Received for publication April 9, 1969. Published with the approval of the Director of the Michigan Agricultural Experiment Station as Journal Article No. 4679.
Assistant Professor, Department of Horticulture.
Presently employed as Research Biologist, American Cyanamid Co., Princeton, New Jersey.
The authors wish to express appreciation to District Horticulturists W. S. Carpenter, C. D. Kesner, W. J. MacLean and J. E. Lincoln and County Extension Agents A. R. Earl, L. W. Stebbins and W. L. Rushmore for aid in establishing research areas in commercial orchards. The financial support of the E. I. Dupont de Nemours and Company, Industrial and Biochemicals Department is also gratefully acknowledged.