A 30 x 30 mm segment of bark was removed from the wooden cylinder of a horse chestnut (Aesculus hippocastanum L). On August 10, 2006, 8 wounds were inflicted upon the trunk and samples were taken weekly until September 28, 2006. Histological changes were examined in the bright field and UV light, using a Nikon Eclipse E800 microscope. The progression of occurrences was analyzed chronologically. On the 7th day after the wound infliction, there was no change on the wound surface. 14 days after the infliction, the callus tissue started to develop on the wound surface. This tissue consisted of 3 anatomical layers; 1st directly on the exposed wood, 2nd on the surface of the callus tissue, and 3rd in the middle part of callus tissue. The presence of suberin could already be observed. On the 21st day after the infliction, the cells in the middle part of the callus tissue were arranged in proper radial rows; thick cell walls started to form on the surface. In the middle layer, there was evidence of cell hyperplasia and hypertrophy. On the 28th day after the infliction, formation of new cork cambium could be observed right under the ligno-suberin layer in the tangential direction. On the surface of the callus tissue, some deposits of lumen cells were found, which together with the ligno-suberin layer, act as protection. On the 35th day after the infliction, the ligno-suberin layer was clearly visible. In the middle layer of the callus tissue, the cells started to lignificate in nests. On the 42nd day after the infliction, formation of vascular cambium and thickening of cell walls in the callus tissue was observed. On the 49th day, the process of division in the vascular cambium was no longer observed. Under the ligno-suberin layer, new cork cells were formed that were also suberized. The lignification of tissue cells over and under the cambium progressed as well. Changes in wounded tissues had been occurring until September 28, 2006. At that time period the phytological activity of meristems under normal growth conditions at this latitude already ends. The key event in the post-wound reaction was the formation of ligno-suberin layer that protects the wounded area from drying out and from fungus infection.