

BLUE-GREEN ALG^ (CYANOPHYCE^) 205 



of the Antarctic continent. The Blue-green Algze are either uni- 

 cellular (Chroococcus, Fig. 112, A), colonial (Glceocapsa, Fig. H2,C), 

 or filamentous (Oscillatoria ; Lyngbya, Fig. 112, F; Nostoc, 

 Fig. 112, B). The cells possess either no nucleus in the ordinary 

 sense, or one of very simple construction, and are in nearly every 

 case devoid of a definite chloroplast. The cells or filaments, as 

 the case may be, are often contained in large numbers in mucila- 

 ginous envelopes (e.g. Glceocapsa, Nostoc), to which maybe partly 



FIG. in. Red Algae. A, Carrageen (Chondrus crispus), the dark 

 patches being due to groups of carpospores (p. 228) . B, Corallina. 

 C, Apex of a branch of Ceramium (after Kiitzing), with groups of 

 tetraspores (shown black). 



attributed the capacity of many species to survive considerable 

 periods of drought. 



Common members of the group are : Glceocapsa forming exten- 

 sive gelatinous coverings on damp substrata and, under the 

 microscope, resembling a blue-green Palmella-stage (Fig. 112, C) ; 

 Oscillatoria and Lyngbya, whose undifferentiated and unbranched 

 filaments of discoid cells (Fig. 112, F) occur as sheets or bundles 

 in freshwater pools, on moist stonework, etc. ; Tolypothrix, a 

 branched filamentous form, usually aquatic (Fig. 112, E) ; and 

 the mainly terrestrial Nostoc, the species of which take the form 



