156 FRESH-WATER BIOLOGY 



1 55 fas 2 ) J 37> 174) Reproduction by the formation of zoospores only, or by 



isogametes Family PROTOCOCCACEAE . . 156 



156 (161, 168) Cells spherical 157 



J S7 (158) Chromatophores many, parietal Botrydiopsis Borzi. 



Chromatophores without pyrenoids; zoospores amoeboid, with 

 a single cilium, a pigment spot, and one (sometimes two) chroma- 

 tophores; frequently they germinate within the mother-membrane 

 without a motile period. 



FIG. 189. Botrydiopsis eriensis Snow. a. vegetative cell; b. zoospores. 

 X 580. (Original.) 



158 (157) Chromatophore single 159 



159 (160) Chromatophore parietal Chlorococcum Fries. 



Chromatophore with a circular opening and a pyrenoid; zoospores 

 oval, with two cilia, a pyrenoid, and a pigment spot. Aplanospores 

 may form from non-liberated zoospores. An undescribed form 

 which greatly resembles Chlorococcum has isogametes. It should be 

 placed in a different genus. 



FIG. 190. Chlorococcum infusionum Rabenhorst. a. vegetative cell. 

 b. zoospores. X 625. (Original.) 



1 60 (159) Chromatophore central with radiating strands. 



Radiosphaera Snow. 



Except for the nature of the Chromatophore this genus 

 resembles Chlorococcum, but at the center is a pyrenoid 

 from which the chromatophore radiates. Zoospores 

 with two cilia and a pigment spot are formed. 



FIG. 191. Radiosphaera sp. Snow. a. vegetative cell; 

 b. zoospores. X 580. (Original.) 



161(156,168) Cells more or less irregular, elongated, or tubular. ... 162 



162 (163) Cells free, more or less inflated or tubular, usually with a long, 

 colorless cylindrical portion. Protosiphon Klebs. 



Chromatophore a parietal, net-like layer, with pyrenoids. Under conditions threatening 

 drought, red resting spores are formed. In absence of light or increase of water bi-ciliated 

 zoospores are formed which on coming to rest produce spherical cells, or they may copulate and 

 produce star-shaped zygospores. 



FIG. 193. Protosiphon botryoides Klebs. X 75- (After Klebs.) 



163 (162) Cells endophytic, rarely free, irregular, often with cellulose pro- 

 jections 164 



