No. IO.] FRESH-WATER ALG^. 69 



red when mature, the wall consisting of eight shields or plates. 

 The spermatozoids are spirally coiled. The oogonium is situ- 

 ated on a nodal cell from which five other cells grow and coil 

 around the oogonium, covering it closely. They divide once 

 or twice at the top, so that a crown of five or ten small cells 

 is formed. 



Description of Genera. 



Chara Vaill. The crown consists of five cells. The 

 stems are covered with a cortex. 

 C. sp. (?), Figs. 207-209. 



Nitella Ag. The crown consists of ten cells ; cortex 

 lacking. 



CLASS VI. PrL^OPHYCE^ (FUCOIDE^). 



The Algse of this class are almost exclusively salt-water 

 forms, known as the Brown Seaweeds, and include the most 

 highly developed of the Seaweeds. The vegetative cells are 

 uninucleate, and the chromatophores are distinctly brown. 



Asexual reproduction by means of motile cells or zoogonidia. 

 Sexual reproduction by isogamous or heterogamous gametes. 

 Copulation always takes place outside the plant, and the re- 

 sulting spore germinates directly. The motile cells always 

 possess two laterally placed cilia, one directly forward and the 

 other backward. 



While the class is made up mostly of marine plants, there is 

 one order that is found in fresh water. 



ORDER I. SYNGENETIC^. 



Exclusively fresh-water forms. Plants unicellular, solitary 

 or colonial, or multicellular ; free-swiming or motionless. The 

 cells are either naked or surrounded by a mucilaginous en- 

 velope. The cells are uninucleate, possess one or more pul- 

 sating vacuoles, one or two yellow or pale brown chromato- 

 phores, and occasionally pyrenoids. 



The order as thus defined includes about seven families. 

 But at least four of the seven are frequently classed with the 

 Flagellate Protozoa, and are described in the report upon the 

 Protozoa of our waters. These include the following genera : 



