Figure 3. Chronosequence of pinning reactions in Brachystegia spiciformis throughout the growth season.

Chronosequence of pinning reactions in Brachystegia spiciformis between November (Nov) 24, 2001 and June (Jun) 22, 2002. White arrows indicate the parenchyma layer formed as a reaction to the pinning, black arrows indicate the marginal parenchyma band that forms the boundary of the 2000–2001 growth ring. On Nov 24, 2001, the wound parenchyma layer coincides with the 2000–2001 growth ring boundary, whereas on December (Dec) 7, 2001, a small number of xylem (fiber and vessel) cells is visible between the two parenchyma layers, indicating that the 2001–2002 growth season started between Nov 24 and Dec 7, 2001. The number of cells between the two parenchyma layers increases between Dec 7, 2001 and March (Mar) 2, 2002 as the tree continues its woody growth. No regular xylem cells are formed after the pinning on Mar 16, 2002, the wound parenchyma layer corresponds to the outside of the sample at this point in time, indicating the end of the 2001–2002 growth season. Note that callus tissue, as a reaction to the pinning, continues to be formed even after the end of the growth season and throughout the dry season (e.g., Jun 22). White scale-bars  = 2 mm in all photographs.