Received for publication January 3, 1974. Journal paper No. 2000 of the Virginia Polytechnic Institute and State University.
Department of Horticulture.
Grateful acknowledgement is made for the assistance of C. Y. Kramer, Professor of Statistics, V. P. I. and S. U., Blacksburg, for experimental design and analysis of data. The partial support of the Virginia Agricultural Foundation was greatly appreciated.