Fig. 2.

Stele structure for each day of pioneer root growth (left column) and the area of xylem pole, demonstrating tracheary elements (TEs; empty cells) and primordial differentiating TEs (with nuclei; only those with TUNEL-positive reaction are marked) in root of different ages. Only cells from the meristematic zone are presented at day 1 (in the right column). Both the procambial region of the outermost xylem initials and the first cambial cells are indicated by the dashed line. PX, protoxylem; MX, metaxylem. Note: the figure is not drawn to scale.