224 FRESH-WATER ALG^ OF THE UNITED STATES. 



ZYGNEMA PURPUREUM, Wolle. 



Diameter of vegetative filaments, 20-25 // ; cells one, or 

 more rarely two diameters in length. Primarily yellowish 

 green, but soon changes to a dark purple ; fruiting filaments 

 more or less geniculated ; zygospores spherical ; spore-bear- 

 ing cells slightly, or not at all swollen. 



Common in ponds of New Jersey, floating in large, loosely 

 interwoven masses, but very rarely in perfect fruit. Found 

 it very abundant also, in Florida; ditches in the Tocoi 

 marshes, near St. Augustine, literally covered with it, as a 

 smooth, glistening dark purple mantle ; frequent in perfect 

 fruit. The chlorophyl is usually more or less centrally con- 

 tracted in each cell. There is no evidence of twin nuclei, a 

 fact which, with the color and the geniculate feature of the 

 filaments, make distinct specific characters. 



Plate CXLIV, figs. 3-7, sterile and fertile filaments. 



ZYGNEMA CRUCIATUM, Ag. 



Diameter of vegetative filaments, 35-50 yw ; cells one half 

 to twice as long as wide. Fructiferous cells not swollen ; 

 copulation scalariform ; zygospores spherical, dark brown ; 

 sporoderm finely punctate. 



Mostly in stagnant waters. 



Mainly separated from larger form of Z. stellium by the 

 spherical spores. 



Syn. Conjugata cruciata, Vauch. ; Tyndaridea cruciata, Hass. ; 

 Conferva bipunctata, Dillw. ; Zygnema Dillwyni, Kg. 



Plate CXLIY, fig. 1, an early stage of spore-formation by 

 the union of the two stellate nuclei in a cell ; fig. 2, fertile 

 and sterile cells on the same filaments. 



ZYGNEMA ANOMALUM, (Hass.) Kg. 



Diameter of vegetative filaments, about 25 /* ; surrounded 

 by a colorless gelatinous sheath, often twice the diameter of 

 the vegetative cells; sometimes even, sometimes much in- 

 flated, constricted at the joints. Cells equal or nearly twice 

 as long as wide. Zygospores globose, olivaceous ; sporoderm 

 distinctly punctate. 

 Syn. Tyndaridea lutescens, Hass. ; Tyndaridea anomala, Hass. 



Var. CRASSUM, Wolle. 



Diameter of vegetative filaments, 40-44 fa without sheath ; 

 with it 63 /* more or less ; cells primarily 3-4 times longer 

 than broad ; after division 1-1 J times longer. Cells, and 

 sheath of shorter cells, somewhat swollen. 



