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The effects of ethylene in lowering levels of auxin diffusing through plant tissues are well known (1, 6-8, 12, 16, 20, 22, 32 Corporation, Washington, West Virginia. The canister was constructed of degreased galvanized pipe (10 X 40 cm) with circles of screen wire in drilled pipe caps fitted with laboratory gas outlets. Teflon tape rather than oil was applied to the pipe threads to allow easy disassembly for refilling and to prevent contamination of the Purafil.In the case of plants placed in plastic bags, temperatures inside the bags were maintained at 24 C during the light phase.Unless indicated otherwise, plants were exposed to ethylene at concentrations of 25 or 100 bld/liter for an 18-hr period.The 18-hr period consisted of 6 hr of light, 8 hr of darkness, and light during the remainder of the pretreatment period.Auxin Transport. Following procedures described earlier (31), we measured auxin transport through the uppermost internode of Coleus stems. Stem segments 5 mm in length were removed from the treated and untreated plants, coated with a ring of Vaseline to prevent surface transport, and placed on glass slides. One percent agarose cylinders of a volume of 23 ,ul containing IAA-l-"4C, 5 mg/liter (32,600 cpm average per block), served as auxin donors on the physiological apical end and similar cylinders without IAA served as receivers. During the transport period the sections were in a nearly vertical position with the donor above and the receiver below. After 5 hr in a moist chamber kept in the dark, the donor and receiver cylinders and the stem sections (macerated) were placed in counting vials separately or in groups of five and frozen. The radioactivity was assayed with a Nuclear-Chicago liquid scintillation counting system following procedures described in an earlier paper (33). A second counting medium which proved to be more convenient for counting the radioactivity in aqueous samples was used in later experiments. This medium consisted of Spectrograde toluene containing the fluors PPO and POPOP mixed with Triton X-100 in a ratio of 7:6.

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