EVOLUTION OF BACTERIA 85 



The great geologic antiquity even of certain lower forms 

 of bacteria which feed on nitrogen is proved by the discovery, 

 announced by Walcott^ in 191 5, of a species of pre-Palaeozoic 



ABC 



'■■^r -^ 



V-- . ' 5»/| 



N 



D E F 



Fig. II. Fossil .\nd Living B.\cteri.\ Compared. 



Extremely ancient fossil bacteria (.1) compared \vith similar t\-pcs of Ii\-ing bacteria 

 {B-F). 



A. Fossil bacteria from the pre-Cambrian Xewland limestone (Algonkian), after Walcott. 



B. E.xisting nitrifying bacteria found in soils — the arrow indicates a chain series similar 



to that of Walcott's fossil bacteria. 



C. A more complex type of nitrifying bacteria found in soils. 



D. Nitrogen-fixing bacteria from the root nodules of legumes. Note the granular struc- 



ture of the supposed "chromatin." 



E. Denitrifying bacteria found in soil and water. 



F. Bacteria stained to bring out the chromatin granules or "nuclei" in the centre of 



each rod-like bacterial cell. 



fossil bacteria attributed to '''Micrococcus,'' but probably 

 related rather to the existing Xitroso coccus, which derives its 

 nitrogen from ammonium salts. 



These fossil bacteria were found in a section of a chlorophyll- 



■ Walcott, Charles D., 1915, p. 256. 



