RHODO'THIOBACTERIA 139 



in shape, ranging from a very much elongated form to one 

 that is completely spherical. Multiplication is by simple 

 fission, the cell usually dividing at the middle. In one species 

 a process has been observed which may be sexual. 



Chromatium Okenii (Ehrenberg), Perty. 



Literature, — As for genus. 



Description. — It is somewhat doubtful whether all the forms 

 described under the name of Chromatiimi Okeniihy different in- 

 vestigators are the same species. It is typically a free, wine- 

 red, coloured, motile organism, of an elliptical-cylindrical shape. 

 Motility appears to be due to the lashing of a single large wavy 

 cilium, which is readily made visible by staining with carbol- 

 fuchsin (Fig. 2'jh). However, it has been shown by Kolkwitz 

 that the apparently single cilium is compound and that it may 

 be composed of as many as forty cilia. He found that when 

 the slime which covers the cilia was removed, the individual 

 cilia came apart. When completely separated from the slime 

 they appear as very fine, wavy, filaments, that are on the 

 margin of visibility. Even in healthy cultures, some forms 

 may be observed which are strikingly different from the normal 

 shape. Thus bean-shaped or club-shaped individuals are not 

 uncommon in such cultures ; and there is often a noticeable 

 variation in their size. Scarcely two observers agree on the 

 range of its dimensions. The average is 



7-5— iS^a X 5-0— 6-3/x. 



Another range that has been given is 



16/i, X 6-0 — 6-3/i. 



Buder (i) has given lOyi as an extreme length for normal 

 specimens. Warming has shown that Chromatium Okenii 

 may exhibit a large range of pleomorphic forms ; and Zopf (i) 

 has come to the conclusion that so many intermediates may 

 be found between Chr. Okenii and Beggiatoa roseo-persicina 

 that these two apparently widely different organisms may be 

 regarded as the same species. The point cannot be settled 

 without further research. 



