222 FRESH-WATER ALG^ OF THE UNITED STATES. 



Genus 71, SIBOGONIUM, Kg. 



Filamentous, composed of a series of cells with parietal longi- 

 tudinal or somewhat spiral chlorophyl bands. Fructifying cells 

 diverse, arising by unequal division of the cells of the filaments, 

 bending knee-like towards each other and growing together ; 

 united at the point of adnation ; zygospore elliptic. 



The sterile cells, with the chlorophyl bands, resemble those of 

 Spirogyra, but differ in the genuflexuous conjugation. 



SlROGONIUM STICTICUM, Kg. 



Diameter of vegetative filaments, 45-50 /< ; cells 2-4 times 

 longer than broad ; 3-4 chlorophyl bands ; zygospores 

 broadly elliptical ; spore-bearing cells more or less swollen. 



Syn. Sirogonium breviarticulatum, Kg. ; Sirogonium Braunii, Kg. ; 

 Conferva stictica, Eng. Bot. ; Zygnema curvatum, Ag. ; 

 Choaspes serpentina, Gray. 



Ponds, Florida. Have seen no specimens found north of 

 the Gulf States. 



Plate CXLI, figs. 8-10, copulating filaments, with two 

 spores matured and one forming. 



Genus 72, ZYGNEMA, Kg. 



Cells with two axile many -rayed chlorophyl bodies standing 

 near the central cell nucleus, each containing a starch-granule. 

 Copulation scalariform or lateral ; zygospore in one of the united 

 cells, the same as in Spirogyra. Intermedial membrane of the 

 sporoderm scrobiculate, even, or punctate. Cells having densely 

 granular contents, including the two starch granules and often 

 surrounded by a cytioderm of several layers, are supposed to be 

 resting cells. 



A. The intermedial membrane of spores smooth. 



ZYGNEMA LEIOSPERMUM, D. By. 



Diameter of vegetative filaments, 20-22 /* ; sterile cells 

 twice as long as wide ; fructiferous cells usually shorter ; 

 equal to the diameter, somewhat swollen. Zygospores orbi- 

 cular or broadly oval. 

 Small pools. 



Plate CXLIII, figs. 1, 2, 3, parts of two sterile filaments 

 and one fertile. 



