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MANUAL OF DETERMINATIVE BACTERIOLOGY 



damm (Die farbloseii unci roten Schwefelbakterieii, Ffianzenforschuiig, Hel't 2, 1924, 

 129) favor generic rank. 



The type species is Rhabdomonas roseus Cohn. 



Key to the species of genus Rhabdomonas. 



I. Cells not containing calcium carbonate inclusions in addition to sulfur globules, 

 a. Cells more than 3 microns in width. 



1. Rhabdomonas i-osea. 

 aa. Cells less than 3 microns in width. 



2. Rhabdomonas (jracilis. 



II. Cells containing calcium carbonate inclusions in addition to sulfur globules. 



3. Rhabdomo7ias linshaueri. 



1. Rhabdomonas rosea Cohn. (Cohn, 

 Beitr. Biol. Pfi., 1, Heft 3, 1875, 167; 

 Beggialoa roseo-persicina Zopf, Z. Mor- 

 phol. il. Spaltpflanzen, Leipzig, 1882, 30; 

 Rhubdochroniatiani roseum Winogradsky, 

 Schwefelbacterien, Leipzig, 1888, 100; 

 Rhabdochrnniati uni fusiforrne Winograd- 

 sky, ibid., 102; Pseudomonas rosea Mi- 

 gula, in Engler and Prantl, Die natiir- 

 lichen Pflanzenfam., 1, la, 1895, 30.) 

 From Latin roseus, rose-colorod. 



Cells: Uneven in width and length, 

 often swollen to spindle-shaped, some- 

 times tending towards filamentous 

 growth. The greatest width of a 

 spindle-shaped or fusiform cell may be 

 close to 10 microns; in the more fila- 

 mentous structures it is usually around 

 5 microns. The length varies between 

 10 and .30 microns for single cells; fila- 

 mentous forms, frequently showing 

 bulges and constrictions suggestive of 

 compound structures in which cell divi- 

 sion has lieen incomplete, may attain 

 considerably greater lengths, up to 100 

 microns. The ends of spindle-shaped 

 cells often taper to verj^ fine points or 

 attenuated fibers; also filaments are 

 generally thinner toward the extremities. 

 Single individuals and short filaments 

 are motile by means of polar flagella, 

 long filaments rarely motile. The ends 

 of a filament may become pinched off 

 and swim away. 



Color rose-red; cells are usually filled 

 with sulfur globules. 



There is no good reason for maintain- 



ing Rhabdomonas fusiformis (Rhabdo- 

 chromaiium fusiforrne Winogradsky) as a 

 separate species; the variations in size 

 and shape bring this form well within 

 the range of Rhabdomonas rosea. Pres- 

 ent indications strongly suggest that 

 the latter species should be regarded as 

 a peculiar developmental form of Chro- 

 matium okenii. 



Habitat: Mud and stagnant water con- 

 taining hydrogen sulfide and exposed to 

 light; sulfur springs. 



Illustrations: Cohn, loc. cit., PI. VI, 

 fig. 14; Warming, Vidensk. Meddel. 

 naturhistor. Forcn., Kjobenhavn, 1876, 

 PI. VII, fig. Ic-e; Zopf, loc. cit., PI. V, 

 fig. 2b; Winogradsky, loc. cit., PI. IV, 

 fig. 9-11, 13-14. 



2. Rhabdomonas gracilis (Warming) 

 Migula. [Monas gracilis Warming, 

 Vidensk. Meddel. naturhist. Foren., 

 Kjobenhavn, 1876, 331; Rhabdochro- 

 matium minus Winogradsky, Schwefel- 

 liacterien, Leipzig, 1888, 102; Rhabdo- 

 chromatium gracile Migula, Syst. d. 

 Bakt., 2, 1900, 1049; Rhodocapsa sus- 

 pensa Molisch, Die Purpurbakterien, 

 Jena, 1907, 17; Rhabdomonas minor 

 Bergey et al.. Manual, 3rd ed., 1930, 

 532.) From Latin gracilis, slender. 



Cells: Much smaller than those of 

 Rhabdomonas rosea, and with less tend- 

 ency to form fusiform cells. Usually 

 filamentous, more or less cylindrical, 

 often with constrictions, but found up 



