142 SOILS AND FERTILIZERS 



venient mark. Compare the intensity of color from the various 

 treatments and explain the results obtained. How may the results 

 be applied to field practice ? 



Exercise IV. — Examination of legume nodules. 



Visit fields of red clover, vetch, alfalfa, peas, etc., and with a spade 

 carefully uproot some of the plants and search for nodules. Note 

 the number, size and location of the nodules on the various legumes. 

 If suitable specimens of roots bearing nodules are found it might be 

 feasible to preserve them for exhibition purposes. They may be 

 satisfactorily preserved in glass cylinders filled with water to which 

 a few drops of formalin have been added. The cylinders should be 

 tightly stoppered to prevent evaporation. 



Exercise V. — Examination of nodule bacteria. 



If the instructor has an oil immersion microscope available, with 

 staining mixtures and other facilities for preparing slides of bacteria, 

 this would be a desirable demonstration. The pupil would then 

 gain a first hand knowledge of bacteria. Other soil organisms might 

 also be mounted for class use. 



Exercise VI. — Soil inoculation. 



If the instructor could arrange in some way to cooperate with a 

 near-by farmer in inoculating his soil by some of the means available 

 for the purpose, this would be a valuable demonstration for the pupils 

 to attend. Actually seeing a thing done is worth much more than 

 mere class room study. 



