6o 



MORPHOLOGY AND CULTURE OF MICROORGANISMS. 



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: Sphserotilus KTJTZING, 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. 40) . 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 sulphur. 

 The cells are colorless or pigmented rose, violet, or red by 

 bacteriopurpurin. The cells are never pigmented green. 

 I. Family : Beggiatoaceae TREVISAN. 

 Filamentous bacteria which do not contain bacteriopur- 

 purin. The cells contain sulphur granules. Reproduction 

 takes place in one direction of space. 

 Genus : Thiothrix WINOGRADSKY. 

 The cells are non-motile 

 and the threads are attached to 

 some object. The threads are 

 surrounded by a delicate sheath 



and the cells contain sulphur granules. Gonidia are pro- 

 duced at the end of the threads. These gonidia ear 

 motile and finally attach themselves to some object, and, 

 according to some authors, bend at right angles in the 

 middle and grow into new threads. 

 Genus : Beggiatoa TREVISAN. 

 The threads are not surrounded by a sheath and 

 are formed of flat cells. The cells are not attached 

 (Fig. 41). This genus moves by means of an undula- 

 ting membrane similar to Oscillaria. As the organism 

 moves, it rotates on its long axis and swings its free 

 ends. Gonidia are unknown and reproduction takes 

 place by a division and separation of the threads. 



II. Family: Rhodobacteriaceae (WINOGRADSKY'S 

 classification, artificial). 



The cells contain bacteriopurpurin and on this account may be red, rose, or violet. 

 Sulphur granules may also be included within the cells. 



FIG. 40. C lado- 

 thrix dichotoma Cohn. 

 (After Fischer from 

 Schmidt and Weiss.} 



FIG. 41. Beggiatoa alba. 

 Vaucher, Trevisan. (After 

 Winogradsky from Schmidt 

 and Weiss.) 



