SECTION E 



1. Multicellular organisms (sheathed or not sheathed) or chains of unicellular organisms 



enclosed in a sheath 2 



Note: This does not include chains of individually encapsulated cells or cells 

 in zoogloeal masses. 

 Not as above; proceed to Section F p. 1005 



2. Organisms enclosed in a common sheath 3 



Not as above 14 



3. Width of sheath increasing from the base to the tip; cells within the sheath divide 



transversely- and longitudinally towards the tip to produce large numbers of coccoid 



elements ; attached by means of a holdfast 4 



Not as above 5 



4. Cells within the basal portion of the sheath longer than wide; when growing in iron- or 



manganese-bearing waters, become heavily impregnated with iron or manganese 



Crenothrix p. 272 

 Cells within the basal portion of the sheath are wider than long; no iron deposited 



Phragmidiothrix p. 273 



5. Sheaths become impregnated with iron or manganese when growing in iron- or manga- 



nese-bearing waters or media 6 



Not as above 8 



6. Organisms in which the sheaths split longitudinally into fine, hair-like sections. The 



chain of cells remains attached to the hairs at several points and, with continued 

 growth, causes arching of the hairs and of the chain of cells within its new sheath, 



resulting in the formation of a helm-like mass Toxothrix p. 269 



Not as above 7 



7. Cells within the base of the sheath 2 by 10 microns, with rounded ends; divide trans- 



versely^ near the tip to produce spherical, non-motile cells which are extruded either 

 singly or in chains. The sheath is heavily impregnated with iron or manganese, be- 

 coming much wider at the base and tapering towards the tip; attached by a holdfast; 

 false branching is common Clonothrix p. 27 4 



In the absence of iron, cells within the sheath are of uniform size except during division. 

 During deposition of iron in the sheath, cells in the more heavily impregnated areas 

 become much narrower than normal; extruded cells are of the same dimensions as 



those within the sheath Leptothrix p. 26^. 



Note: Species of Sphaerotilus will also be found to terminate at this point if 

 grown in ferric ammonium citrate media. The genera are considered to be 

 identical by Pringsheim and others but this relationship has been disputed 

 by Beger (see Manual). 

 —8. Endospores produced within the cells of the trichome and located in an oblique position 



Coleoitiitus p. 8S6 



No endospores 9 



9. Organisms oxidize hydrogen sulfide, depositing sulfur inside the cells 10 



Organisms do not oxidize hydrogen sulfide and do not deposit sulfur internally. . . .11 



10. Several trichomes within a sheath Thioploca p. 841 



A single trichome in each sheath Thiothrix p. 842 



Note: The author has demonstrated that Sphaerotilus, when exposed to hydro- 

 gen sulfide, deposits sulfur internally. If Thiothrix forms uniseriate multicellu- 

 lar structures similar to those formed by Beggiatoa, as has been assumed in 

 this key, Sphaerotilus differs from it in the formation of single cells in chains. 



11. Single cells in chains within a common sheath; free cells motile by means of subpolar 



flagella or non-motile Sphaerotilus p. 263 



1003 



