Dot closure
As Tüpfelverschluss is at Court stipple the application of the torus to the pore denotes the result of pressure change in the cell lumen may occur.
root cause
If, in the course of the heartwood formation or drying of the wood after felling of a tree in a decrease of wood humidity , this may be a closure of the court pits entail. Since the pelvic margo has a certain flexibility due to its fibrillar structure, the torus can attach itself to the edge bulge in the event of pressure changes or air penetration into the cell lumen and thus close the porus. The anatomical prerequisite for the possibility of the spot closure is the presence of a torus. The phenomenon is therefore limited to the pits of the Pinaceae .
Influencing factors
From a chemical point of view, the surface tension and the adhesion are important influencing factors on the spot closure. The lower the surface tension of the liquid from which drying is carried out, the lower the tendency towards the spot closure. Since the adhesion of the torus to the edge bead is based on hydrogen bonds , drying based on certain organic solutions that are not capable of forming hydrogen bonds prevents a permanent spot seal.
Bordered pits in the late wood of conifers have compared to spotting in early wood a smaller diameter, a thicker and denser torus Margo. Due to the higher mechanical stability of the pitting membranes, late wood pits have a lower tendency to close.
During the heartwood formation there is an encrustation with resin acids , mono terpenes , fatty acids and other extractives . This increases the spot closure in two ways: On the one hand, the extract substances reduce the diameter of the spot pores; on the other hand, they act as a kind of adhesive that improves the bonding of the torus to the edge bead.
Influence on impregnability
A number of wood technological processes, e.g. Eg in the fields of wood protection , the wood modification or pulp manufacturing, depend on the treatability of the wood from. The disadvantage here is that the flow of liquids through closed pits is severely restricted. However, it is not entirely excluded. Two flow paths are possible:
- The first path runs through the openings of the margin and then between the torus and the rim into the cell lumen of the neighboring cell. The width and the tightness of the contact zone between the torus and the edge bead represent the essential factors that influence the flow through this path. In most cases this contact zone is relatively impermeable. In some species a layer of warts prevents a tight seal.
- The second path leads directly through small openings in the torus.
The spot closure is not an irreversible process. When the wood is re-moistened, closed pits can open in the sapwood as a result of the loosening of hydrogen bonds . Pressure impregnation with water-based wood preservatives makes use of this.
literature
- Andreas Bresinsky , Christian Körner , Joachim W. Kadereit , Gunther Neuhaus , Uwe Sonnewald : Strasburger - textbook of botany . Founded by Eduard Strasburger . Spektrum Akademischer Verlag, Heidelberg 2008 (36th edition) ISBN 978-3827414557
- Nicholas, DD; Siau, JF (1973): Factors influencing the treatability of wood. In: Nicholas, DD (ed.): Wood deterioration and its prevention by preservative treatments. II Preservatives and preservative systems, Syracuse Univ. Press, Syracuse
- Rosenthal, M; Baucker, E .; Bues, CT (2011): Wood structure and impregnability. About the influence of the microstructure of wood on the penetration behavior of liquids. , P. 6. ff.
- Siau, JF (1984): Transport processes in wood. Springer Verlag, Berlin, Heidelberg, New York, Tokyo
