Inhibition of Rooting of Cuttings by Gibberellic Acid: With one Figure in the Text

Gibberellic acid inhibited rooting but increased extension ofpea and bean stem cuttings. Indolylacetic acid usually had acontrary effect both on extension and on root initiation. Itwas found possible to separate the effects of gibberellic acidon extension and rooting. Small doses of gibberellic acid appliedto the bases of cuttings reduced rooting without increasingextension. Small apical doses increased extension without reducingrooting. Disbudding cuttings prevented extension, but gibberellicacid inhibited rooting of disbudded cuttings as strongly asthat of normal cuttings. It has thus been found necessary todiscard an earlier hypothesis that inhibition of rooting bygibberellic acid was a consequence of a diversion of essentialmetabolites to the extending apical regions of the cutting.The antagonism between gibberellic acid and indolylacetic acidwas non-competitive. Gibberellin A₁, known to occur naturallyin Phaseolus, was as active a rooting inhibitor as gibberellicacid. It is now believed that inhibition of rooting of cuttingsby gibberellins is a direct local effect, preventing those earlycell divisions involved in transformation of mature stem tissuesto a meristematic condition.