Received for publication 20 Jan. 1987. Contribution nos. 1888 and I-912 of Agriculture Canada, Research Station, Kentville, and Agriculture Canada, Engineering and Statistical Research Centre, Research Branch, Ottawa, respectively. Partial funding for this project was provided by the Canada/Nova Scotia Agri-Food Development Agreement. 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.