446 R. S. BREED, H. J. CONN AND J. C. BAKER 



of many bacteria-^salt water, fresh water and soil — has presented 

 fairly uniform conditions throughout long geologic periods. 

 Yet we can hardly assume that all of the primitive types of 

 bacteria are still living. In fact, it would be more in harmony 

 with what is known of the persistence of species and genera among 

 higher forms of life — especially when the very brief life-cycle of 

 bacteria is considered — to assume that the primordial types are 

 all extinct. This idea seems to have been overlooked by Kligler 

 in his recent paper (1917). Jensen in general kept the fact 

 well in mind that he was dealing with end-products only; yet he 

 also overlooked it at times, and failed to incorporate it into the 

 diagram which he drew up to show the relationships of the 

 different groups. In this diagram Jensen places the cephalotri- 

 chic organisms at the base of three main lines of development 

 instead of representing them as a main branch coordinate with 

 the peritrichic forms. Similarly Kligler makes no attempt to 

 indicate that the Pseudomonas line of development appears to 

 be as diverse as any other line; and has even indicated modern 

 pathogenic forms (diphtheroids and albococci) as the ancestors 

 of micrococci, a group which presumably includes the primitive 

 cocci of soil. 



This fallacious line of reasoning has led to certain question- 

 able conclusions as to the relationships of bacteria, some of which 

 have even been accepted by the committee on classification. 

 The best way to point out this weakness in their report is to 

 examine critically the different groups which they propose to 

 establish. 



The orders. The committee on classification recognizes four 

 orders, Myxobacteriales, Thiobacteriales, Chlamydobacteriales, 

 and Eubacteriales, together with an appendix, Spirochaetaceae. 

 It is to be noted that they place Eubacteriales last, although it 

 contains the simplest forms, while it is customary to arrange 

 classifications in such a way that the simpler groups are placed 

 at the beginning. The committee, indeed, has used the latter 

 plan in arranging the classification of the Eubacteriales, as their 

 first family, Nitrobacteriaceae, is the one they consider most 

 primitive. In this respect there is an evident inconsistency 



