On the shape of developing vessel elements in Fraxinus excelsior L.

In thick transverse sections through carefully sampled pieces of the developing early-wood zone of Fraxinus excelsior, the shape of the developing vessel elements is circular. On the basis of this shape and of some considerations on the mode of cellular adjustments and preliminary counts of cell-division figures in this zone, it is concluded that a twostage process for the enlargement of the vessel elements, as proposed by Zasada & Zahner (1969), is unlikely.