FISCHERELLA (Bornet & Flahault) Gomont 1895, p. 52 



A branched and sheathed filament with a stouter, prostrate portion 

 giving rise to vertically elongate, much narrower, curved or straight 

 branches in which 1 or more hormogonia are formed; cells sub- 

 globose, quadrate, or cylindrical, usually loosely arranged in 1 to 

 several series in the principal filament, in a single series only in the 

 branches; hormogonia with cells closely adjoined and usually in- 

 creasing in diameter toward the apices; heterocysts globose, barrel- 

 shaped, or quadrate; sheaths either colorless or brownish, homo- 

 geneous or lamellated. 



This genus is considered by some to be unseparable from Stigo- 

 nema and is, therefore, often included with it as a subgenus. When 

 given genus rank it is differentiated principally by the unilateral 

 arrangement of the branches, which are distinctly smaller than the 

 main filament, and also by the habit of forming hormogonia in 

 the apices of the branches. 



Key to the Species 



Main filament mostly uniseriate F. ambigua 



Main filament multiseriate F. muscicola 



Fischerella ambigua ( Naeg. ) Gomont 1895, p. 49 



Plant mass consisting of prostrate mats of interwoven filaments 

 from which vertical fascicles arise; filaments 6-9/x in diameter, 

 giving rise to unilateral branches, which are grouped; sheaths 

 colorless when young, becoming brownish; cells 2-3/a in diameter, 

 ovate or subglobular to quadrate in the main axis, rectangular in 

 the branches, 4-6 times longer than wide; heterocysts cylindrical. 



On moist soil. Mich. 



Fischerella muscicola (Borzi) Gomont 1895, p. 52 

 PI. 130, Figs. 7, 8 



Plant mass consisting of prostrate, irregularly spreading filaments, 

 containing several series of cells, from which mostly unilateral and 

 uniseriate branches arise; cells quadrate or subglobose in the main 

 axis; branches 4-6/i, in diameter, developing hormogonia up to 100/x 

 in length; heterocysts globular or barrel-shaped, about the size of 

 the vegetative cells; sheaths colorless or brownish, without lamella- 

 tions; filaments 10-14;u in diameter. 



In shallow water at the margin of ponds among filamentous algae 

 and larger vegetation. Mich., Wis. 



[549] 



