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Changes in the endogenous moisture content and biochemical viz., soluble sugar), phenols, o-phenol and peroxidase activity at different stages of adventitious rooting in auxin-treated (5 mM IBA) and non-treated miniature bud sprout cuttings of Gmelina arborea Roxb. were investigated at 0 h, 24 h, 3 days, 7 days, 2 weeks and 3 weeks of planting to elucidate the process of adventitious root formation at physio-biochemical level. Simultaneously adventitious rhizogenesis parameters viz., proportion of live green sprouts (%), callusing (%) and rooting (%) were recorded. Two weeks after planting, the marked difference for adventitious rhizogenesis was noticeable between treated and non-treated sprout cuttings. More than 20% rooting and 75% callusing were recorded in treated sprout cuttings. In contrast, only 7.4% non-treated sprout cuttings exhibited callusing. At the end of Week 3, more than 90% rooting was observed in treated sprout cuttings while it was absent in non-treated ones. All biochemicals exhibited changes in the first 24 h, indicating early incidence of consequential process(s), which influenced the differential response of cuttings to adventitious rhizogenesis in auxin-treated and non-treated state. Overall, the results indicate two possible phases of adventitious rhizogenesis – Phase I of Induction -the initial phase exhibiting low endogenous moisture and o-phenol but elevated phenol and peroxidase activity and Phase II of Initiation – the later phase coinciding with higher endogenous moisture and low phenol content and peroxidase activity. Both phases appear to be separated by an intervening unstable duration (Gap Phase of Stabilization) which may  vary among different types of cuttings/species.