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The aim of this study was to compare the structure of beech juvenile and mature wood in relation to wood density. The comparative analysis between juvenile and mature wood examined the diameter of vessels, the width and height of pith rays, and the number of vessels and pith rays per 1 mm 2 . The results show that the average vessel diameter as well as the width and height of pith rays reach statistically lower values in juvenile wood than in mature wood. On the other hand, no significant difference between the two types of wood has been found in terms of the frequency of vessels per 1 mm 2 . Having said that, the difference in the frequency of rays per 1 mm 2 between juvenile and mature wood is far from being negligible; juvenile wood has three times as many pith rays as mature wood. The density of juvenile wood is higher (ρ 12 = 726.07 kg/m 3 ) than the density of mature wood (ρ 12 = 701.50 kg/m 3 ).

Wood is a hygroscopic material that is affected by shape changes. The aim of this study was to analyse the variability of wood swelling in the individual anatomic directions. Wood swelling was examined on a sample tree containing compression wood. With regard to the presence of compression wood, the sample tree was divided into the following three zones: the compression wood zone (CW), the opposite wood zone (OW), and two side wood zones (SWL and SWR). The results show that the wood containing compression wood swells less at the transverse plane (in the radial and tangential direction). Conversely, the swelling of compression wood in the longitudinal direction is higher. The same proportion was established in the swelling coefficient that grew proportionally to the increasing wood density in all anatomic directions. The proportion of compression wood manifested its effects in different ways. Transversely (in the radial and tangential direction) the swelling coefficient decreased proportionally to the increasing percentage of compression wood, longitudinally, however, the opposite was the case.