Ten trees of mountain birch (Betula tortuosa Ledeb, now Betula pubescens subsp. czerepanovii) with an average age of 39 years were sampled in northern Lapland in Finland. The average green density of wood was 589 kg/m3 and that of bark 941 kg/m3. The basic densities were 520 kg/m3 and 559 kg/m3, respectively. The basic density increased only little from the pith to the surface. In contrast, the number of bars in the perforation plates of the vessels increased considerably in the same direction. The average number of bars was 17.3.
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