12 CONSIDERATIONS INFLUENCING CLASSIFICATION 



Eubacteriales is defined to include not only the bacteria that are peritrichously 

 flagellated but also such non-motile forms as seem by their physiology to be 

 closely related to these peritrichous species. 



The placing of non-motile species of bacteria in systems of classification has 

 always caused difficulty. Some students think that lack of motility is a character 

 which should be used as a basis for separation of groups. However, evidence is 

 continually accumulating that indicates that separation of larger groups among 

 the bacteria solely by means of motility or lack of motility leads to a violent 

 disarrangement of natural groupings. Some non-motile bacteria present funda- 

 mental physiologies and other characters that show that they are much like 

 certain polar flagellate organisms. Such non-motile species are placed in the 

 classification used here in Order I, Pseudomonadales. However, where non-motile 

 species show fundamental physiologies and other characters more like those of 

 peritrichous species, then they have been placed in Order IV, Eubacteriales. 

 Organisms living in habitats where they are unable to use organs of locomotion 

 are usually found to be non-motile. This is very natural from the standpoint of 

 evolution. 



Some bacteria develop into trichomes, which may be defined as chains (fila- 

 ments) of bacteria where the relationship between the cells in the chain have 

 become so intimate that the cells rarely live a separate, independent existence. 

 Sometimes the cells in the chain show a differentiation into hold-fast cells and/or 

 reproductive cells distinct from the usual vegetative cells. This differentiation 

 resembles that found among the simpler algae. Because the cells in these tri- 

 chomes sometimes develop flagella that are placed singly or in a tuft near or at 

 the pole of the cell, while others develop cells with peritrichous flagella, it has been 

 felt desirable to recognize two orders among these bacteria that occur in tri- 

 chomes: Order II, Chlamydobaderiales, for the polar flagellate types and Order VI, 

 Caryophanales, for the peritrichous types. Some non-motile species occur in these 

 orders also. 



Little is known about the relationships of certain species of bacteria which 

 show a budding form of reproduction that is different from the simple cell division 

 (fission) that takes place in the four orders previously discussed. Only a few of 

 these species that reproduce by budding are well known, though some of them 

 occur abundantly in suitable habitats. Because the indications are that many 

 species of these organisms exist in nature. Prof. H. C. Douglas has set these apart 

 in a new order, Hijphomicrohiales, p. 276. Where flagellation has been observed 

 among these budding forms, it is of the polar type so that Order III has been 

 associated with Order I, Pseudomonadales, and Order II, Chlamydohacteriales, 

 in the arrangement of the 10 orders as given above. 



Until recently everyone has thought of Order V, Actinomycetalcs, as including 

 species all of which were non-motile.* However Couch, in a series of papers, 

 the latest published in 1955 (Jour. Elisha Mitchell Sci. Soc, 71, 1955, 148-155), 



* Also see footnote p. 713 for a discussion of motility in species of Nocardia by H. L. 

 Jensen. 



