210 FRESH-WATER ALG^ OF THE UNITED STATES. 



turns ; fruiting cells shorter, slightly or not at all swollen. 

 Zygospores elliptic or cylindric-elliptic, ends rounded, yel- 

 low or orange when mature ; two or three times longer than 

 the diameter, 40-42 /*. Spore-membrane somewhat punctate 

 or scrobiculate. 



Syn. Spirogyra protecta, Wood. 



Not rare in ponds, East, West and South. 



B. Chlorophyl bands two or more; cells replicate at the ends. 



SPIROGYRA HASSALLII, (Jenn.) Petit. 



Diameter of filaments, 30-33 ^ ; cells 4-8 times longer than 

 wide; two spirals, rather large, lax, describing l-3 turns. 

 Fructiferous cells considerably inflated, 48-50 yu diameter ; 

 zygospores elliptic, ljj-3 times longer than the diameter, 

 measuring 42-48 //, and changing to yellow at maturity. 



Syn. Zygnema Hassallii, Jenn.; Rhynchonema Hassallii, Kg. 

 Only specimens identified, from Iowa. 



Plate CXXXIII, figs. 5-7, sterile filament, and lateral 

 copulation. 



SPIROGYRA INSIGNIS, (Hass.) Kg. 



Diameter of vegetative filaments, 36-42 ^ cells 4-12 

 times longer than wide ; three spirals, rarely two, describing 

 one to three turns. Cells bearing zygospores much swollen, 

 shorter than sterile cells. Spores elliptic, usually twice as 

 long as wide. Smaller axis about 28 yu. 



Beside the typical form, Kirchner has two varieties : 



Yar. BRAUNII, Eab. 



Cells 8-14 times as long as wide and two spirals ; and 



Yar. ELONGATA, Sur. 



Cells 5-12 times longer than broad, with 2-4 spirals. 



Syn. Zygnema insigne, Hass.; jRhynchonema Gallicum, Rivet. ; 

 Sirogonium retroversum, Wood. 



Inhabits small ponds, not frequent. Pennsylvania, New 

 Jersey to Florida, probably also westward. 



Plate CXXXIII, figs. 8, 9, sterile, and fruit-bearing 

 filaments. 



Plate CXLII, figs. 8, 9, parts of two filaments of 8. insigne, 

 with sterile cells, and others having the chlorophyl bands 

 destroyed, or transmuted into brown stellate forms. 



The physiological function of the stellate forms remains 

 undetermined. 



