Received for publication January 17, 1980. Research supported by the College of Agricultural and Life Sciences, University of Wisconsin, Madison, and by USDA Science and Education Administration, Agricultural Research.
The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper must therefore be hereby marked advertisement solely to indicate this fact.
Research Assistant, Research Horticulturist, USDA/SEA/AR, and Assistant Professor, respectively.