Graduate Research Assistant. Present address: Dept. of Plant and Soil Sciences, Univ. of Massachusetts, Amherst, MA 01003.
Graduate Research Assistant. Present address: Dept. of Horticulture, The Ohio State Univ., Columbus, OH 43210.
Associate Professor. Present address: Dept. of Horticulture, Univ. of Wisconsin, Madison, WI 53706.
Received for publication 22 July 1986. Scientific Article no. A-4449. Contribution no. 7440 of the Maryland 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.