FAMILY ACHROMATIACEAE 997 



FAMILY A. ACHROMATIACEAE MASSART. 



(Rec. Inst. Bot. Univ. Bruxelles, 5, 1902, 251.) 



Cells large, spherical to ovoid in shape, sometimes rod-shaped, may contain 

 globules of sulfur and/or calcium carbonate crystals. Do not possess photosynthetic 

 pigments. Fresh water and marine forms. 



A satisfactory differentiation of the genera Achromatium , Thiophysa, and Thio- 

 sphaerella is at present well-nigh impossible. They have here been combined into a 

 single genus, Achromatium. 



Achromatium mobile Lauterborn (Verhandl. Natur-histor.-Mediz. Vereins Heidel- 

 berg, N.F., 13, 1915, 413) is fundamentally different from the other members of the 

 genus. It possesses a clearly visible polar flagellum, suggesting its close affinity 

 with the Pseudomonadaceae among the Eubacteriales. Whether it is a true sulfur 

 bacterium has not been established with certainty; this appears very doubtful in 

 the case of the two similar forms described as Pseudomonas hipunctata and Pseudo- 

 monas hyalina by Gicklhorn (Cent. f. Bakt., II Abt., 50, 1920, 425, 426). Utermohl 

 and Koppe (Verhandl. Intern. Ver. f. theoret. u. angew. Limnologie, 1913, 86 and 

 Archiv f. Hydrobiol., Suppl. Bd. 5, 1925, 234) have pi-oposed the generic name Macro- 

 monas for this group. This has been adopted here. 



All of the above mentioned organisms have so far been studied exclusively as 

 found in their natural habitats. Pure culture studies are greatly needed. These 

 may show that the peculiar calcium carbonate inclusions (not calcium oxalate as 

 thought by Schew^iakoff , nor calcium thiosulfate as believed by Hannevart) in Achro- 

 matium oxaliferum and in Macromonas hipunctata occur only under special environ- 

 mental conditions. 



Key to the genera of family Achromatiaceae. 



I. Large, ovoid to spherical organisms, normally containing sulfur globules when 

 found in the presence of hydrogen sulfide. 



A. Non-motile, or slowly, jerkilj^ sliding across the substrate. 



Genus I. Achromatium, p. 997. 



B. Actively motile, independent of the substrate. 



Genus II. Tliiovulum, p. 999. 

 II. Rod -shaped and curved organisms, motile by means of polar flagella. 



A. Bean-shaped to short rod-shaped organisms which may contain small sulfur 

 globules, but are chieffy characterized by large, round spherules of calcium 

 carbonate as cell inclusions. The polar flagellum is often visible in the 

 larger forms without special staining. 



Genus III. Macromonas, p. 1000. 



Genus I. Achromatium Schewiakoff . 



(Schewiakoff, tjb. einen neuon bacterienahnlichen Organismus des Siisswassers, 

 Ilabilitationsschr., Heidelberg, 1893; Modderula Frenzel, Biol. Centralbl., 17, 1897, 

 801; Hillhousia West and Griffiths, Proc. Roy. Soc, B, 81, 1909, 389). From Greek 

 a, without and chroma, color. 



Thiophysa Hinze (Ber. d. deut. bot. Ges., 21, 1903, 309j and Thiosphaerella Nadson 

 (Jour. Microbiol., St. Petersb., /, 1914, 72) are also included in the genus as defined 

 here. 



Unicellular organisms with large cells, shortly cylindrical with hemispherical 

 extremities, also ellipsoidal to spherical. Cells divide by a constriction in the 



