82 SULPHUR BACTERIA 



therefore only a partial application. He divides the coloured 

 sulphur bacteria into six groups, the first four of which are 

 divided according to the number of directions in space in which 

 the cell divides, and the last two are separated from the rest by 

 being free instead of forming families. I'his classification, in 

 one respect, is not an advance on that of Winogradsky, for 

 in it also the number of dimensions in space in which an 

 organism divides is made the basis of the primary grouping. 



Molisch reduced Winogradsky's fourteen groups to six, as 

 he omitted the following : Thiocystis, Thiosarcina, Thiothece, 

 Thiodictyon, Thiopolycoccus, Rhabdochromatium, and Thio- 

 spirillmn. No reasons are given except that the classification 

 is made " auf Grund meiner Erfahrung." As Molisch's re- 

 searches did not deal, except incidentally, with the grouping 

 of the sulphur bacteria, his classification of these forms is 

 necessarily incomplete. He, however, added two genera to 

 the sulphur bacteria, namely Rhodocapsa and Rhodothece. 

 Both are sharply marked off from all the genera hitherto 

 included in the sulphur bacteria. In his own classification 

 they are included presumably in Rhodocapsaccce, although 

 he does not specify the genera of this sub-family in his 

 scheduled classification. 



A notable departure in the method of classification of 

 bacteria was made by Orla Jensen (1909). In the interval 

 the list of sulphur bacteria had been supplemented by the 

 discovery of the genus Thioploca by Lauterborn (1907). 

 Orla Jensen introduced entirely new factors in his classifica- 

 tion. Whilst using morphological characters for the main 

 groupings, the families and genera are separated on the basis 

 of physiological difterences. 



Orla Jensen's Classification. 



Two Orders are distinguished. 



I. Cephalotrichince. — Cells spherical, rod-shaped, or spiral. 

 Endospores formed only in a few sulphur-free spirilla. When 

 motile, mono- or lopho-trichous. Typically water bacteria. 

 Energy almost exclusively by oxidation processes. 



