CHAPTER IX 



The Evolutionary Relationships of Bacteria 



A: MORPHOLOGICAL EVIDENCE IN SYSTEMATICS 



(3, 7, H) 



WHEREAS in Other biological sciences the study of morphology and 

 of systcmatics has, for the most part, been conducted by the same 

 people, this is by no means true of bacteriology. Although 

 acknowledging the importance ot morphological studies, the systematists 

 have, with a few, notable exceptions, rarely been engaged in them. Many 

 have indeed failed to acquire sufficient familiarity with the subject to enable 

 them fully to understand or evaluate cytological information where it is 

 available. 



On the other hand, many morphologists have been so closely engaged in 

 the study of a single character, in a very small range of morphological types 

 of bacteria, that they have been equally badly placed to attempt the tormulation 

 of a general scheme. 



There is no doubt, however, that one of the most valuable contributions 

 of the study of bacterial cytology to biological science is the information 

 which it affords upon numerous, vexed problems of systematics. By its use 

 an evolutionary system of classification, comparable with, and relatable to 

 that employed in all other groups, may be applied to bacteria. 



This system is the main subject of another book (Bacteria, 1952 ; published 

 by E. & S. Livingstone Ltd.), but it is appropriate that its cytological aspects 

 should be discussed here. 



B: PREVIOUS SCHEMES OF CLASSIFICATION 

 (i, 4, 6, ,S) 

 The best known classification ot bacteria in current use is that ot Bergey's 

 Manual (6th Ed., 1948). The major defect of this system is that it is manifestly 



