Graduate Assistant. Currently Assistant Professor, Southern Expt. Station, Univ. of Minnesota, Waseca, MN 56093.
Received for publication 24 Oct. 1986. Michigan Agr. Exp. Sta. Journal no. 12125. 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.