100 
PACIFIC SCIENCE, Vol. XI, January, 1957 
91. Medullary cells all similar and more or 
less isodiametrical in cross section. .92 
91. Thallus in cross section showing min- 
ute rhizoidal filaments between the 
medullary cells. . .Gelidium (crinale) 
92. Growing points consisting of an apical 
cell, either emergent or in an apical pit 
95 
92. Apices without a single apical cell. . . 93 
93. Branching irregular, but not markedly 
divaricate; thalli very slender and wiry 
94 
93. Branching markedly divaricate; thalli 
moderately coarse and succulent 
Chnoospora 
94. Tetrasporangia and antheridia borne in 
swollen, terminal stichidia; thalli form- 
ing small tufts and clumps ; main branches 
mostly 175-250 /jl in diameter 
Gelidiopsis 
94. Reproduction not to be expected; thalli 
forming wiry mats ; main branches (100) 
140-230 /jl in diameter. . Wurdemannia 
95. Apical cell in a terminal pit 96 
95. Apical cell emergent 97 
96. Thalli erect or with creeping and erect 
branches, with many very short ultimate 
branchlets Laurencia (in part) 
96. Thalli creeping, with few very short 
ultimate branchlets 
Chondria (repens) 
97. Thalli minute, mostly under 2 mm. high 
98 
97. Thalli larger, 1-3 cm. high. . . Hypnea 
98. Growing points without trichoblasts . . 
Gelidiella (tenuissima) 
98. Growing points provided with short 
trichoblasts Chondria (in part) 
99- Individual filaments (trichomes) taper- 
ing from base to apex 100 
99- Individual filaments not tapered, of ap- 
proximately equal diameter throughout 
101 
100. With intercalary heterocysts . Calothrix 
100. With basal heterocysts Rivularia 
101. Filaments epiphytic, erect, attached by 
a single, modified basal cell 
Erythrotrichia 
101. Filaments epiphytic or saxicolous, but 
entangled and without any evident 
specialized basal attachment cell on 
individual filaments .102 
102. Filaments with false branching by pro- 
trusion of trichomes through breaks in 
the sheath; heterocysts present or ab- 
sent. ....103 
102. Individual filaments without false 
branching 104 
103. Heterccysts present Scytonema 
103. Heterocysts not present. . Plectonema 
104. Heterocysts present. Hormothamnion 
104. Heterocysts not present 103 
105. Without a sheath around the uniseriate 
filament 106 
105. Uniseriate filaments surrounded by a 
sheath 109 
106. Filaments straight or curved, but not 
spirally coiled 107 
106. Filaments spirally coiled. . . . Spirulina 
107. Cells very short, less than half as long 
as broad Oscillatoria 
107. Cells not very short, generally longer 
than broad; filaments generally over 20 
/d in diameter 108 
108. Filaments 20-30 id in diameter. ....... 
Rhizoclonium 
108. Filaments 60-90 /x in diameter 
Chaetomorpha 
109- Cells very short, less than half as long 
as broad 110 
109. Cell length about equal to or greater 
than breadth Ill 
110. Sheaths distinct, firm; trichomes single 
within the sheath Lyngbya 
110. Sheaths more or less mucous, diffluent; 
trichomes several within the sheath. . . 
Hydrocoleum 
111. Trichomes single within the sheath. . . 
112 
111. Trichomes many within the sheath, at 
least in older parts 115 
112. Trichomes 3 m °r less in diameter. .113 
