The structure of cambium and latest differentiated phloem cells affect the wood/bark adhesion evaluated by shear strength. The thesis evaluates shear strength on wood/bark interface in two anatomical directions and two tree species – beech (Fagus sylvatica L.) and oak (Quercus petraea (Matusch.) Liebl.) during one year. Results showed that dormant and growing season, moisture content (sapwood, heartwood and phloem), tree species and also the loading direction belong to the most important factors affecting the shear strength or wood/bark adhesion. The lowest values of shear strength were observed in growing season in fresh and dry state at both of tree species. The values of shear strength of beech increased about 190 % in both anatomic directions. The values of shear strength of oak showed differences between loading directions, what represented increase of 184 % in longitudinal direction and more than 260 % in tangential direction. The shear area in dormancy was in zone of the latest created non-collapsed late sieve-tubes. The shear area in growing season was in cambial zone at beech or in latest early vessels at oak. The shear strength is also considerably affected by different structure of thin and wide phloem rays or sclereids.