Received for publication 9 Jan. 1984. Utah State Expt. Sta. Journal Article No. 2921. The author thanks the Dave Wilson Nursery of Hughson, Calif, for providing the carrots. The use of Roger Wyse's facilities for this study is also gratefully acknowledged. 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.