Fig. 1.

Schematic representation of the Arabidopsis root tip. The stem cell niche, enclosed by the red line, consists of a centrally localized quiescent centre (QC) surrounded by the tissue initials/stem cells. Vascular initials are above the QC, shown in dark yellow. Flanking the QC are two types of initials: the ground tissue initials, shown in dark green that originate the cortex and endodermis, and the epidermis/lateral root cap initials, shown in dark blue. Below the QC, shown in dark pink, are the columella initials.