HOW TO KNOW THE FRESH-WATER ALGAE 



343a A colony of vase-shaped cones (loricas). 1 or 2 cones arising from 

 within the mouth of another and forming forked series. Fig. 243. 

 DINOBRYON 



Fig. 243. Dinobryon sertularia Ehr. 



There are several species of 

 this genus, all of which are char- 

 acterized by having the motile pro- 

 toplasts inclosed within colorless 

 envelopes. The envelopes are 

 usually contained 1 or 2 within 

 another so that branching chains 

 are formed. Some species occur 

 as solitary cells, however. The 

 genus is one which inhabits most- 

 ly hard water lakes in the eu- 

 plankton; sometimes are very 

 abundant and produce disagree- 

 able odors and tastes in reservoirs. 



Figure 243 



343b Cells solitary or arranged otherwise 344 



344a A unicell, consisting of a yellowish protoplast contained in a vase- 

 shaped envelope. See Fig. 243 DINOBRYON 



344b Cells shaped otherwise, solitary or colonial 345 



345a Cells solitary, colonial or filament- 

 ous; wall silicious and etched with 

 grooves or rows of dots which form 

 definite patterns; wall in 2 sec- 

 tions. 1 part forming a lid over a 

 slightly smaller one; oil drops usu- 

 ally conspicuous; solitary cells often showing a gliding or jerky 

 movement. DIATOMS. Fig. 243 1 /2 450 



Figure 243% 



345b Cells without silicious walls, so decorated; oil droplets lacking or 

 inconspicuous, not showing gliding movements; if motile, equipped 

 with flagella or moving by pseudopodia (amaeboid fashion) . . 346 



346a Unicellular, with flagella but usually not swimming 347 



346b Multicellular or colonial; motile or non-motile 365 



145 



