HOW TO KNOW THE FRESH-WATER ALGAE 



424b Plant mass in the form of a cushion with cells arranged in ver- 



x- i 425 



tical rows wmM 



425a Cells surrounded by a sheath; plant mass thick, cartilaginous, 

 usually macroscopic. Fig. 309 CHONDROCYSTIS 



Fig. 309. Chondrocystis Schauinslandii 

 >. Lemm. 



mm&smm 



Figure 309 



,0 : QLJ-5^KfQ[j^^: This species forms extensive, cushion- 



Hlo^%V; ; :, like masses on exposed surfaces and 



are heavily encrusted with lime. The 

 colonial mass is inclosed by a tough 

 mucilage in which 'families' of cells 

 are surrounded by individual sheaths. 

 This is the only species in the genus 

 and seems to have been reported but a few times from the United 

 States. 



425b Cells not inclosed by a thick sheath; plant mass macroscopic . 426 



426a Plant mass forming a flat, encrusting layer; cells forming short, 

 erect unbranched moments. Fig. 310 PLEUROCAPSA 



Fig. 310. Pleurocapsa minor Hansg. 



In this genus the plant mass is essen- 

 tially filamentous but the cells are so close- 

 ly oppressed that the branching habit can- 

 not be determined easily without dissect- 

 ing. Encrusting thralli are produced with 

 some differentiation between the lower or 

 inner cells and those near the surface 

 which produce the endospores. 



Figure 310 



426b Plant mass cushion-like; cells forming erect branched filaments. 



Fig. 311 ONCOBYRSA 



Fig. 311. Oncobyrsa sp. a, habit of col- 

 ony; b, diagram of cell arrangement. 

 Oncofyyrsa rivularis is the most com- 

 mon species of this genus. It has com- 

 pactly arranged series of cells in which 

 the filamentous plan can be more easily 

 determined than in Pleurocapsa (Fig. 

 310). The thallus is a mound of cells, 

 encased in a tough mucilage on fila- 

 mentous algae. Although the general 

 habit is that of members of Chamaesiphonaceae, there have been no 

 endospores observed. 



177 



Figure 31 1 



