Present address: 360 Agricultural Hall, Dept. of Horticulture and Landscape Architecture, Oklahoma State Univ., Stillwater, OK 74078.
Received for publication 29 Mar. 1985. Paper No. 9806 of the J. Ser. of the N.C. Agr. Res. Serv. (NCARS), Raleigh, NC 27695-7601. From a thesis submitted by the senior author in partial fulfillment of the requirements for the PhD degree. The authors gratefully acknowledge the technical assistance of C.G. Giles and R.T. Novitzky. Use of trade names in this publication does not imply endorsement by the NCARS of the products named nor criticism of similar ones not mentioned. 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.