Received for publication 14 Aug. 1985. Reference to brand or firm name does not constitute endorsement by the USDA over others of a similar nature not mentioned. We acknowledge the technical assistance of Anita M. Burgher, Gavin R. Graff, Sandra P. Graham, and Timothy O. Dobson, employees of the Eastern Regional Research Center. 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.