WISCONSIN PHYTOPLANKTON 179 



ecus or lamellated. Cells containing a nucleus and one parietal, lami- 

 nate or cup-shaped chloroplast with one or more pyrenoids. 



Asexual reproduction by vegetative cell division, aplanospores or 

 biciliate zoospores. 



Sexual reproduction isogamous, by a fusion of bi- or tetraciliate zoo- 

 gametes. 



ULOTHEIX Kiitzing 1833. 



Filaments simple, free-floating or with the basal cell modified to form 

 a hold- fast. Cells cylindrical, with flattened end walls, united to form 

 simple filaments that are the same diameter throughout. Wall of cells 

 delicate or thick, homogeneous or lamellated, without a gelatinous outer 

 layer. Chloroplast single, parietal, laminate, with one or more pyre- 

 noids. Cells uninucleate. 



Asexual reproduction by the division of cell contents to form 1-32 

 aplanospores and bi- or tetraciliate zoospores. 



Sexual reproduction isogamous, by a fusion of biciliate zoogametes. 



KEY TO THE SPECIES. 



Filaments 11-45 M in diameter U. ZONATA 



Filaments 5-7 ft, in diameter U. SUBCONSTEICTA 



ULOTHRIX ZONATA (Weber & Mohr) Kiitzing. PI. 50, Fig. 6. 

 Flora 16: 519. 1833; Hazen, Mem. Torr. Bot. Cl. 11: 147, pi. 20, figs. 1-4. 1902. 



Filaments attached or free-floating and forming greenish masses. 

 Cells disciform to cylindrical, % to !-,' times as long as broad. End 

 walls of cells straight, side walls straigi.it or slightly convex in older 

 cells. Chloroplast forming a broad or narrow pariciai annular girdle 

 containing several pyrenoids. Wall of cell thick, generally homo- 

 geneous but at times lamellated in structure. (Tychoplanktont). 



Mature cells 11-45 p. in diameter. 



Mendota (rrr). 



ULOTHRIX SUBCONSTRICTA G. S. West. PI. 50, Figs. 4-5. 

 Jour, of Bot. 53: 82, figs. 6A-6c. 1915. 



Filaments free-floating, narrow, slightly constricted at cross walls of 

 cells, with or without a homogeneous gelatinous envelope. Cells elon- 

 gate, 2-6 times as long as broad, slightly inflated at the poles. Chloro- 

 plast single, parietal, laminate, with irregular edges and occupying 

 the median two thirds of the cell. With or without 1-2 pyrenoids. 

 Cell wall very delicate. (Facultative Planktont). 



