SCYTONEMER. 267 
Genus 108. PETALONEMA, Berk, (1832.) 
~ 
Trichomes enclosed in a very broad striate membranous 
sheath, which forms a transparent layer, resembling « hyaline 
wing. 
Threads as in Scytonema, with the sheath very broad, forming a 
transparent layer around the trichome, 
Petalonema alatum. Berk. Glean. t. 7, f. 2. 
Forming a thin brown stratum. Trichomes small, 4 few 
lines only in length, winged, obtuse, with numerous strie, 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. 
Sizz. Trichomes ‘01 mm., with sheath from :05 to ‘12 mm. 
Hass. Alg. 238, t. 68, f. 6. Harv. Man. 168. 
Arthrosiphon alatus, Rabh, Alg. Eur. ii., 265. 
Arthrosiphon Grevillei, Kutz. Sp. Alg. 311. Fischer Nost, 
f. 10. 
Oscillatoria alata, Grev. Sc. Crypt. Flora, t. 222. 
On rocks exposed to the trickling of water. 
Plate CVII, fig. 1, Upper portion of trichome with sheath X 400 
diam. 
Genus 109. SYMPHYOSIPHON. Kutz. (1843.) 
Trichomes as in Scytonema. Filaments agglutinated in erect 
wick-like bundles. 
Symphyosiphon Hoffmanni. Kutz. Tab. Phyc. 11., t.48, f. 3. 
Terrestrial, resembling a Symploca in habit. Tufts small, 
ascending, dark brown; trichomes simple, erect, loosely col- 
lected in pointed fascicles, internally pale eruginous 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 Hoffmanni, Agardh Syst. p. 40. Rabh. Alg. 
Eur. ii., 259. 
