372 BACTERIOLOGY 



CRENOTHRIX Cohn 



Beltrage Biol., I, 1875. 130. 



Filaments fixed to a substratum, usually thinner at the base than at the apex, 

 with thick sheaths. Cells cylindrical to flat, one-half the breadth of the 

 filament. Gonidia of two kinds : microgonidia, formed by a segmentation 

 of the vegetating cells, producing small spherical elements ; and macro- 

 gonidia, produced by the vegetating cells in the neighborhood of the 

 apex of the filament breaking up into larger oval elements. The gonidia 

 may either escape or germinate within the filaments. 



1. Crenothrix polyspora Cohn 



I.e. 



Long, stiff, unbranched filaments, composed of cells ; in the young filaments 

 a thin, and in the older filaments a thick sheath. There is often a depo- 

 sition of oxide of iron in the sheath, which stains the latter brown. Fila- 

 ments 1.5-5.2 ft broad. Vegetating cells one-half to four times the breadth 

 of the filaments. Gonidia formation as already described. Cultures on 

 artificial media not successful. According to Rbssler, organisms grow in 

 spring water containing fragments of sterilized brick, previously boiled in 

 water containing sulphate of iron. 



Habitat. Found in stagnant and running water, containing organic matter 

 and iron salts, as thick masses of a brownish or greenish color. 



CLADOTHRIX Cohn 



BeitrMge Biol., I, 1875. 



Filaments generally with delicate sheaths, often fixed and forming tufts. Cells 

 cylindrical. By intercalary growth a cell may break through the sheath 

 laterally, and by continuous growth produce a false dichotomous branch- 

 ing. Reproduction by motile gonidia (swarm spores), which bear a little 

 laterally to a pole, a bundle of flagella. 

 I. Filaments surrounded by thick gelatinous sheaths. 



1. Cladothrix natans (KUtzing) Migula. 

 II. Filaments with a delicate, or with a scarcely evident sheath. 



A. A ferruginous species, with an accumulation of hydrated oxide of iron 

 in the sheath. Do not grow in ordinary culture media. 



2. Cladothrix ochracea (KUtzing) Winogradsky. 



