184 WISCONSIN PHJTOPLANKTON 



either stellate or laminate and axial or parietal. Chloroplasts with one 

 to many pyrenoids. 



Asexual reproduction by vegetative cell division or metamorphosis 

 of cell contents into a single large aplanospore. 



Sexual reproduction isogamous, by metamorphosis of all or a part 

 of the cell contents into an aplanogamete which fuses with an aplano- 

 gamete from the same or another filament. Zygote with 2-3 layers, 

 sometimes germinating immediately but usually after a period of rest. 



KEY TO THE GENERA. 



Cbloroplast stellate ZYGNEMA 



Cbloroplast a longitudinal band. 



Chloroplast axial MOTJGEOTIA 



Chloroplast parietal SPIBOGYRA 



MOUGEOTIA C. A. Agardh 1824. 



Cells cylindrical, generally several times as long as broad. Chloro- 

 plast single, forming an axial plate extending the whole length of the 

 cell and generally with several pyrenoids. 



Conjugation generally scalariform and with the zygote formed in the 

 conjugation tube. Zygote at times occupying the median portion of 

 male and female garnetangia as well as conjugation tube. Wall of 

 zygote of two layers the inner smooth, the outer smooth or sculptured, 

 hyaline or colored. 



MOUGEOTIA VIRIDIS (Kiitzing) Wittrock. PI. 51, Fig. 1. 



Bib, Kgl. ST. Vet.-Ak. Handl. 1, No. 1: 39. 1872. 



Staurospermum viride Kiitzing. Cooke, Brit. Freshw. Algae 107, pi. 44, 

 figs. 2a-2c. 1882. 



Cells 4-10 times as long as broad. Zygospores normally bounded by 

 four cells, quadrangular, with concave sides and truncate corners. 

 (Tychoplanktont) . 



Cells 6-8 fji broad. Zygotes 22-32 /* broad. 



Okauchee (rrr). 



ZYGNEMA C. A. Agardh 1817. 



Cells cylindrical, rarely more than twice as broad as long. Filaments 

 with a terminal cell at times modified to form a holdfast. Cells with 

 one nucleus and two axial stellate chloroplasts each of which contain 

 a single pyrenoid. Conjugation lateral or scalariform, with a forma- 

 tion of zygospores in the conjugation tube or the gametangia. Zygotes 

 spherical to ellipsoid, wall with three layers. 



