FAMILY I. THIORHODACEAE 



49 



B. Cells less than 3 microns in width. 



2. Rhabdomonas gracilis. 



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



3. Rhabdomonas linsbaueri. 



1. Rhabdomonas rosea Cohn, 1875. 

 (Cohn, Beitr. Biol. Pfl., 1, Heft 3, 1875, 167; 

 Beggiatoa roseo-persicina Zopf, Z. Morphol. 

 d. Spaltpfianzen, Leipzig, 1882, 30; Rhabdo- 

 chromatium roseiim Winogradsky, Schwefel- 

 bacterien, Leipzig, 1888, 100; Rhabdochro- 

 matium fusiforyne Winogradsky , ibid., 102.) 



ro'se.a. L. adj. roseus rosy, rose-red. 



Cells uneven in width and length, often 

 swollen to spindle-shaped, sometimes tend- 

 ing towards filamentous growth. The great- 

 est width of a spindle-shaped or fusiform 

 cell may be close to 10 microns; in the more 

 filamentous structures it is usually around 

 5 microns. The length varies between 10 and 

 30 microns for single cells; filamentous 

 forms, frequently showing bulges and con- 

 strictions suggestive of compound struc- 

 tures in which cell division has been incom- 

 plete, may attain considerably greater 

 lengths, up to 100 microns. The ends of 

 spindle-shaped cells often taper to very fine 

 points or attenuated fibers; also, filaments 

 are generally thinner toward the extrem- 

 ities. Single individuals and short filaments 

 are motile by means of polar flagella, long 

 filaments rarely motile. The ends of a fila- 

 ment may become pinched off and swim 

 away. 



Color rose-red; cells are usually filled with 

 sulfur globules. 



There is no good reason for maintaining 

 Rhabdomonas fusiformis (Rhabdochromatium 

 fusiforme Winogradsky) as a separate 

 species; the variations in size and shape 

 bring this form well within the range of 

 Rhabdomonas rosea. Present indications 

 strongly suggest that the latter species 

 should be regarded as a peculiar develop- 

 mental form of Chromatium okenii. 



Habitat: Mud and stagnant water con- 

 taining hydrogen sulfide and exposed to 

 light; sulfur springs. 



Illustrations: Cohn, op. cit., 1875, PI. VI, 

 fig. 14; Warming, Vidensk. Meddel. natur- 

 histor. Foren., Kjobenhavn, 1876, PI. VII, 

 fig. Ic-e; Zopf, op. cit., 1882, PI. V, fig. 2b; 



Winogradsky, op. cit., 1888, PI. IV, fig. 9-11, 

 13-14. 



2. Rhabdomonas gracilis (Warming, 

 1876) Bergey et al., 1923. {Monas gracilis 

 Warming, Vidensk. Meddel. naturhist. 

 Foren., Kjobenhavn, 1876, 331; Rhabdochro- 

 matium minus Winogradsky, Schwefelbac- 

 terien, Leipzig, 1888, 102; Rhodocapsa sus- 

 pensa Molisch, Die Purpurbakterien, Jena, 

 1907, 17; Bergey et al.. Manual, 1st ed., 

 1923, 402.) 



gra'ci.lis. L. adj. gracilis thin, slender. 



Cells much smaller than those of Rhabdo- 

 monas rosea and with less tendency to form 

 fusiform cells. Usually filamentous, more or 

 less cylindrical, often with constrictions, 

 but found up to 60 microns in length. 

 Shorter filaments motile. Polar flagellate. 

 Slime formation may occur under special 

 conditions. Rose-red. Sulfur globules. 

 Probably an abnormal growth form of Chro- 

 matium virosum. 



Habitat: Mud and stagnant water con- 

 taining hydrogen sulfide and exposed to 

 light; sulfur springs. 



Illustrations: Warming, op. cit., 1876, PI. 

 VII, fig. 5; Winogradsky, op. cit., 1888, PI. 

 IV, fig. 12; Molisch, op. cit., 1907, PI. II, fig. 

 11-12. 



3. Rhabdomonas linsbaueri (Gickl- 

 horn, 1921) van Niel, 1948. (Rhabdochroma- 

 tium linsbaueri Gicklhorn, Ber. d. deut. bot. 

 Ges., 39, 1921, 312; van Niel, in Manual, 6th 

 ed., 1948, 855.) 



lins.bau'er.i. M.L. gen. noun linsbaueri of 

 Linsbauer; named for K. Linsbauer, an 

 Austrian botanist. 



Cells resemble those of Rhabdomonas rosea, 

 irregular, rod-shaped, 3 to 5 microns wide, 

 up to 30 microns in length. 



The characteristic feature of the species, 

 and the chief means of differentiation, is the 

 occurrence of calcium carbonate inclusions 

 in addition to the sulfur globules in the cells. 

 Whether this is strictly an environmentally 

 conditioned characteristic, due to the 

 photosynthetic development of the bacteria 



