Received for publication 19 Nov. 1987. The investigation reported in the paper (87-10-242) is in connection with a project of the Kentucky Agriculture Experiment Station and is published with the approval of the Director. This material is based upon work supported, in part, by the U.S. Department of Agriculture, Agreement no. 59-2213-1-717-0 (Competitive Research Grants Program). 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.