SCYTONEMEJE;. 265 



Scytonema myochrous. Ag. Syst. p. 40, No. 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. Harr. 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. ; b, portion of 

 same X 400 ; c, hormogones X 400. 



Scytonema natans. Breb. in Kutz. Tab. Phyc. II., t. 22, /. 1. 



Floccose tomentose, green then brown or olive, trichomes 

 slender, elongated, becoming brownish, internally seruginous 

 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, 



2 P 



