 

 laciniae. The fertile laciniie are broader at the apices than the barren. 

 The apothecia, which are seldom met with in this country, are usually of 

 moderate size, and become at length somewhat deformed. The spermo- 



