This research was supported by Purdue Univ. Agricultural Experiment Station Program funds, Binational Agricultural Research and Development Fund US-239-80, United States Department of Energy DE 13109, and National Science Foundation grant NSF PCM-8400133. Journal paper 10,769 of the Purdue Univ. Agricultural Experiment Station. We gratefully acknowledge M.L. Binzel, J.M. Clithero, E.A. Frankenberger, S. Handa, F.D. Hess., S.R. Hess, S.M. Jain, A. Kononowicz, P.C. LaRosa, G.J. McClatchey, D. Rhodes, N.K. Singh, and A.A. Watad for their contribution to this research and the Electron Microscopy Center in Agriculture at Purdue Univ. for use of the scanning electron microscope. Electron micrographs were provided by M.L. Binzel.