SCYTONEMEJE. 267 



GENUS 108. PETALONEMA. Berk. (1832.) 



Trichomes enclosed in a very broad striate membranous 

 sheath, which forms a transparent layer, resembling a hyaline 

 wing. 



Threads as in Scytonema, with the sheath very broad, forming a 

 transparent layer around the trichome. 



Fetalonema alatum. Berk. Glean, t. 7, f. 2. 



Forming a thin brown stratum. Trichomes small, a few 

 lines only in length, winged, obtuse, with numerous stride, when 

 taken in conjunction with the wings or membranous expansions, 

 they are linear and plane. Each wing is about thrice the 

 breadth of the proper filament, of a white colour, somewhat 

 transparent, of a bright yellow next the filament, and exhibiting 

 under a favourable light a numerous series of transverse lines 

 or folds. Endochrome of the central thread greenish and 

 septate. 



SIZE. Trichomes -01 mm., with sheath from -05 to -12 mm. 



Hass. Alg. 238, t. 68, f. 6. Harv. Man. 168. 



Arthrosiphon alattis, Rabh. Alg. Eur. ii., 265. 



Arthrosiphon Grevillei, Kutz. JSp. Alg. 311. Fischer Nost. 

 f. 10. 



Oscillatoria alata, Grev. Sc. Crypt, Flora, t. 222. 



On rocks exposed to the trickling of water. 



Plate CVII, f,f/. 1, Upper ' portion of trichome with sheath X 400 

 diam. 



GENUS 109. SYMPHYOS1PKON. Kutz. (1843.) 



Trichomes as in Scytonema. Filaments agglutinated in erect 

 wick-like bundles. 



Symphyosiphon Hoffmann!. Kutz. Tab. Pliyc. u., .43, /. 3. 



Terrestrial, resembling a Symploca in habit. Tufts small, 

 ascending, dark brown ; trichomes simple, erect, loosely col- 

 lected in pointed fascicles, internally palo geruginous green, 

 sometimes interrupted, joints delicately granulose, inferior 

 cylindrical, thin, superior thicker and more or less swollen. 

 Sheath firm, broad, attenuated upwards, rarely acute, colourless, 

 or yellowish towards the base. Heterocysts intercalated, 

 globose, hyaline. 



SIZE. Trichomes -01 mm. diam., with sheath -012--014 mm. 



Scytonema Hoffmcnnri, Agardh Syst. p. 40. Rabh. Alg. 

 Eur. ii., 259. 



