SUMMARY Boron is required for development of root primordia on stem cuttings of mung bean seedlings. Although exogenous boron is not required until more than 48 h after stem cuttings are placed in auxin, it may be supplied at any previous time, including during growth of the seedlings. There is a progressive loss of rooting response to auxin and boron when cuttings are aged in water prior to rooting treatment. This ageing effect is not influenced by the presence of boron but is considerably reduced by application of dilute solutions of auxin, which are themselves without effect on rooting. Cuttings prepared from seedlings grown in the presence of boron initiate fewer roots in response to low concentrations of auxin than do cuttings taken from seedlings raised in the absence of boron. Despite being required for development of root primordia, boron is antagonistic to the influence of low concentrations of supplied auxin on rooting. The possibility that boron regulates endogenous auxin levels during root development is discussed.

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SUMMARYTriiodobenzoic acid (TIBA) or morphactin (chlorfluorenol), applied to the base of the epicotyl of mung bean cuttings, inhibit root formation in the hypocotyl. Such inhibition occurs even when cuttings are supplied with auxin at the same time. Both treatments reduce the accumulation of radioactivity in the hypocotyl when [i*C]IAA is supplied to the primary leaves. Morphactin does not influence the uptake of [i^CJIAA supplied basally to cuttings, nor does it have any apparent influence on the distribution of radioactivity within the cutting. However, the extent to which [i*C]IAA moves from leaves to hypocotyl is influenced by the basal supply of auxin in which cuttings are placed. These observations are discussed in terms of the role of the leaves in auxin-induced adventitious root formation.

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