1. Zone of Zone of differentiation Zone of elongation
Anatomy of the Arabidopsis Root Tip:   The architecture of the root of this model plant is very simple (Fig. 1 below). Each of the tissues outside the vascular bundle (the pericycle, the endodermis, the cortex and the epidermis) are only one cell layer thick.   The columella is one of the gravity sensing organs of the plant. C1-C4 below refer to specific cells in the columella.   The QC is the quiescent center. Quiescent means quiet, referring to the fact that these cells seldom divide. The cells next to the QC do divide frequently and are the stem cells of the root. The cells above the QC give rise to the epidermis, cortex, endodermis, pericycle and the vascular bundle. The cells below the QC give rise to the root cap, including the columella.  
Zone of
Zone of differentiation
Zone of elongation
Zone of cell division
Figure 2. Detection of GUS expression in an LHA2:GUS line
Figure 1. Tissues of the Arabidopsis root