Notes on the Blue-green Alge, ete. 403 
53. Stratum thin, membranaceous, pale blue-green .. P. tenue 
Filaments straight, entangled ; sheaths 
thin, becoming diffluent into a mucus; 
trichomes I-2 mic. in diameter, slightly 
constricted at joints; cells 2-5-5 mic. 
long; apex straight, or may become 
curved; apical cell acute conical, not 
capitate, no calyptra; transverse walls 
usually indistinct. In fresh water; on 
pots in a greenhouse, etc. (G., 189, 4, 
23-25; ie 98, 4, 63-65.) 
53. Stratum thick, impregnated with lime, firm, bluish 
green to brownish-red a P. crosbyanum 
Filaments curved, sheaths thin;  tri- 
chomes 1I-2mic. in diameter, not con- 
stricted at joints; cells 1-5-5 mic. long; 
apex straight, not tapering, not capitate ; 
apical cell conical, no calyptra. Empty 
sheaths numerous. In salt water. (T., 
96, 4, 60-61.) 
54. Irichomes more than 3 mic. in diameter... rs Se 7 
54. Filaments less than 3 mic. in diameter Be ad HO TES 
55. Irichome not capitate; apical cell rounded with 
slightly thickened membrane .. P. ambiguum 
Stratum black, yellow-green or blue- 
green; sheaths firm or diffluent, some- 
times thick and lamellose; trichomes 
slightly constricted at joints; transverse 
walls rarely granulated; cells 4-6 mic. 
in diameter, 1-5-2-7 mic. long. In fresh, 
brackish, or warm water. (G., 189, 5, 
EQ; DEO 3 a 5} 
55. Irichome not capitate, apical cell conical, obtuse, P. interruptum 
Stratum membranaceous, mucous, blue- 
green; trichomes 5-6:5 mic. in diameter, 
flexuous; cells 2:5-3:2 mic.” long, trans- 
verse walls finely granulated. (T., 102, 
4, 75:) 
56. Stratum thin, membranaceous, pale blue-green 
or yellow .. Si: a Be P. laminosum 
Filaments flexuous, not constricted at 
joints, entangled ; sheaths narrow papery 
or amorphous; cells 1-1-5 mic. in dia- 
meter, 2-4mic. long; four refringent 
granules on transverse walls; apical cell 
acute conical, not capitate, no calyptra. 
In hot springs and sulphur waters; in a 
greenhouse, on rocks moistened by water, 
ete. (Gil i876 ae) “L.? O6;) 45.623) 
Var. weedii, see Tilden, page 97. 
56. Stratum thin, scarlet .. 2a zs ee cpr 
Filaments straight; trichomes I mic. 
in diameter, fragile, not constricted at 
joints; cells 1-1-2 mic. long, transverse 
walls rarely visible. Thermal. (T., 95, 
4, 58.) 
57° Trichomes 6-8 mic, in diameter... a 2 
Stratum dark, velvety, lead-coloured ; 
trichomes spiral or straight and uncinate 
at apex, constricted at joints; apical 
O. boryana 
1913 Nov. 1. 
