OSCILLARIA. 315 



Our plants are nearest, var. duJeis, Kg. This diagnosis 

 includes also O. subsalsa, Ag. 



Plate CCVI, fig. 18, three parts of filaments from a gath- 

 ering made in Florida. 



OSCILLARIA NIGRA,- Vatich. 



Stratum more or less compact, ample, broad, mostly float- 

 ing, but frequent also on planks surrounding ponds and on 

 wet earth ; blackish green with long radii. Trichomes 

 straight or slightly curved, obtusely rounded, or more rarely 

 attenuated and sometimes bearded. Color of articulations 

 usually blackish blue, or dilute black ; length same as 

 breadth before division ; later I or as long as broad ; dis- 

 sepiments usually distinctly granular. 



Diameter of filaments, 9-10 yw. 



Plate CCVI, fig. 20, one of our most common forms. 



D. Articulations less than half as long as wide. 



OSCILLARIA PERCURSA, Kg. 



Trichomes solitary, scattered, or united, forming a thin 

 stratum, blue-green ; filaments radiating, straight or curved 

 at the apices ; dried filaments longitudinally plicate. Ar- 

 ticulations S-T as long as broad, here and there interrupted ; 

 dissepiments distinctly, ornately granular; cytioplasm di- 

 lute aeruginous. 



Diameter of cells, 15 JA, or slightly more or less. 



Plate CCVI, figs. 22, 23, four parts of trichomes from a 

 collection made in Central Florida. 



OSCILLARIA FRCELICHII, Kg. 



Stratum dark steel blue, or dark olive green, often elon- 

 gated, radiating, opaque, shining. Trichomes nearly 

 straight, even, not attenuated ; cells 2, 3, or 4 times shorter 

 than the diameter, after division 6-8 times shorter; aeru- 

 giuous, brown or green. 



A frequent and variable species. 



The following have been suggested as varieties : 



1. Var. genuina, Kirch. Stratum dark aeruginous; fila- 

 ments with ends nearly straight ; diameter 15-18 ^. 



2. --Var. viridis, Zeller. Stratum green, diameter 15 /*; 

 ends somewhat curved. 



3. --Var. dubia, Eab. Stratum bright aeruginous, diameter 

 of filaments, 13 //, ends straight. 



