Received for publication 15 Oct. 1983. The authors thank R. Forrester, CSIRO Divison of Mathematical Statistics, for his statistical advice. The use of the growing system NFT in this work does not imply that it is a fully developed method for commercial use with roses. 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.