Adventitious root formation in Acacia baileyana F. Muell

The induction and anatomy of adventitious root formation were investigated in stem cuttings of six genotypes of Acacia baileyana treated with 0, 1,000 and 5,000 ppm indole butyric acid (IBA) in spring and autumn. Eight weeks after strike there was a highly significant effect of IBA on adventitious r oot formation, and a significant difference between genotypes in rooting ab ility. Rooting percentages were higher in autumn than in spring. Stem anato my was similar in all genotypes, irrespective of rooting ability, with a sc lerenchymatous fibre sheath located between the cortex and phloem. Stems tr eated with 5,000 ppm IBA showed statistically significant increases in orde red vascular tissue growth, cortical callus production and vascular ray dev elopment over a four week period. Adventitious root primordia were initiate d in the proliferated cortical callus, and vascular connection was establis hed via vascular rays which forced apart the sclerenchyma fibres. This ofte n occurred in the vicinity of a leaf trace.