Received for publication 5 May 1986. We express our gratitude to Gene Mero for bringing to our attention the need for this study, Kent Bradford for reviewing the manuscript, Oswaldo Ochoa for technical assistance, and Kathy Hykonen for typing the manuscript. Research supported by the California Celery Research Grant QUI-7-86 and BARD Grant #1-483-82. 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.