158 



FRESH-WATER BIOLOGY 



171 (172, 173) Cells single, attached; oval, cylindrical, fusiform, or curved 



in shape. Chromatophore single and parietal. 



Characium A. Braun. 



Cells oval, pointed, or rounded at the ends, straight or curved, 

 sessile or stalked; attached to a substratum with or without a disc. 

 A pyrenoid usually present. Reproduction by zoospores which have 

 two cilia, a pyrenoid, and a pigment spot. 



Characium is very common on filamentous algae in all localities. The 

 shape is greatly influenced by the direction of the rays of light. 



FIG. 197. Characium longipes Rabenhorst. X 600. (Original.) 



172 (171, 173) Cells as in Characium, but the chlorophyll in many small, 



parietal discs. Characiopsis Borzi. 



The color is pale green. The zoospores are liberated by the wall of the 

 upper portion of the cell becoming dissolved. According to West, aplano- 

 spores may be formed, each of which becomes a gametangium and pro- 

 duces two or four gametes. Characiopsis is less frequent than Characium 

 but is found under the same conditions. 



FIG. 198. Characiopsis sp. X 600. (Original.) 



173 (171, 172) Cells attached, the new generation clustered at the free tip of 



the empty mother cell Sciadium A. Braun. 



Thallus of six to eight cylindrical cells, radiating from the tip of 

 a sessile, empty, cylindrical membrane; reproduction by six to eight 

 zoospores with two cilia each, which attach themselves at the tip of 

 the mother-membrane after the removal of a cap which liberates the 

 spores. 



Lemmermann unites Sciadium with Ophiocytium because rarely in 

 Ophiocytium the new generation develops from one end of the parent 

 cell, but the sessile characteristic and the basal disc of Sciadium 

 would seem to separate it from Ophiocytium where these characteris- 

 tics are not found. 



FIG. 199. Sciadium arbuscula A. Braun. X 600. (After Rabenhorst.) 



Reproduction by fission and by zoospores. 



Family CHLOROSPHAERACEAE. 

 Only one genus known Chlorosphaera Klebs. 



Cells usually in small cell complexes, originating by fission in 

 three directions. Chromatophore parietal, with a pyrenoid. Zoo- 

 spores usually eight in number, originating by successive internal 

 divisions. These have two cilia and a pigment spot. Each vegeta- 

 tive cell may become a resting spore. 



In its vegetative state Chlorosphaera resembles greatly Pleuro- 

 coccus -uulgaris, but it is aquatic, rather than aerial. It is a common 

 form in ponds and lakes, though rarely found in such quantities as 

 to be noticed, unless developed in culture. 



FIG. 200. Chlorosphaera lacustris Snow. X 585. (Original.) 



175 (90, 95, 131) Cells without a gelatinous envelop or stalks; closely united 



to form structures of definite shape (coenobia). ... 176 



176 (187) Coenobium usually a cluster of definite shape and structure, formed 



by the union of four, eight, sixteen, or thirty-two non- 

 motile cells arising from internal division. 



Family COELASTRACEAE. . . 177 



177 (182, 186) Cells radially placed or forming close clusters 178 



174 (132, 137, 



