Figs. 2.3-2.7. Light micrographs of longitudinal sections through tissue undergoing dedifferentiation during generation of new phellogen after mechanical wounding of bark of healthy 2-year-old peach bark. Outside bark in all figures is oriented toward top of plate. Bar = 10 m. Fig. 2.3. Section through the secondary phloem 48 hr postwounding showing mitotic activity associated with tissue redifferentiation. Cells to the left of the arrows participate in phellogen generation; cells to the right are becoming hypertrophied and developing lignified walls and intracellular suberin linings. Fig. 2.4. Section through periderm and cortex 72 hr postwounding showing two distinct tissue regions in the transition zone between healthy (left) and necrotic tissue (right). Tissue to the right of the arrows shows first positive reaction with phloroglucinol + HCl but is not yet impervious to fluid diffusion. Fig. 2.5. Section of differentiated phellogen (PG) and incipient impervious tissue (IT and arrows) 96 hr postwounding. Figs. 2.6 and 2.7. Bark tissue stained with phosphine, under bright field and the same under ultraviolet excitation, respectively, showing impervious tissue (IT), first phellem (PH), and newly regenerated phellogen (PG) 7 days postwounding. Note in Fig. 2.7 the thin suberin lining of the cells in the impervious zone (small arrows).