Tree trunk structure

  1. Marrow
  2. Growth Rings
  3. Wood or Xylem
  4. Vascular cambium
  5. Phloem
  6. Bark or Rhytidome

The trunk has a bearing function and its system is based on the alternation between nodes and internodes that transports water and mineral salts from the roots to the leaves.

In all wooden plants we can clearly see different layers: around the marrow we can see the  growth rings that grew one after the other as the plant gets old.

The vascular cambium is responsible for the creation of new tissues towards the inside where we can find the Wood or Xylem, whose main function is the bearing and transport of the raw sap from the roots to the leafage (Phloem) or protecting the Bark or Rhytidome.

Looking at the final part of the transversal section of the trunk we can see a dark central part, the duramen, surrounded by a total white or more often white with yellow or brown shades band called alburnum. The alburnum is composed of a young vascular cambium (new wood) which contains the alive cells (parenchymal, epithelial etc.) of the growing tree. Therefore the whole wood is alburnum at the beginning, the most internal parts of the wood start to stop the conduction of  the cells with ist growth and ageing.


Macroscopic Structure

The wooden fibres


The wooden fibres or tracheids, are the main cells that form the macroscopic structure of the wood.

These hexangular cells, whose diameter is between 20 and 40 micrometre, have a longitudinal typical elongated form. They are between 2 and 4 mm long and their walls are made of layers of cellulose fibres.

The moisture content of the common green wood depends on the environment conditions, values up to 200% can be reached because of the its highly porous nature. Their elongated form makes the longitudinal contraction negligible, whereas in the transversal direction it can reach also the 10-15%.



Growth Rings

Spring wood and late wood


Inside the trunk we can clearly see two kinds of wood: SPRING and LATE. The first one ensures a quick sap transport at the beginning of the growing season, whereas the second one formed during the summer time has mainly a bearing function. Moreover it has a higher resistance, density and parameter values for the wood contraction and swelling than the spring wood. Because of the uninterrupted vegetative activity, the rings seldom or even do not appear at all in evergreen trees in tropical forests.