io6 



SULPHUR BACTERIA 



hardens and becomes detached from the remainder of the 

 organism, forming a covering which encloses the Hving part of 

 the cell. Finally, although short lengths of Beggiatoa do not 

 show any diflerence in thickness at different parts of the thread, 

 longer filaments show differences which may be pronounced. 

 In Thiothrix the presence of a fixed hardened slime sheath 

 has some influence in determining the thickness, since normally 

 the apex, where the slime is softer, is thicker than the base, 

 where the slime is firmer. 



'X 



M 



H 



a t> c 



Fig. g. — Thiothvix Rod-Gonidia X looo. 



a. — Young thread before active slime formation. 



b. — Slightly older thread, in which slime formation has commenced. Slime 



shown at x. 

 c. — Later stage. Slime has hardened into a sheath. 

 Rod-Gonidia (d) are in process of expiilsion from open apex of sheath. 



Description. — Colourless sulphur-containing threads, non- 

 motile in mature form, and surrounded by an enveloping 

 sheath of hardened slime. Usually attached by a slimy 

 anchoring organ to various objects in the water. Distinction 

 between base and apex much more marked than in Beggiatoa, 

 and the middle portion may occasionally be thicker than 



