HOW TO KNOW THE FRESH-WATER ALGAE 



Figure 220 



311b Cells shaped differently 312 



312a Cells club-shaped or somewhat pear-shaped; walls in 2 sections, 



the upper lifting away to permit escape of spores. See Fig. 215. 



CHLOROTHEC1UM 



312b Cells spherical, fusiform, or ovoid; wall in 1 piece 313 



313a Stipe slender, thread-like, longer than the cell body. Fig. 220... 

 PERONIELLA 



Fig. 220. Peromelia Hyalothecae Gobi. 



Species of this genus occur solitarily 

 or in gregarious clusters on other algae, 

 or are attached in the mucilage of co- 

 lonial forms. The species illustrated 

 seems to occur no other place but on 

 the filamentous desmid, Hyalotheca. 

 Like other members of the Chrysophyta, 

 the chromatophores are not a grass- 

 green but a pale shade, and there are 

 usually refractive globules of oil or some 

 other kind of food reserve than starch. 



313b Stipe stouter, shorter than the cell body in length (or rarely equal- 

 ling it). See Fig. 217 CHARACIOPSIS 



314a (306) With 2 flagella of unequal length. Fig. 221 



CHLOHOCHHOMOJVAS 



(OCHROMONAS) 



Fig. 221. Chlorochromonas minuta Lewis. 



This rare species (probably referrable to 

 Ochromonas) is variable in shape from trun- 

 cately-oval to pear-shaped. Care must be 

 used in detecting the two flagella of unequal 

 length. Motile, pear-shaped cells in the mi- 

 croscope field, with yellowish chromatophores 

 should be examined for flagella characters. 

 Frequently the cells come to rest and attach 

 themselves to a substrate at the posterior end. 

 Only one species has been reported in the United States. 



314b Without flagella 315 



315a Cell wall smooth 316 



315b Cell wall sculptured or decorated, sometimes spiny 325 



316a Cells spherical, subglobose, or broadly ovate to subpyriform (pear- 

 shaped) 317 



316b Cells rectangular, cylindrical, or crescent-shaped 320 



Figure 221 



135 



