I certify that I have read this study and that in 

 my opinion it conforms to acceptable standards of scholarly 

 presentation and is fully adequate, in scope and quality, 

 as a dissertation for the degree of Doctor of Philosophy. 



s. 



Edward M. Hof firiari^ 

 Professor of Microbi 

 Cell Science 



'■^-^^Vh^.^— 



y and 



This dissertation was submitted to the Graduate Faculty 

 of the College of Agriculture and to the Graduate Council, 

 and was accepted as partial fulfillment of the requirements 

 for the degree of Doctor of Philosophy. 



December, 1982 



"Dean, 



JidyvUtJ-^ 



ege of Agriculture 



Dean of Graduate School 



