fertile cells cylindric. Zygospores ellipsoid or cylindric-ellipsoid, not 

 compressed; spore walls smooth, becoming yellow-brown in age; 

 100-140/x in diameter, 160-255^1^ long. 



This species is readily differentiated from other large forms in 

 our collections (S. crassa and S. maxima) by the large ellipsoid 

 spores with smooth walls. In our region it has not been collected in 

 pure growths as have many other species of the genus. 



Among other filamentous algae in shallow water. Mich., Wis. 



Spirogyra fallax ( Hansg. ) Wille 1900a, p. 16 

 PI. 77, Fig. 10 

 Filaments of rather slender cylindrical cells, 33-45/1. in diameter 

 and up to 8 times the diameter in length, with replicate (rarely 

 plane) end walls; chloroplasts 3-5, making V2 to lio turns (sometimes 

 nearly straight ) . Conjugation scalariform, the tubes short but formed 

 from both gametangia; fertile cells inflated (shortened). Zygospores 

 ellipsoid; wall layers smooth; 45-60ja in diameter. 

 Mich. 



Spirogyra Farlowii Transeau 1914, p. 291 

 Filaments of rather long cylindrical cells 24-30/x in diameter and 

 up to 180/x long, with replicate end walls; chloroplast solitary, 

 making 21/0 to 6 turns. Conjugation scalariform by tubes from both 

 gametangia; fertile cells fusiform, inflated. Zygospores ellipsoid; 

 median spore wall smooth; 32-45/x in diameter, 48-93|U long. 

 Mich. 



Spirogyra flavescens (Hass.) Kuetzing 1849, p. 438 

 Filaments of slender cells, 11-13/a in diameter and up to 4 times 

 the diameter in length, with plane end walls; chloroplast solitary, 

 making 1 to 2 turns. Conjugation scalariform by tubes from both 

 gametangia, the fertile cells inflated. Zygospores ovate to cylindric- 

 ovate; median spore wall smooth; 20/x in diameter, up to 30/i, long. 

 Mich. 



Spirogyra fluviatilis Hilse in Rabenhorst 



1864-1868, Algen No. 1476 

 PI. 73, Figs. 4, 5 

 Filaments of rather stout cells, (30)-36-40-(45)/x in diameter and 

 5-6 times the diameter in length, with plane end walls; chloroplasts 

 3-5, making IK to 21/2 turns. Conjugation scalariform by tubes from 

 both gametangia, fertile cells becoming inflated. Zygospores ovate; 

 median spore wall wrinkled and irregularly pitted; 42-44- (65) /a in 

 diameter, 59-77- ( 110)/x long. 



In pooled streams; common in lakes and ponds. Mich., Wis. 



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