Received for publication November 3, 1982. Supported in part by a grant from the N.S.W. State Pollution Control Commission. The assistance of Roslyn Avery, Marina Ivinskis, Elizabeth Kershaw, and David Roshier is gratefully acknowledged. Thanks are also due to Tom Saltau and Oliver Shaul for permission to use their vineyard for this work. 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.