142 



A quatic Organisms 



Crenothrix (Fig. 56 d, e and/) is a similar unbranched 

 sessile form which is distinguished by a widening of the 

 filaments toward the free end. This is caused by a 

 division of the cells in two or three planes within the 

 sheath of the filament, previous to spore formation. 

 Often by the germination of spores that have settled 

 upon the outside of the old sheaths and growth of new 

 filaments therefrom compound masses of appreciable 



s 



Fig. 56. Trichobacteria. 



a, b, c, Leptothrix {Streptothrix, or Chlamydothrix) . a, a colony; b, a single filament; c, spore 

 formation; d, e, f, Crenothrix; d, a single growing filament; e, a fruiting filament; /, a 

 compound colony; g, Cladothrix, a branching filament; h, Beggiatoa, younger and older 

 filaments, the latter showing sulphur granules, and no septa between cells of the filament. 



size are produced. In the sheaths of the filaments a 

 hydroxide of iron is deposited (for Crenothrix possesses 

 the power of oxidizing certain forms of iron) ; and with 

 continued growth the deposits sometimes become 

 sufficient to make trouble in city water supply systems 

 by stoppage of the pipes. In nature, also, certain 

 deposits of iron are due to this and allied forms properly 

 known as iron bacteria. Cladothrix (Fig. 56 g), is a 

 related form that exhibits a peculiar type of branching 

 in its slender cylindric filaments. 



