Dosage effects of the tb1-ref allele on first order lateral roots. (A) Density of first order lateral roots per segment of crown root for each of three crown root segments: top (basal), middle and bottom (apical). (B) Methodology used to measure root growth rate. The unstained tissue (white) represents new root growth at 24 hours after staining roots with neutral red. (C) Rate of first order lateral root initiation, and (D) crown root elongation over a 24 hour period beginning at 34 days after transplanting (DAT). At 15 DAT, synchronously initiating crown roots were labelled (one per plant) and all root traits were quantified 20 days later. Shown is the standard error of the mean estimate. Bars with the same letter are not significantly different at α = 0.05.