Present address: Dept. of Hort. and Landscape Architecture, Washington State Univ., Pullman, WA 99164-6414.
Dept. of Statistics.
Received for publication 2 Feb. 1984. This investigation is part of a thesis submitted by the senior author in partial fulfillment of the requirements for the PhD degree. 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.