Received for publication 3 Mar. 1986. Published with the approval of the Director of the Arkansas Agricultural Experiment Station. 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.
Graduate Assistant, Dept. of Horticulture. Present address: Dept. of Horticulture, Univ. of Maryland, College Park, MD 20740.