212 FRESH-WATER ALG^E OF THE UNITED STATES. 



fruiting cells swollen only on the side of conjugation, the 

 opposite side straight. Zygospores oval, turning yellow at 

 maturity, about twice as long as wide. 



Syn. Zygnema gracile, Hass. 



This form has been erroneously connected with 8. flaves- 

 cens. It is distinct in size, and in spore-bearing cells, which 

 are inflated on one side only, not on two sides. 



The figures are from specimens collected in Michigan. 



Plate CXXXIV, figs. 5-7, conjugation scalariform, and 

 lateral ; fruits also without conjugation ; also sterile filament. 



SPIROGYRA VARIANS, (Hass.) Kg. 



Diameter of vegetative filaments, 25-33 yu; cells H-2i 

 times as long as wide; spiral single, with margins more or 

 less dentate, describing l*-3 turns; cells bearing spores 

 much swollen on the conjugating side, straight on the outer 

 side. Zygospores oval or elliptic, li-2 times longer than 

 wide, often appearing polymorphous, changing with the 

 position they have in the cell. 



Syn. Zygnema varians, Hass.; Ithynchonema Woodsii, Kg.; Zyg- 

 nema abbreviatum, Hass.; 8. arcta, Kg.; S. nodosa, Kg.; 

 8. ventricosa, Kg. 



Of all the species of this genus this appears most poly- 

 morphous, and in consequence has given rise to various 

 terms descriptive of conditions in which it was found by 

 different collectors, and by the same under different circum- 

 stances; frequently inflated cells are observed in longer or 

 shorter series; these no doubt gave rise to such names as 

 nodosa and ventricosa. Often the cells are very short, hence 

 abbreviatum. 



The peculiar one-sided swelling does not appear to have 

 been noticed by Vaucher, and probably did not exist in the 

 plant he saw and described as 8. condensata ; hence there 

 appears no good reason for calling 8. varians a synonym for 

 S. condensata. 



Most abundant in stagnant pools adjoining mountain 

 streamlets. 



Plate CXXXIV, figs. 8-13, sterile filament ; fruiting fila- 

 ments, cells inflated without conjugation ; and early stage 

 of conjugation. 



SPIROGYRA SUBSALSA, Kg. 



Diameter of vegetative filament, 22-25 jw; cells 1-1? 

 times longer than wide; single spiral, describing 1^-2-3 

 turns in cell, Zygospore ovoid, slightly longer than the 



