HOW TO KNOW THE FRESH-WATER ALGAE 



441a (427) Cells quadrangular, arranged in flat plates. Fig. 321 



TETRAPEDIA 



Fig. 321. Tetrapedia sp., diagram showing 

 arrangement of rectangular cells. 



Tetrapedia Reinschiana Arch, is a rare 

 plant that has quadrangular cells arranged 

 in multiples of 4 to form a flat rectangular 

 plate. One other species has been reported 

 from the United States, occurring in the plank- 

 ton. 



Figure 321 



441b Cells some other shape 



442 



442a Cells solitary or in colonies of few cells, up to 32 



443 



442b Cells numerous within a globular or amorphous gelatinous matrix. 



448 



443a Without a gelatinous sheath. Fig. 322 SYNECHOCOCCUS 



Fig. 322. Synechococcus aeruginosus 

 Naeg. 



This is a solitary unicell which does 

 not possess a gelatinous sheath. Cells 

 may be in pairs as a result of recent 

 fission. They are relatively large for 

 Cyanophyta (may be up to 35 microns 

 in length) and are often conspicuous in 

 the microscope mount because of their 

 briaht blue color. 



Figure 322 



443b With a gelatinous sheath (sometimes discerned with difficulty), 

 or inclosed by a gelatinous matrix 444 



183 



