HOW TO KNOW THE FRESH-WATER ALGAE 



CO CD 



432a Cells arranged in rectilinear series to form a flat plate. Fig. 313. 

 MERISMOPEDIA 



Fig. 313. a, Mehsmopedia elegans 

 var. major G. M. Smith; b, M. giau- 

 ca (Ehr.) Naeg. 



There are several species on rec- 

 ord from the United States, differ- 

 entiated by cell shape, color, and 

 presence of vacuoles. The genus is 

 easily distinguishable by the definite 

 arrangement of the cells in rectilinear 

 series. M. convoiufa Breb. is an un- 

 common species which has relatively 

 large plates that are enrolled at the 

 margin. 



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Figure 313 



432b Cells not arranged in rectilinear series 



433 



433a Cells heart-shaped or round, occurring at the ends of radiating 



strands of mucilage (focus down into the colony and cut down 



illumination to detect presence of radiating strands). Fig. 314. 



GOMPHOSPHAER1A 



Fig. 314. a, Gomphosphaeria 

 aponina Kuetz.; b, G. lacustris 

 Chod. 



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°o<b 



■ 9?o 



y* 



Figure 314 



These plants are characterized 

 by having cells in globular colo- 

 nies, closely or distantly arranged 

 at the ends of mucilaginous 

 strands that radiate from the cen- 

 ter of the thallus. G. lacustris 

 is frequently found in the euplank- 

 ton, whereas G. aponina occurs 

 mostly in the tychoplankton. 



433b Cells not at the ends of radiating strands 434 



179 



