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. 



Ronald G. Wolff 



Associate Professor of Zoology 



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. 



^,7y*-xr4 



)seph^. Davis 

 ^rofessor of Botany 



This dissertation was submitted to the Graduate Faculty of the 

 Department of Zoology in the College of Liberal Arts and Sciences and 

 to the Graduate School and was accepted as partial fulfillment of the 

 requirements for the degree of Doctor of Philosophy, 



May 1991 



Dean, Graduate School 



'^l. 



'■\: 



