Experiments were carried out on isolated stem segments of ash collected from natura! conditions during the winter dormancy season. In order to stimulate cambial activity and vessel difTerentiation the internodes were treated with auxin. The duration of treatment with auxin was difTerent in the particular experimental variants. It appeared that auxin was necessary not only for induction of vessel difTerentiation but also du ring their maturation. The results are discussed on the basis of Sachs· (1981) hypothesis
