arranged filaments radiating from a common center and tapering 

 from a basal heterocyst to a very fine point; colonial mucilage 

 bounded by a leathery integument; cells short, barrel-shaped or 

 quadrate below, becoming cylindrical in the distal portion, 4-7/a in 

 diameter, 8-12yu, long; heterocysts spherical or ovate, 8-ll-(15)/>i in 

 diameter; gonidia cyhndrical with broadly rounding poles, the 

 membrane thick and sheathed, 10-15/x, in diameter, up to 400/;, long. 



This species is attached throughout its entire development, rarely 

 or only incidentally becoming free-floating. In suitable hard water 

 habitats its brown or olive globular colonies are thickly clustered 

 and sometimes completely coat over submerged aquatics such as 

 Potamogeton spp. and Ceratophyllum demersum. Because of the 

 firm texture of the colonial mucilage and the compact arrangement 

 of the filaments, the species may be confused easily with Rivularia 

 when the plants are young, before gonidia have developed. 



Common in many hard or semi-hard water lakes and streams. 

 Mich., Wis. 



SACCONEMA Borzi 1882, pp. 282, 298 

 Colonial mass amorphous or somewhat tubercular, the mucilage 

 soft and irregularly lobed and folded, and lamellate; trichomes 

 radiating irregularly, 2 or several within the same sheath, which is 

 wide, lamellate, and expanded at the extremities; heterocyst and 

 akinetes basal, the trichome tapering to fine hair-like points; plants 

 attached to stones and other submerged substrates; one species. 



Sacconenia rupestre Borzi 1882, pp. 282, 298 

 PL 136, Figs. 1, 2 

 Characteristics as described for the genus; trichomes 8-10/* in 

 diameter at the base; heterocysts globose or compressed-spheroidal; 

 akinetes globose, 15/i, in diameter, with a granulose wall. 



On stones from a depth of 20 feet, Douglas Lake, Michigan. 



CLASS CHLOROBACTERIACEAE 



In this group of the Cyanophyta are classified minute, bacteria- 

 like organisms of uncertain position which are weakly pigmented. 

 The cells are spherical or bacilliform and are arranged to form 

 amorphous, gelatinous colonies in which the cells have no definite 

 arrangement, or the cells may form false filaments or reticulate 

 associations. The colonies may vary greatly in size from 4-celled 

 aggregates to gelatinous masses containing hundreds of individuals. 

 See p. 36 in connection with chlorophyll tests involving a member 

 of this class. 



[560] 



