A new bioassay which employs disbudded epicotyl cuttings taken from light grown Azukia seedlings (A. angularis) was devised for testing rooting promotion activity. By use of this method, the rooting promoting principle in leaves of Portulaca grandiflora was isolated and identified with portulal which had been previously obtained. Portulal was reported as an inhibitor of rooting in etiolated Raphanus cuttings and has recently been determined to be a bicyclic diterpene containing a perhydroazulene nucleus. Portulal promoted the adventitious root formation in several kinds of plants, i.e. Azukia angularis, Vigna Catiang var. sinensis, Phaseolus Mungo and Raphanus sativus var. acanthiformis ‘Riso daikon’. The rooting process in Azukia and Raphanus cuttings seems to include at least two phases; a “preparatory phase” or a portulal- and gibberellin-sensitive phase and a “main phase” or an auxin-sensitive and portulal-insensitive phase.
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MITSUHASHI et al. (1969) studied this question.