PHYSIOLOGY OF TIIK IKON HACTKKIA 275 



The genus Pkragniidioth/riX) one species of which 7V*. mtdtiaeptata, was 

 discovered by ENGLER (I.) in the so-called "dead ground " of the Bay of Kiel, 

 differs from all the foregoing in the absence of sheath formation. 



198. Physiology of the Iron Bacteria. 



It is not always possible to discern the structure of these thread bacteria 

 without some preliminary treatment, because in most cases the sheaths are 



^ \ 









\ 





FIG. 67. Cladothrix dichotoma. 



Portion of a thread with several branching forks. 

 Stained with fuchsine solution, and thus reveal- 

 ing the articulation into long rods. Magn. 

 540. (After Zopf.) 



FIG. 68. 



Diagram of the false branching of 

 Cladothrix. 



surrounded and permeated by red-brown masses of ferric oxide. These deposits 

 and accumulations are characteristic of these plants, and facilitate their detection 

 and discovery. Since other fungi exposed to the same conditions do not 

 exhibit this peculiarity, Cohn formed the opinion that its occurrence is intimately 

 connected with the vital activity of the thread bacteria, the ferric oxide being 

 deposited in their sheathing in the same way that silica is accumulated in the 

 plates of the diatoms We are indebted to 8. WINOGRADSKY (IV.) for proving 

 the correctness of this view, and for refuting the opinion of Zopf that the deposi- 

 tion is purely mechanical ; and we have to thank the same observer for the more 

 intimate investigation of the process in question. 



The species Crenothrix polyspora, Cladothrix dickotcma, Leptothrix ochracea t &c. t 



