FAMILY BEGGIATOACEAE 991 



tached. Exi.'ilence of a sheath not dehaitely established. Movements of the fila- 

 ments dependent upon a solid substratum over which they slide in the same manner 

 as species of Oscillatoria. Sliding movements often accompanied by rotation of 

 filaments around long axis. Reproduction by transverse fission of segments; the 

 filaments may also break up into smaller units, each continuing a separate existence. 

 The latter mode of multiplication corresponds to that by means of the .so-called 

 motile conidia or segments in Thiothrix. 



The type species is Beggiatoa alba (Vaucher) Trevisan. 



In this genus, also, the species so far described are differentiated on the basis of 

 dimensions. The range of sizes for separate species appears, in most cases, quite 

 arbitrary, especially in view of the existence of practically all intermediate stages. 

 Since the smaller forms have been found both in fresh water and marine environments 

 (Bavendamm, Die farblosen u. roten Schwefelbakterien, Pflanzenforschung, Heft 2, 

 192-4, 104), the previously described Beggiatoa marina has been omitted as a separate 

 species. Pure culture studies may establish more staistactory methods of differen- 

 tiation and a better understanding of speciation. 



Key to the species of genus Beggiatoa. 



I. Diameter of filaments greater than 25 microns. 



1. Beggiatoa gigantea. 

 II. Diameter of filaments less than 25 microns. 



A. Diameter of filaments greater than 15 microns. 



2. Beggiatoa mirabilis. 



B. Diameter of filaments less than 15 microns. 



1. Diameter of filaments greater than 5 microns. 



3. Beggiatoa arachnoidea. 



2. Diameter of filaments less than 5 microns. 



a. Diameter of filaments greater than 2.5 microns. 



4. Beggiatoa alba. 



aa. Diameter of filaments less than 2.5 microns. 



b. Diameter of filaments gi-eater than 1 micron. 



5. Beggiatoa leptomitiformis. 

 bb. Diameter of filaments less than 1 micron. 



6. Beggiatoa minima. 



1. Beggiatoa gigantea Klas. (Arch. f. ments clearly segmented; length of -seg- 



Alikrobiol., 8, 1937, 318; includes the ments 5 to 13, average 8.5 microns, 



arge forms of Beggiatoa mirabilis Cohn, Terminal cells rounded or tapering. 



Hedwigia, 4, 1865, 81.) From Greek when the filaments are in healthy 



f/'J/as, giant. condition thev are of uniform width; 



Filaments 26.4 to 55, average 35 to 40 ^^^,1^:,^^ ^f the sides indicates unfavor- 



microns in diameter. Klas, in his diag- ,, ,.,. 



. ' ^ able conditions, 



nosis, gives 26.4 to 42.9 microns as dimen- tt i -x . » ^^ . ■ ^ ■, ^ 



™, . ,, , , ,, , Habitat: Apparently restricted to ma- 



sions. ihis would exclude the largest . . . . , , 



J. CD ■ , ■ I.T J -u 1 nne environments containing hydrogen 



forms of Beggiatoa mirabilis described a j » 



by Hinze (Ber. d. deut. bot. Ges., 19, ""l^de. Frequent on decaymg marine 



1901 , 369) . Since the proposal of a sepa- ^^^^^ ■ 

 rate species for such organisms appears 



at present unjustified, the maximum 2. Beggiatoa mirabilis Cohn emend. 



diameter has here been increased. Fila- Klas. (Cohn, Hedwigia, 4, 1865, 81; 



