THE GENERA CRENOTHRIX AND CLADOTHRIX. 359 



false branching may also develop. Hence there ensues a forma- 

 tion the internal structure of which is represented diagrammatically 

 in Fig. 68. In many species (not depicted here) the sheath be- 

 comes greatly thickened at the base, where it attains a diameter 

 many times exceeding that of the cells it encloses, but tapers off 

 gradually towards the free extremity. Cladothrix dichotoma also 

 differs from the above-mentioned thread bacteria in another impor- 

 tant particular, viz., by the production of rod-shaped roving cells, 

 called rod-gonidia, which develop at the extremity of the threads, 

 and, after being initially embedded in the 

 swollen sheath (Fig. 69), are liberated, 

 wander about, and finally settle down to 

 form new threads by subdivision and 

 sheath-formation. 



Allied to Cladothrix dichotoma 

 though not, as ZOPF (VII.) opined, be- 

 longing to the morphological cycle of this 

 organism is Leptothrix ochracea, which 

 was first described by Kiitzing. A second 

 sheath-forming thread bacterium, allied to 

 the genus Cladothrix, was also examined 

 by him, and named Sphcerotilus natans. 

 It is still too imperfectly known to be 

 dilated upon here, although ED. EIDAM (II.) 

 also occupied himself with it. Associated 

 with this colourless species is a second 

 (coloured) species, discovered by W. 

 ZOPF (VIII.) in a Silesian river receiving 

 the drainage from a sugar-works. The 

 cells of this, Sphcerotilus roseus, contain a 

 yellow and a red colouring matter, which circumstance is of itself 

 sufficient to distinguish it from all other (colourless) species of 

 thread bacteria hitherto mentioned. 



The genus Phragmidiothrix, one species of which Ph. multi- 

 septata 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. 



FIG. 69. 

 Cladothrix dichotoma. 



Subdivision into roving rods 

 at the extremity of a 

 thread, s. the loosened 

 sheath ; g. the roving 

 rods with their (lateral) 

 cilia (c). Magn. 1000. 

 (After A. Fischer.) Cilia 

 staining. 



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 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 



