CLADOTHKIX 513 



LEPTOTHEIX OCHRACEA (Kiitzing) 



Authority. — Winogradsky, 'Ueber Eisenbakterien,' Botanische Zeitung, 

 No. 17, 1888, p. 262. 



"Where Found. — Very frequently found in waters containing iron. Wino- 

 gradsky states that the more ferrous oxide there is present in the water the 

 larger is the number of ' iron-bacteria ' found, and that the latter grow luxuri- 

 antly in waters or liquids containing very small quantities of organic matter. 

 In vessels containing some of this water small rust-coloured flakes appear on 

 the surface of the liquid, whilst rust-coloured patches appear on the sides of the 

 vessel as well, the latter becoming covered, in from 8 to 10 days, with thick 

 yellowish brown growths. Large zoogloea masses, similar in colour, are pro- 

 duced on the surface and gradually sink to the bottom. 



Microscopic Appearance. — The threads consist of very thin rods, which are 

 enclosed in a more or less thick sheath, within which they occur singly or in 

 groups. A young thread will adhere firmly to the glass with one end, the other 

 being quite free in the liquid. At the base the sheath is many times thicker 

 than the rodlet, whilst it gradually tapers towards the free extremity, the last 

 2 to 10 rodlets usually being without any sheath. As soon as the sheath becomes 

 thick and brown, the rods either quite abandon it, or are found in the act of 

 creeping out of it. In this manner comparatively large knotty and branched * 

 structures are produced, consisting almost entirely of empty ochre-coloured 

 sheaths, whilst the living threads which have generated this structure are 

 themselves found attached to the sheath as short thin colourless little terminal 

 branches. Multiplication takes place by detachment of actively motile rodlets, 

 which after a time sink to the bottom and grow out into threads, formation of 

 the brown sheath at once also commencing. Winogi'adsky found that the 

 sheath only became brown in colour in waters containing ferrous oxide, and that 

 this was effected through the oxidation of the ferrous oxide taking place in the 

 substance of the thread itself. In the absence of ferrous oxide the threads will 

 not grow. 



* The branching is brought about by the thread breaking into two, and from one or 

 both of the ends thus produced a new thread grows out. The place where the division 

 took place is rendered imperceptible by the gelatinous excretion of the growing 

 threads, so that ultimately the latter appear like thin branches on a thick brown 

 thread, the latter being, however, generally only an empty sheath. 



CLADOTHEIX (Cohn) 



According to Mac6 {TraiU pratique de BacUriologie, 2nd edit., 1892, p. 662, 

 the genus Cladothrix is distinguished from the genus Leptothrix by the 

 presence of real branchings and the entire absence of a gelatinous sheath. 



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