Visiting Professor from Department of Horticulture and Forestry, Cook College, Rutgers University, New Brunswick, NJ 08903.
Plant Physiologist. California Agr. Expt. Sta., Davis, CA 95616.
Received for publication July 1, 1982. 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.