998 MANUAL OF DETERMINATIVE BACTERIOLOGY 



middle. Movements, if any, are of a slow, rolling, jerky type and are dependent 

 upon the presence of a substrate. No special organs of locomotion are known. In 

 their natural habitat, the cells contain sulfur droplets and sometimes additional in- 

 clusions, such as large spherules of calcium carbonate. 



The type species is Achromatium oxalijennn Schewiakoff. 



It is not easy as yet to determine whether several species should be recognized in 

 this genus. There appears to be some justification for differentiating between the 

 forms which contain the characteristic and conspicuous calcium carbonate inclusions 

 and forms in which these large spherules are lacking. The former have been re- 

 ported mostly from fresh or brackish water environments, while the characteristic 

 habitat of the latter seems to be marine. It is, of course, probable that the internal 

 deposition of calcium carbonate depends upon the composition of the environment, 

 so that the distinction may prove arbitrary and non-specific. 



Achromatium cells of widely different sizes have been described. Schewiakoff 

 (tjb. einen neuen bacterienahnlichen Organismus des Siisswassers, Habilitations- 

 schrift, Heidelberg, 1893) mentions a variation of 15 to 43 microns in length, and 9 to 

 22 microns in width for Achromatium oxalijeriim. Larger cells have been observed 

 by Warming (Videnskab. Meddel. naturhistor. Foren., Kjobenhavn, 1875, Xo. 20-28, 

 360; size to 85 microns), andTsy Virieux (Ann. Sci. Xatur., S^r. 9, 18, 1913, 265; size 

 to 95 microns in length). 



Nadson (Bull. Jard. Imp. Botan., St. P^tersb., 13, 1913, 106; Jour. Microb., St. 

 P^tersb., 1, 1914, 52) proposed the name Achromatium gigas for the larger organisms; 

 also West and Griffiths (Ann. Bot., £7, 1913, 83) created two species, Hillhousia 

 mirabilis, with sizes of 42 to 86 microns long by 20 to 33 microns wide, and Hillhousia 

 pahistris, measuring on the average 14 by 25 microns, for the same group of svdfur 

 bacteria. 



However, Bersa (Sitzungsber. Akad. Wiss., Wien, Mathem.-naturw. Kl., I, 129, 

 1920, 233) observed so many intermediate sizes that he recognized only a single 

 species. A'adson and Wislouch (Bull. Princ. Jard. Botan., Picpubl. Kusse, 22, 1923, 

 Suppl. 1, 33) arrived at the same conclusion, and this view is accepted here. 



The marine Achromatium types which do not contain calcium carbonate crystals, 

 also have been segregated into species on the basis of their size. Here again, there 

 does not seem to be any valid reason for maintaining several species as there is a 

 continuous series of intermediate forms. 



Thus, the organisms previously described as Achromatium oxaliferum, Achroma- 

 tium gigas, Hillhousia mirahilis and Hillhousia palustris are provisionally treated 

 here as one species, while the marine counterpart, Thiophysa volutans, is combined 

 with Thiophysa macrophysa and Tlnospliacrclla amylifera, all three being regarded 

 as Achromatium rolutaiis. 



Key to the species of genus Achromatitim. 



I. Organisms characteristically containing calcium carbonate crystals in the form 

 of highly retractile, large spherules. Occur mostly in fresh water and brackish 

 muds. 



1. Achromatium uxalijerum. 



II. Organisms naturally occurring without such calcium carbonate inclusions. 

 Found in marine mud. 



2. Achrnmntiint) volutans. 



