WISCONSIN PHJTOPLANKTON 185 



ZYGNEMA PECTINATUM (Vaucher) C. A. Agardh. PI. 51, Fig. 2. 



Synop. algarum Scand. 102. 1817; DeBary, Unters. u. d. Fam. d. Conjugates 

 77, pi. 1, figs. 15-19. 1858. 



Vegetative cells 1-3 times as broad as long. Zygospore formed in 

 conjugation tube, with rounded ends. Middle layer of zygote wall 

 brown and scrobiculate. (Tychoplanktont). 



Vegetative cells 30-40 /* broad. Zygote 35-^0 /x broad. 



Oconomowoc (rrr). 



SPIKOGYBA Link 1820. 



Cells cylindrical, with end walls a fiat plane or replicate; united to 

 form simple filaments that may be attached by a modification of the 

 terminal cell into holdfasts. Length of cells slightly greater than to 

 several times the breadth. Chloroplasts one to several, parietal, in 

 long ribbons that extend from end to end in the cell and generally 

 make several spiral turns. Nucleus single, moored in the center of the 

 central vacuole by cytoplasmic strands running to the pyrenoids. Chlor- 

 oplasts with several pyrenoids that are generally in a single median row. 



Conjugation sealariform or lateral, with zygote formation in game- 

 tangia and never in the tube. Zygote spherical, ellipsoid, or cylindri- 

 cal with rounded ends. Middle layer of zygote hyaline or colored, 

 smooth or sculptured. 



SPIROGYRA PORTICALIS (Miiller) Cleve. PI. 51, Fig. 3. 



Nova Acta Reg. Soc. Sci. Upsaliensis 3, Ser., 6: No. 11, 22, pi. 5, figs. 8-13. 

 1S68. 



Length of vegetative cells 2-6 times the breadth. Cells with plane 

 cross walls and containing a single chloroplast that makes 3-5 turns and 

 contains numerous conspicuous pyrenoids. Gametangia but little swol- 

 len when zygospore is mature. Zygospores broadly ovoid to sub-cylin- 

 drical, with a yellow membrane when mature. (Tychoplanktont). 



Diam. cells 30-50 p. Diam. zygospores 40-50 p.. 



Mendota (rrr). 



