58 PRINCIPLES OF SOIL MICROBIOLOGY 



gators 14 deny the formation of symplasm by Azotobacter; this is 

 looked upon as a stage of gradual autolysis of the cell membrane 

 rather than a stage of reproduction. Henrici 15 demonstrated that bac- 

 terial cells undergo metamorphosis during the growth of a culture, 

 similar to that exhibited by cells of a multicellular organism; each 

 species presents three types of cells: a young form, an adult form and 

 a senescent form; the variations depend upon the rate of metabolism. 

 Classification of bacteria. This is not the place to discuss the value 

 of the different systems of classification of bacteria. It is sufficient to 

 call attention to the systems of Migula, Lehmann and Neumann and 

 to that proposed by the Committee on Classification of the Society 

 of American Bacteriologists, and incorporated in Bergey's Manual. 16 

 One may conveniently use here Migula's classification, with slight modi- 

 fications, especially in the case of the Bacteriaceae, which are more 

 commonly divided on the basis of spore formation. 



I. Simple and undifferentiated forms, not forming any threads and not branch- 

 ing under normal conditions. Order Eubacteria. 



1. Cells mostly spherical, rarely rod-shaped, Coccaceae Zopf emend. 



Migula: 



(a) Division in one direction, frequent formation of chains, 1. Strep- 



tococcus Billroth. 



(b) Irregular division in all directions; cells occur singly, in pairs or 



clumps, but not in chains, 2. Micrococcus Cohn. 



(c) Division in three directions leading to packet formation, 3. 



Sarcina Goodsir. 

 Planostreptococcus, Planococcus, Planosarcina include similar 

 but flagellated group. 



2. Cells mostly rod-shaped, rarely spherical or curved, Bacteriaceae Zopf 



emend. Migula: 



(a) No endospores formed, 4. Bacterium Cohn. 



(b) Endospores formed, 5. Bacillus Cohn. 



(c) Cells with polar flagella; endospores rarely formed, 6. Pseiulo- 



monas. 



3. Cells mostly curved or spiral, rarely spherical or rod-shaped, Spirilea- 



ceae Migula: 



(a) Cells comma-shaped, 7. Vibrio Midler emend. Loftier. 



(b) Cells rigid, spiral shaped, 8. Spirillum Ehrenberg emend Loffler. 



(c) Cells flexible, spiral shaped, 9. Spirochaeta Ehrenberg. 



14 Beauverie, J. Le symplasme bacterien existe-t-il? Cas de l'azotobacter. 

 Compt. Rend. Acad. Sci. 180: 1792-1794. 1925. 



15 Henrici, A. T. On cytomorphosis in bacteria. Science 61: 644 646. 1925. 



16 Winslow, C.-E. A., Broadhurst, J., Buchanan, R. E., Krumwiede, C, Rogers, 

 L. A., and Smith, G. H. The families and genera of the bacteria. Jour. Bact. 

 6: 191-229. 1920; also Ibid. 2: 505. 1917; Bergey, 1924 (p. x). 



