112 



MOEPHOLOGY AND CULTUEE OF MICROORGANISMS 



Genus: Chlamydothrix Migtjla. 



The cells are cylindrical, non-motile, and arranged in unbranched threads and 

 surrounded by a sheath of varying thickness in diflferent species, being the same 

 diameter at apex and base (Fig. 86). Reproduction takes 

 place by means of gonidia, which are round and arise di- 

 rectly from the vegetative cell. This genus is called Lep- 

 tothrix by Ktjtzing and Streptothrix by Cohn. 

 Genus : Crenothrix Cohn. 



The cells are united together into filaments which are 

 unbranched. The filaments gradually enlarge toward the 

 free end, thus making a distinction between the apex and 

 base. The sheath which covers the filaments is thick and 

 often becomes infiltrated with the hydroxide of iron after 

 being cast off in water in which there is a large amount of 

 iron. Reproduction takes place by the formation of round 

 '■ gonidia which are formed in the beginning by division per- 

 pendicular to the long axis of ,the cell and later by division 

 in three directions of space. Only one or possibly two 

 species can be placed in this genus. 

 Genus : Phragmidiothrix Engler. 



The cells in the beginning form unbranched threads. 

 Cell division, takes place in three directions of space, thus 

 forming within the sheath a mass of cells. Later these cells 

 may burst through, multiply, and form branches after 

 acquiring sheaths. The sheath in this genus is quite thin 

 and can scarcely be seen. 



Genus : Sphaerotilus Kutzing, 

 1833 (Cladothrix Cohn). 



The cells are cylindrical and 

 the threads are surrounded by sheaths. Dichotomous 

 branching is present, and there is no differentiation in 

 size between the apex and base of the thread (Fig. 87). 

 Reproduction' takes place by means of gonidia which 

 swarm together within the cell. These gonidia burst 

 out of the cells, attach themselves to some object, and 

 grow into new threads. The gonidia are endowed with 

 flagella which are attached toward the end and below 

 the pole. 



II. Order: Thiobacteria (sulphur bacteria). 

 The cells do not possess any nucleus and contain sul- 

 phur. The cells are colorless or pigmented rose, violet, 

 or red by bacteriopurpurin. The cells are never pig- 

 mented green. 



I. Family : Beggiatoaceae Trevisan. 



Filamentous bacteria which do not contain bacteriopurpurin. The cell* contain 

 sulphur granules. Reproduction takes place in one direction of space. 



•Fig. Sj.-^Clado- 

 thrix dichotoma 

 Cohn. {After Fis- 

 cher from Schmidt 

 and Weiss.) 



Fig. 88. — Beggiatoa 

 alba. Vaucher, Trevi- 

 san. (After Winogradsky 

 from Schmidt and Weiss.) 



