. Fresh-water biology. Freshwater biology. THE FRESH-WATER ALGAE 159 178 (179, 180, 181) Cells spherical Coelastrum Nageli. t8K;''^«:; Cells spherical or slightly angled; chromatophore a hollow sphere, open at one side, with a pyrenoid opposite the opening. , Coelastrum occurs in all bodies of water, and is found in the plankton. p It is very resistant to unfavorable conditions, persisting long after most other algae have perished. Fig. 201. Coelastrum sphaericum NtigeU. X Ciao. (Original.) 179 (178, 180, 181) Cells cordate or reniform Sorastrum Kiitzing. Chloroplast parietal, with a single py
. Fresh-water biology. Freshwater biology. THE FRESH-WATER ALGAE 159 178 (179, 180, 181) Cells spherical Coelastrum Nageli. t8K;''^«:; Cells spherical or slightly angled; chromatophore a hollow sphere, open at one side, with a pyrenoid opposite the opening. , Coelastrum occurs in all bodies of water, and is found in the plankton. p It is very resistant to unfavorable conditions, persisting long after most other algae have perished. Fig. 201. Coelastrum sphaericum NtigeU. X Ciao. (Original.) 179 (178, 180, 181) Cells cordate or reniform Sorastrum Kiitzing. Chloroplast parietal, with a single pyrenoid. Cells on short stalks radiating from a gelatinous center, but both center and stalks usually hidden by the cells. A new coenobium from each cell. Sorastrum is of less frequent occurrence than most of the other members of the Coelastraceae, but is found in most localities where they are found, especially in the sediment at the bottom of ponds, and occasionally in the plankton. Fig. 202. Sorastrum spinulosum N^gell. X 600. (Original.) ,180 (178, 179, 181) Cells crescent-shaped, points turned outward. Selenastrum Reinsch. Cells acutely pointed. Chromatophore parietal, with no pyrenoid. By many this is placed near to Ankistrodesmus rather than with the Coelastraceae. Fig. 203. Selenastrum gracile Reinsch. X 565. (Original.). 181 (178, 179, 180) Cells club-shaped or elongated, forming a star. Actinastrum Lagerheim. Rays pointed, each ray composed of a single cell, all of which unite at the center. Chromatophore single, parietal, often not extending to the ends. Fig. 204. Actinastrum hantzschii Lagerheim. X 550. (Original.) 182 (177, 186) Cells in one plane 183 i83_(i84, 185) Cells four, eight, or sixteen in one or two parallel or zigzag rows Scenedesmus Meyen. The cells oval or pointed, the membrane either smooth or furnished with distinct spines at the ends. Chromatophore single, parietal, with an opening at one side and a pyrenoid. This is one of the most common and the b
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