Natural wood colouring process in Juglans sp. (J. nigra, J. regia and hybrid J. nigra 23 x J. regia) depends on a five phenolic compounds accumulated in the transition zone between sapwood and heartwood. In Trees : Structure and Function. - Berlin : Springer - Verlag. ISSN 0931-1890, 1998, roč. 12, č. 5, s. 258-264.