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A bstract. The concentrations of 3.methvl-6.methoxv-8-hydroxy-3,4-dihydroisocoumarin (MMHD) formed in carrot roots inoculated with certain fungi or treated with indole-3-acetic acid, 2,4-dichlorophenoxyacetic acid, or 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), were related to the amount of ethylene produced by the root tissue. Ethylene applied exogenously in concentrations above 0.3 ppm induced the formation of MMHD in carrot root discs. Continued production of MMHD required the continued presence of ethylene. The amounts of MMHD in the discs were reduced by CO,. an inhibitor of ethylene action, and by reduction of the partial pressure of ethylene in fungus-inoculated or 2,4,5-T-treated carrot root discs. The results indicate that ethylene is required for the induction of MMHD formation by carrot root tissue.The compound 3-methyl-6-methoxy-8-hydroxy-3,4-dihydroisocoumarin (MMHD)

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Summniarv. Gamimiia radiation at doses of 300 Krad or more inhibits the ripening of Bartlett pears (Pyrus commnunis L.). Immediately after irradiation there is a transitory burst of C2H4, which subsequently declines in fruits subjected to inhibitory doses. Ethylenie production associated with ripening begins at the same tinme in unirradiated fruits and those subjected to noninhibitory doses, but the latter produces much more C2H4 at the climacteric peak. Fruits subjected to inhibitory doses produce low levels of C2H4 unless subjected to exogenously applied C2H, whereupon they produce enough of the gas to iniduce ripening in unirradiated fruits.Pears subjected to 300 and

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Production of ethylene by fruits and leaves of the fig tree was stimulated by the application of 2,4,5 trichlorophenoxyacetic acid (20 parts per million) to levels that apparently were responsible for hastened matura tion of fruit, epinasty, and senescence of leaves.

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