No. 615] BACTERIAL PHY LOG EX Y 237 



of names to be recognized as valid for the genera of Un- 

 order. They have also suggested that these genera be 

 grouped in seven families. Altogether twenty-eight 

 genera are recognized. It should be possible, if adequate 

 knowledge is at hand, and the Eubacteriales constitute 



show their probable and their possible relationships, and 

 perhaps gain some knowledge thereby of their origin and 

 evolution. 



From the standpoint of the evolution of bacteria we 

 are much interested in the organisms which can live and 

 grow in the total absence of organic matter, those which 

 utilize inorganic substances exclusively in the manufac- 

 ture of their own food, in short, those bacteria which are 

 strictly prototrophic. 



Let us consider the possible sources of the various ele- 

 ments needed in the building up of the primitive bacterial 

 protoplasm. We have no reason to suppose that such 

 primitive bacterial protoplasm differed in any marked 

 degree from the protoplasm of modern forms. Such or 

 ganisms must have available carbon, hydrogen, nitrogen, 

 oxygen, sulphur, phosphorus and iron, with small quanti- 

 ties of a few other elements. Upon the earth before the 

 advent of other plant life, the carbon necessary for 

 growth would probably be secured from carbon dioxide, 

 or possibly from methane or carbon monoxide ; the hydro- 

 gen was undoubtedly present in abundance in water, 

 perhaps traces also of the free element, of methane, or 

 of ammonia may have been available ; the nitrogen was 

 probably present in sufficient quantities either as ammonia 

 or as nitrates, and of course in the form of less available, 

 relative! v inert, gaseous nitrogen; the sulfur probably 

 existed as sulfids, sulfates, and free sulfur; the phos- 

 phorus was probably found in phosphates and the iron in 

 both ferrous and ferric condition. It is evident that ele- 

 ments and compounds were present in abundance and 

 variety, but not in the form of organic compounds. All 

 modern living organisms are divided into those which 



