BACTERIAL PHYLOGENY AS INDICATED BY 

 MODERN TYPES 1 



DR. R. E. BUCHANAN 

 Iowa State College 



The importance of the group we call bacteria in any 

 theories concerning the origin and evolution of life on our 

 planet is well shown by several recent writers on the sub- 

 ject, notably Jensen (1909), Osborn (1916), and Kligler 

 (1917). In each case, however, there are certain misin- 

 terpretations of our knowledge of the modern bacteria 

 and their function which go far to invalidate, or at least 

 to weaken, the specific conclusions which they reach with 

 reference to the types of primitive bacteria. 



In our search for hints as to ancestral types by in- 

 vestigation of modern species of bacteria we must hold in 

 mind that although present-day bacteria approach most 

 closely to what we conceive must have been primitive life, 

 nevertheless and for this very reason the group of modern 

 bacteria must have the longest evolutionary history of 

 any existing' group. That any modern species closely 

 resembles the original type is therefore not extremely 

 probable. It can not be too often emphasized that in 

 speculations concerning evolutionary history based upon 

 modern forms with no adequate fossil ancestral types we 

 must deal only with the tips of the ultimate twig 

 branches of the evolutionary tree. By a careful com- 

 parison of the surviving forms we may gain a knowledge 

 of their probable relationships, but it should be remem- 

 bered that in no case this relationship is that of parents 

 and offspring, but that of brother- and cons ins. Perhaps 

 we may speculate upon the probable arrangement of the 

 branches of the evolutionary tree that have disappeared 



