Abstract
The bark structure of Quercus faginea Lam. in trees 30-60 years old grown in Portugal is described. The rhytidome consists of 3-5 sequential periderms alternating with secondary phloem. The phellem is composed of 2-5 layers of cells with thin suberised walls and narrow (1-3 seriate) tangential band of lignified thick-walled cells. The phelloderm is thin (2-3 seriate). Secondary phloem is formed by a few tangential bands of fibres alternating with bands of sieve elements and axial parenchyma. Formation of conspicuous sclereids and the dilatation growth (proliferation and enlargement of parenchyma cells) affect the bark structure. Fused phloem rays give rise to broad rays. Crystals and druses were mostly seen in dilated axial parenchyma cells. Bark thickness, sieve tube element length, and secondary phloem fibre wall thickness decreased with tree height. The sieve tube width did not follow any regular trend. In general, the fibre length had a small increase toward breast height, followed by a decrease towards the top. Fibre width decreased with height in most of the cases, but in some trees a slight increase was noticed at the top.
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