Figure 1.

Root Growth Dynamics at Steady State

In the laboratory frame (left), where growth pushes the tip downward, the boundaries (orange lines) between zones move, keeping pace with the root tip. In this frame, the boundaries pass by cells (blue and red ovals) and by the spatial coordinates (mustard-colored scale). In the root-tip frame (right), where growth apparently pushes material upward, the boundaries remain at the same coordinates and are traversed by cells. The tip (in fact, the quiescent center) is assigned x = 0. Reference values (microns) on the scale are approximate.