Fig. 2.

Representations of 3-D distribution of lateral roots. Since lateral roots originate from the pericycle cells out of the phloem, the phloem bundles are considered as the reference for the lateral roots. One phloem bundle is arbitrarily taken as the starting point. The others are labelled clockwise, being identified by their radial angles from the start point. In the longitudinal direction, the position of a lateral root is noted by its distance from the base of the segment. Thus the 3-D position of any lateral root is defined by a radial angle in transverse section and the axial distance to the segment base.