Received for publication 4 Mar. 1985. Paper no. 9744 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh. The technical assistance of Mitchell Bennett, William Newall, James Griggs, and Steve Worthington is appreciated. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact.
Associate Professor, Dept. of Horticultural Science.