Professor, Dept. of Biology, Antioch College, Ohio.
Postgraduate research geneticist.
Agriculture research technician, ARS/USDA.
Received for publication 3 Oct. 1985. This material is based on work partially supported by the Walnut Marketing Board and ARS/USDA Cooperative Agreement NO. 58-9AHZ-1-626. The use of product names does not imply endorsement by USDA. We would like to thank E. Sutter and C. Leslie for critical review of the manuscript. 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.