112 TAXONOMY 



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. This genus moves 

 by means of an undulating 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 classifica- 

 tion, Artificial). 



The cells contain bacteriopurpurin and on this account may 

 be red, rose, or violet. Sulphur granules may also be in- 

 cluded within the cells. 



I Subfamily: Thiocapsaceae. 



The cells are united into colonies. Cell division takes place 

 in three directions of space. 



Genus : Thiocystis Winogradsky. 



The colonies are small, compact, and enveloped either 

 singly or in groups by a gelatinous cyst. The colonies are 

 also capable of breaking up and the cells moving about. 



Genus : Thiocapsa Winogradsky. 



The cells are globular in shape and spread out on a sub- 

 stratum in flat colonies. These colonies are surrounded by a 



