FAMILY BEGGIATOACEAE 



989 



of the filaments and their habitat, the only criteria used by previous authors for the 

 differentiation of the seven published species. The validity of these distinguishing 

 characteristics is, however, doubtful because their constancy has not been sufficiently 

 established; so far the morphology of the Thiothrix species has not been studied in 

 pure cultures. 



Key to the species of fjeiius Thiothrix. 



I. Found in fresh water environments. 



A. Diameter of filaments about 2 (1.4 to 3.0) microns. 



1. Thiothrix nivea. 



B. Diameter of filaments about 1 micron. 



2. Thiothrix tenuis. 



C. Diameter of filaments less than 0.5 micron. 



3. Thiothrix tenuissinia. 

 II. Found in marine en\aronments. 



A. Diameter of filaments averages about 20 microns (actual range 15 to 30 mi- 



crons). 



■4. Thiothrix voukii. 



B. Diameter of filaments about 4 (4.4 to 6.6) microns. Segments about 25 microns 



long. 



5. Thiothrix longiarticulata. 



C. Diameter of filaments about 3 (1.8 to 5) microns. Segments about 1 micron 



long. 



6. T'Inothrix annulata. 



D. Diameter of filaments about 1 (0.8 to 1.3) micron. 



7. Tlnothnx marina. 



1. Thiothrix nivea (Rabenhorst) Wino- 

 gradsky. {Beggiaioa nivea Rabenhorst, 

 Flora europaea algarum, 2, 1865, 94; 

 Leptotrichia nivea De Toni and Trevisan, 

 in Saccardo, Sylloge Fungorum, 8, 1889, 

 934; Sympliyothrix nivea Wartman and 

 Schenk, Schweiz. Kryptogamenflora; 

 Winogradsky, Beitr. z. Morph. u. Phy- 

 siol, d. Bact., I, Schwefelbacterien, 

 1888, 39.) From Latin jiiveus, snowy. 



Filaments with a thin sheath, diameter 

 2.0 to 3.0 microns at base, 1.7 microns 

 in the middle, 1.4 to 1.5 microns at tip. 

 As long as the filaments contain sulfur 

 globules, segmentation is invisible; 

 length of segments 4 to 15 microns, the 

 longer ones usually near apex, the shorter 

 ones near base. 



Motile segments (so-called conidia) 

 mostly single, 8 to 15 microns long, some- 

 times in short filaments of 2 to 4 cells 

 and up to 40 microns long. These seg- 

 ments may settle and develop near the 



base of the mother filament or on a fila- 

 ment itself, forming verticillate struc- 

 tures. These have been described as 

 Thiothrix nivea var. verticillata Miyoshi 

 (Jour. Coll. Sci., Imp. Univ. Tokyo, 10, 

 1897, 156). 



Habitat: Fresh water environments 

 where hydrogen sulfide is present (sulfur 

 springs, stagnant pools, on submerged 

 decaying vegetation, etc.). 



2. Thiothrix tenuis Winogradsky. 

 (Beggiatoa alba var. uniserialis Engler, 

 tjb. die Pilz -Vegetation des weissen oder 

 todten Grundes in der Kieler Bucht, 1883, 

 4; Winogradsky, Beitr. z. Morph. u. 

 Physiol, d. Bact., I, Schwefelbacterien, 

 1888, 40.) From Latin tenuis, slender. 



Filaments about 1.0 micron in diam- 

 eter, of nearly uniform thickness. Often 

 in dense, felted masses. Segments 4 to 

 5 microns long. 



Habitat: Fresh water environments 



