SCYTONEME. 265 
Scytonema myochrous. 4g. Syst. p. 40, Wo. 13. 
Stratum thin, woolly, dark brown (now and then rather 
silky); trichomes very thick, brown, lucid, slightly curved, 
ascending, blue-green within, reddish at the apex (5-6 terminal 
joints), distinctly articulate, pseudo-branches for the most part 
in pairs, sometimes very long, flaccidly erect, about half the 
thickness of the trichomes ; sheath of the trichomes thick, dis- 
tinctly lamellose, firm, beautiful yellow-brown, surface quite 
smooth, that of the branches paler, often colourless at the tips, 
closed and obtusely rounded, heterocysts oblong or sub-cylindri- 
cal, colourless, about equal to the inner diameter of the 
trichomes, 
Size. Cells 01 mm. diam., with sheath ‘03 mm. diam. 
Rabh. Alg. Eur. ii., 254. Hass. Alg. 237, t. 68, f. 2. 
Jenn, Tunb. Wells, 188. Gray. Arr.i., 285. Eng. Bot. ii, t. 
2515, t. 2516. Kirch. Alg. Schl. 225. Harv. Eng. Fl. v., 
365. Harv. Man. 155. Mack. Hib. 236. 
Conferva myochrous, Dillw. Conf. t. 19. Eng. Bot. i, t. 
1555. 
On moist rocks. 
Plate CV. fig. 1. a, threads magnified about 60 diam.; 8, portion of 
same X 400; c, hormogones Xx 400. 
Scytonema natans. Breb. in Kutz. Tab. Phyc. 11., t. 22, f. 1. 
Floccose tomentose, green then brown or olive, trichomes 
slender, elongated, becoming brownish, internally sruginous 
green, distinctly articulate, joints nearly equal, granular, pseudo- 
ramuli often in pairs, very slender, more or less distant, very 
shortly articulated, sheaths firm, lamellose, yellow or brownish, 
rarely uncoloured, branches paler, or colourless, indistinctly 
lamellose, heterocysts interspersed, oblong, or ovoid, pellucid. 
Size. Threads with sheath ‘025 mm., without sheath :007 
mm. 
Rabh. Alg. Eur, ii., 253. Kirch. Alg. Schl. 224. 
In stagnant water. 
Plate CV. fig.2. Portion of trichome with sheath X 400 diam. 
Scytonema cinereum. Meneg. in Kutz. Spec. 303. 
At first pulvinate, cinereous green, then confluent, forming a 
more or less tomentose pulverulent stratum (becoming pale blue 
when dry), now and then violet or purplish; trichomes very 
fragile, elongated, flexuose and curved, loosely interwoven, 
sparingly branching, indistinctly articulate, internally dingy, 
2P 
