TYPES OF MICROORGANISMS IN SOIL 241 



are suggested and point out any possible practical applica- 

 tions. 



REFERENCE 



LOHNIS: Laboratory Methods in Agricultural Bacteriology, p. 103. 



EXERCISE 2. A COMPARATIVE STUDY OF THE NUM- 

 BER AND TYPES OF MICROORGANISMS IN SOIL: 

 THE PLATE VS. THE MICROSCOPIC METHOD 



A. THE PLATE METHOD 



Apparatus. Sterile soil borer; sterile paper bag; sterile 

 large spatula; sterile large piece of paper; sterile paper 

 15 cm. square; 500 c.c. wide-mouthed flask containing 200 



$690,750,000 $1,342,453,982 $2,225,700,000 



Total Value of Total Value of Total Value of 



Annual Timber Cut. Mineral Output, 1911. Natural Manure. 



FIG. 54. Showing the Comparatively Enormous Value of Organic 

 Microbial Food which Should Enter the Soil. (Carver, Year- 

 book of U, S. Dept. of Agr., 1914.) 



c.c. sterile water; 90 and 99 c.c. dilution flasks (sterile 

 water); ordinary agar; sterile Petri dishes; soil (different 

 types), manure, etc. 



Each student should use one type of soil and one type of 

 manure for this experiment. Assignments will be made by 

 the instructor. The results obtained by each student 

 are to be compared with those of others. 



