RHODO-THIOBACTERIA 143 



Variant forms of Chromatiitm Okenii. — The tendency of 

 this species to vary both in size and in shape has been sufficiently 

 emphasized. The following organisms are, in the author's 

 opinion, merely variants of the highly pleomorphic Chromatium 

 Okenii. 



(a) Chromatium Okenii forma Weissii. 



Syn. Chromatium Weissii (Perty). 



Literature. — Perty, 1852 ; Winogradsky (2), 1888 ; Miyoshi, 

 1897; Strzeszewski (2), 1913; Lauterborn (7), 1915 ; 

 Bavendamm, 1924. 



Elongated form about ii-5ju. long and about 4-2/x thick. 

 Connected by transitional forms with the normal type of 

 Chromatium Okenii. 



o o 

 O 



o o 



Fig. 28. — Chromatium Weissii, Chromatium minus, Chvomatium viriosum, 

 Chromatium minutissimum (arranged in order from left to right) . 



[b] Chromatium Okenii forma minus. 

 Syn. Chromatium minus (Winogradsky). 



Literature. — Winogradsky (2), 1888 ; Migula (3), 1897 ; 



Strzeszewski (i), 1913 ; Bavendamm, 1924. 

 Described by Strzeszewski as an organism with numerous 

 intermediates bridging it to Chromatium Okenii forma Weissii. 



[c] Chromatium Okenii forma minutissimum 

 Syn. Chromatium minutissimum (Winogradsky). 

 Literature. — Winogradsky (2), 1888. 



Cells spherical or ellipsoidal, i — r2/x, in diameter. Indi- 

 vidual cells are colourless, but when seen in masses are of a 

 peach-fiower colour. 



Issatchenko (4) records that this organism can be made to 

 grow in a test-tube filled with mud and water, forming a rose- 

 coloured film on the surface, which is identical with a similar 



