Distribution of vessel ends in stems of some diffuse- and ring-porous trees: the nodal regions as “safety zones” of the water conducting system

We report measurements of the number of vessels ending within the nodes in comparison with that in the internodes. Such measurements have been carried out during autumn 1982 and 1983 in 1-year-old twigs of three species with diffuse-porous wood (Vitis vinifera L., Populus deltoides Bartr. and Olea europaea L.) and three ring-porous trees (Juglans nigra L., Castanea sativa Mill., Sophora japonica L.). In all three species with diffuse-porous wood, a significantly higher percentage of vessels ending in the nodes (at the leaf gap) was recorded when compared with that in the internodes. No significant differences were found between nodes and internodes in this respect in ring-porous trees. Since vessel ends are capable of screening out gaseous emboli and/or particles bigger than 1 μm in diameter, we interpret the nodes of diffuse-porous trees as stem zones providing safety for the water conducting system. The reason why ring-porous trees are likely not to need such 'safety zones' is also discussed.