24 



Historical 



Cutler on the soil protozoa and of Pringsheim, Robbins, Esmarch, 

 Chodat, and Bristol on the soil algae, opened new fields for the 

 study of the microbial population of the soil. These investigations 

 and numerous others soon following broadened the subject of soil 

 microbiology and reaffirmed the great abundance in the soil of 



Fig. 16. 



E. B. Fred made a comprehensi\e stud>' of the root-nodule bacteria 

 of leguminous plants. 



various groups of organisms besides the bacteria. In spite of the 

 broadened scope of investigations, however, the bacteria were not 

 neglected. It is sufficient to mention the work of Topping, Lochhead, 

 Conn, and Winogradsky on the general composition of the bacterial 

 population; of Ford and N. R. Smith on the spore-forming bacteria; 

 of Hutchinson and Clayton, Krzemieniewska, Issatchenko, and others 

 on the aerobic cellulose-decomposing bacteria; of Khouvine, Pochon, 

 and Fred on the anaerobic cellulose-decomposing bacteria; of Lip- 

 man, Waksman, and Starkey on the sulfur-oxidizing bacteria; of 

 Lohnis, Hansen, Fred, Baldwin, McCoy, Stapp, and others on the 



