HOW TO KNOW THE FRESH-WATER ALGAE 



204a With 2 disc-like chloroplasts. Fig. 144 PLEUROD1SCUS 



Fig. 144. Pleurodiscus purpureus 

 (Wolle) Lag., showing disc-like 

 chloroplasts. 



There is but one species of this 

 Figure 144 genus reported thus far from the 



United States. It is a plant easily 

 identified by its unique, plate-like chloroplasts and purple cell sap. 



204b With 1 band-like chloroplast. Fig. 145 MOUGEOTIA 



Fig. 145. a, Mougeofia gen- 

 uflexa ( D i 1 1 w . ) C. A. 



Agardh, showing genicu- 

 late or 'knee-bending' type 

 of conjugation and the 

 plate-like axial chloroplast; 

 b, M. elegantula Wittr., zy- 

 gospore with residues in 

 conjugation cells; c, M. sp., 



showing rhizoidal branch- 

 Figure 145 gg 



Like Spirogyra (Fig. 147) there are many species of Mougeotia 

 separable by zygospore shape and wall markings. Most species have 

 a relatively wide, band-like chloroplast containing a row of large 

 pyrenoids. The chloroplast (axial) is capable of rotating within the 

 cells so that the band, when seen on edge, appears as a narrow 

 ribbon. The shifting of the chloroplast is supposed to be a response 

 to the direction of more favorable illumination. 



205a (203) Chloroplasts in the form of spiral ribbons, with many pyre- 

 noids 206 



205b Chloroplasts axial bands or plates; pyrenoids 2 to several.. 208 



206a Cell wall densely and minutely granular. See Fig. 106 



GENICULARIA 



206b Cell wall smooth 207 



94 



