336 PHARMACEUTICAL BOTANY 
Nosroc.—Nostoc occurs on the damp ground bordering 
streams or in slow bodies of water as greenish or brownish, tough, 
gelatinous balls varying in size from a pea to a hen’s egg. When 
one of these masses is dissected and examined microscopically, it 
is seen to contain, imbedded in a gelatinous matrix, numerous 
serpentine filaments, composed of spherical or elliptical cells 
loosely attached to each other in chain-like fashion. Most of 
Fic. 244.—Blue-Green Algae. A, Anabena azolle; B, Anabaena inequalis; C, 
Cylindrospermum catenatum; h, heterocyst; s, spore; D-G, Rivularia bullata: D, Single 
filament; FE, F, hormogonia; G, formation of hormogonia; H, Merismopedia. (A, 
C, from Campbell’s “University Text-Book of Botany.” By permission of The 
Macmillan Co., Publishers; B, from “A Treatise on The British Freshwater Algae’’ 
by the late G. S. West; revised by F. E. Fritsch, Cambridge Univ. Press, 1927; 
D-G, after Bornet, from Engler and Prantl.) 
the cells are of the blue-green vegetative kind, but there occur at 
_ intervals larger cells, often devoid of protoplasm which are 
termed heterocysts. Frequently the filaments break apart on 
either side of the heterocyst, setting free segments of cells (hor- 
mogonia) which grow into new filaments. 
Crass II.—CuHLoropHyce#, THE GREEN ALGAE 
Green alge are unicellular (sometimes motile), filamentous, 
colonial, or sheet-like water plants characterized by the presence 
of solitary, or numerous chloroplasts in the cells which compose 
