Dosage effects of the tb1-ref allele on second order lateral roots. (A) Total number of second order lateral roots per unit length of crown root for each of three crown root segments: top (basal), middle and bottom (apical). (B) Density of second order lateral roots per unit length of first order lateral root. Measurements were performed at 34 days after transplanting (DAT) on crown roots synchronously initiated at 15 DAT (n = 12). Shown is the standard error of the mean estimate. Bars with the same letter are not significantly different at α = 0.05.