Dichothrix gypsophila ( Kuetz. ) Bornet & Flahault 1886, p. 377 



PI. 133, Figs. 1, 2 



Either solitary among other algae or forming tufts and expanded 

 strata, frequently encrusted with calcium carbonate; filaments re- 

 peatedly branched, the branches parallel with the principal trichome 

 and inclosed in the same sheath with it for a considerable distance; 

 vegetative cells shorter than wide at the base and with convex walls, 

 longer than wide toward the distal end and cylindrical without 

 constrictions at the cross walls, 6-8/x in diameter in the basal portion 

 of the trichome; heterocysts subglobose or hemispherical, 10-12/x 

 in diameter; sheaths lamellated, at first close, then becoming funnel- 

 shaped toward the distal end; filament (12)-15-18fi wide at the 

 base; penicillate tufts as long as 2 mm. 



This species varies in its sheath characters, apparently^ for authen- 

 tically named material which was compared with Wisconsin plants 

 shows both close, tapering sheaths as well as flaring, funnel-forming 

 sheaths. It should be compared with D. Hosfordii, a much larger 

 plant with sheaths bulbous at the base. 



Forming tufts of filaments entangled among other filamentous 

 algae in shallow water at the margin of marshy lakes. Wis. 



Dichothrix Hosfordii ( Wolle) Bornet in Setchell 1896a, p. 190 



PI. 133, Figs. 3, 4 



Plants penicillate tufts of stout, dichotomously branched filaments, 

 20-28;Li in diameter at the base; vegetative cells much shorter than 

 their diameter, lO-lS^u, in diameter at the base, 3-5/x long, becoming 

 cylindrical and several times their width in length in the distal 

 region, which tapers to a hair-like point; heterocyst a short, broad 

 cone, or hemispherical, olive or blue-green, 15-18/j. in diameter; 

 sheaths lamellated and bulbous at the base, several trichomes within 

 a sheath, the branches appressed for some distance, then emerging 

 in their own sheath. 



This species is more common in our collections than D. gypsophila. 

 It occurs among other algae in a number of both hard and soft 

 water lakes. The greater size and the bulbous-inflated sheaths help 

 to identify it. Mich., Wis. 



Dichothrix Orsiniana ( Kuetz. ) Bornet & Flahault 1886, p. 376 



PI. 133, Figs. 5, 6 



Gelatinous, penicillate tufts, composed of slender trichomes in 



close and thick, lamellated, tapering sheaths; filaments branching 



freely, the branches extending for most of their length within the 



sheath of the principal trichome; trichomes subcylindric below, 



[555] 



