Present address: Department of Horticulture, University of Kentucky, Lexington, KY 40546.
Present address: Plan Granjero, Avda. Uruguay 823, Montevideo, Uruguay.
Received for publication July 6, 1982. Journal article number 10491 of the Michigan 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.