244 THE AMERICAN NATURALIST [Vol. LIT 



Some forms have developed the ability to produce endo- 

 spores (family Bacillacea) and seem to comprise a 

 closely related group of genera whose relationship to the 

 more primitive types is somewhat problematic. Another 

 well-marked group of bacteria includes the large series 

 of (usually) gram-negative bacteria that produce no 

 spores. These may be included in a family Bacteriacecs. 

 With the exception of polar flagella, there is no very 

 marked difference between the Pseudomonas forms and 

 the Proteus types. It is quite possible that they are 

 closely related. The cocci apparently form another 

 homogeneous group, the Coccacem. The affinities of the 

 group may be sought in several places. For example, 

 there is apparently very close resemblance culturally and 

 physiologically between the chromogenic cocci and the 

 chromogenic rods closely related to the genus Bacterium; 

 the organism usually termed Bacillus prodigiosus (Ser- 

 ratia marcescens) is remarkably near certain red cocci as 

 Rhodococcus roseus. The possibility that there is a rela- 

 tionship between the Nitrosococcus and Micrococcus has 

 already been pointed out. Then there is a decided rela- 

 tionship evident between the aciduric bacilli and the genus 

 Streptococcus. All of these origins are possible; if all 

 these relationships are true, the group Coccacece must be 

 regarded as heterogeneous, that is, polyphyletic. 



The group containing the tubercle bacillus {Mycobac- 

 terium) and diphtheria bacillus (Corynebacterium) 

 shows undoubted relationships to the order Actinomy- 

 cetales. If they have no common origin with other 

 genera of the Eubacteriales they should be included in the 

 order Actinomycetales. However, there is decided evi- 

 dence of relationship through Leptotrichia and perhaps 

 Erysipelothrix to the lactic acid bacteria. If this is a 

 valid relationship it would indicate that the Actinomy- 

 cetales are an offshoot of the Eubacteriales, or at least 

 have a common ancestry. 



The various relationships illustrating the probable 

 phylogeny of the class Bacteria is illustrated in the ap- 



