Figs. 9 and 10. Light micrographs of transverse sections of wounded bark during the process of generation of new phellogen. Bar = 10 microns. Figs. 9 and 10 show bark tissue stained with phosphine, under bright field and the same under ultraviolet excitation showing differentiated phellem (PH) and cells of the impervious zone (IT, its internal boundary delimited by arrows) exhibiting cell wall lignification and suberin linings (small arrows in Fig. 10).