THE FRESH-WATER ALGAE 



217 (198, 218) Plants of unbranched, free-swimming, more or less gelatinous 

 filaments, the cells very long; chlorophyll parietal and sur- 

 rounding a number of large conspicuous vacuoles which 

 show as a row of lighter areas; pyrenoids numerous. Re- 

 production by heterogametes. 



Family SPHAEROPLEACEAE. 

 Only one genus known Sphaeroplea Agardh. 



FIG. 224. Sphaeroplea annulina Agardh. 

 (After Rauwenhoff.) 



X 1133- 



Cells cylindrical, tapering; length 

 eight to twenty times the breadth, 

 several nuclei present. Oogonia and 

 antheridia formed from vegetative cells, 

 the oogonia containing many oospheres, 

 and the antheridia a very large number 

 of antherozoids with two cilia; these are 

 liberated through holes in the mem- 

 brane and enter the oogonia through 

 similar holes; the oo spores are red and 

 have a thick, rough membrane. On 

 germination each produces one to eight 

 zoospores with a pigment spot and 

 two cilia. Spores may be produced 

 parthenogenetically . 



218 (198, 217) Plants of unbranched, more or less gelatinous, filaments, 

 attached in early stages; cells short, cylindrical, or swollen; 

 chromatophore single, parietal, with one pyrenoid. Repro- 

 duction by means of zoospores with two cilia and by hetero- 

 gametes Family CYLINDROCAPSACEAE. 



Only one genus known Cylindrocapsa Reinsch. 



Reproduction asexual and sexual; asex- 

 ual, by zoospores and akinetes; sexual, by 

 means of oogonia, each with one oospore, 

 and antheridia, each with two anthero- 

 zoids; oospore red in color. 



This is a very rare alga though it is 

 reported by Collins as occurring in Massa- 

 chusetts and by Wolle as occurring from 

 New York to Florida. 



FIG. 225. Cylindrocapsa involuta Reinsch. 

 a. vegetative filament; b. formation of anthero- 

 zoids; c. oogonium with antherozoids. X 575- 

 (After Cienkowski.) 



219 (197) Filaments coarser, mostly branched 220 



220 (233) Chromatophore with irregular, linear, or net-like perforations. 221 



221 (230) Zoospores biciliate Family CLADOPHORACEAE . . 222 



Filaments mostly branched, harsh to the touch, generally attached; chromatophore parietal, 

 with irregular, net-like perforations; contents granular; numerous pyrenoids. Nuclei many. 



222 (223) Filaments never branched except at the attachment. 



Chaetomorpha Kiitzing. 



Filaments attached by a branched, rhizoid-like organ. Reproduction by means of zoospores. 

 The species of this genus are mostly marine. 



223 (222) Filaments usually branched 224 



