No. IO.] FRESH- WATER ALG^E. 43 



According to West the forms with four cilia should be 

 named Carteria, Fig. 290. Both the two- and the four-ciliate 

 forms are common in our waters. 



Sphserella Sommerfeldt ( Chlamydococcus A. Br.; 

 Haematococcus Ag.). Like Chlamydomonas, except that 

 the cell walls are outstanding and joined to the cell contents by- 

 fine threads. There is always more or less red coloring matter 

 present. 



[S. lacustris (Girod.) Witter.] 



ORDER II. ULVALES. 



Thallus expanded and parenchymatous; attached when 

 young by rhizoids. Each cell is furnished with a single nucleus 

 and a parietal chloroplast, often quite large, containing one 

 pyrenoid. 



FAMILY I. ULVACE^E. 



Most of the genera of this family are inhabitants of salt 

 or brackish water. The thallus consists of an expanse of cells 

 arranged compactly with their longer axes at right angles to 

 the plane of the thallus ; either flat or, more rarely, tubular. 

 The cells are uninucleate, with a single parietal, often ragged, 

 chloroplast, containing one pyrenoid. 



Asexual reproduction by zoogonidia with 4 cilia, and by 

 gemmae. Sexual reproduction by isogamous gametes. The 

 contents of a vegetative cell divide into 8 (sometimes 4 or 16) 

 gametes, smaller than the zoogonidia, which are pear-shaped, 

 with a pigment spot and two long cilia. As a result of conjuga- 

 tion a rounded cell with two pigment spots and 4 cilia is 

 formed, which becomes a zygospore on losing its cilia. 



Enteromorpha Lk. Thallus tubular, membranaceous ; 

 at first fixed, then floating; sometimes branched. It is either 

 green or pale olive-colored. Reproduction as in the family. 

 Found in salt or fresh water. 



ORDER III. SCHIZOGONIALES. 



The thallus, often attached by rhizoids, is filamentous, 

 sometimes several filaments being joined laterally to form a flat 



