502 GENERAL SYSTEMATIC BACTERIOLOGY 



no bacteriopurpurin, and with cells not in thread-like filaments. The 

 following genera are included: Sulfomonas, Thiomonas, Thiococcus 

 and Thiospirillum. There is no genus Thiobacter or Thiobacterium 

 hence the family name is incorrectly constituted. 



Thiobacteriales. An order of bacteria named by Buchanan (1917) 

 to include the sulphur bacteria. The following is his description 

 (1918, p. 461). 



Cells various, typically containiBg either granules of free sulphur, or bacterio- 

 purpurin, or both, usually growing best in the presence of hydrogen sulphide. 

 The cells are plant-like, not protozoan-like, not producing a pseudoplasmodium 

 or a highly developed encysted resting stage. Spores are rarely or never formed. 



Classification within this group is in a very unsatisfactory and very superficial 

 state. Few investigators have studied these forms, and most of the work is old, 

 and in need of careful revision. Undoubtedly many of the genera are to be 

 regarded as growth forms, merely. 



Three families were recognized; Achromatiaceae, Beggiatoaceae and 

 Rhodobacteriaceae. The order was recognized by Winslow et al. (Com- 

 mittee Soc. Am. Bact., 1917, p. 549, and 1920, p. 196) by Castellani 

 and Chalmers (1919, p. 924), Heller (1921, p. 449) and Bergey et al 

 (1923, p. 393). 



Thiocapsa. A genus of sulphur bacteria described by Winogradsky 

 (1888, p. 84) with the species Thiocapsa roseo-persicina. The genus 

 resembles in the grouping and multiplication of the cells the algal genus 

 Aphanocapsa. Cell division occurs in all directions of space, the cells 

 are spherical, with thick confluent membranes, which unite to form a 

 structureless gelatinous layer. The cells are a bright rose red color 

 and contain numerous sulphur granules, 



Trevisan (1889, p. 28) includes Thiocapsa as the fourth genus of the 

 tribe Sarcinee. The description reads "Cocchi lassamente aggregati 

 in famiglie irregolari nella ganga mucosa disugualmente spianata senza 

 forma definita. Temnogenesi in tre direzioni." 



De Toni and Trevisan (1889, p. 1049) recognize this genus, as do 

 Migula (1900, p. 1043) (1904, p. 146), E. F. Smith (1905, p. 163) and 

 Frost (1911, p. 61). Smith gives the following description: 



Non-swarming, globose cells spread out upon the substratum in flat families, 

 which are loosely enveloped in a common gelatin. The membrane is split by the 

 growth of the family, and the cells are separated as if by the swelling of an inter- 

 mediate substance. 



Orla-Jensen (1909, p. 334) incorrectly made this a synon5an of 



Rhodocapsa. 



