The woody part of the tree – the stem (or trunk) branches and roots are what we turn to next. What is it made of and what use is it to us?

Wood has four main constituent parts, the xylem, the cambium, the phloem and the bark.

The xylem is the main part of the woody structure of the tree; they are the tubes that transport water around. As the tree grows wider, the older central tubes gum up and become redundant. This is called the heartwood; it gives the tree its strength and flexibility. The heartwood, once a tree is felled and left to dry out is the where the main use of the tree is. The wood of the English oak (Quercus robur) is used for furniture making, house building and boat building. Oak is also much valued as firewood as is ash (Fraxinus excelsior). The ash is highly valued as it can be burned green. This is because its moisture level when unseasoned (green) is roughly the same as seasoned oak logs (about 30% moisture level) Most wood can be seasoned and as long as it is burned in an appropriate place (log burners for anything sappy and likely to spit, open fires for well seasoned hardwood)

Between the xylem and the phloem is a divider, this is called the cambium. This is where the tree grows new xylem and phloem and is therefore responsible for the widening of the tree as it grows.

Then comes the phloem, this transports the sugars created in the leaves (using photosynthesis) around the tree. This sugary liquid we know as the sap. A substance which can be tapped from a tree (especially maples and birches) and has many uses – maple syrup is a fine example of this. Birch sap is wonderfully sweet too.

The outer layer of the tree is the bark. The bark protects the tree – from the elements, pests, diseases, fungal infection, it is tough and waterproof.  It can be one of the key factors in helping to identify a tree. Especially during the winter months when all we can see are the woody parts of the broadleaf trees. Most trees bark is highly individual. The London Plane (Platanus x hipanica) has a very distinctive bark – it looks almost like army camouflage – a patchy bark of greys and greens. The walnut (Juglans regia), on the other hand has a beautiful silvery bark. The bark of the cork oak is harvested to make cork.

These four main parts of the tree can be easily seen when a tree is cut and the stump is studied – rings are clearly visible each one representing a seasons growth of the tree, but as well as these, which grow up and down the tree, there are also cells that grow in lines radiating out from the centre tree to just below the bark. These are called Rays. Excess glucose which is produced by photosynthesis within the leaves is moved through the phloem, into the rays and converted to  starch or fat. These are used by the tree to help flower and fruit production in springtime and kept in reserve in times of stress (draught, loss of leaves etc).

All in all, the wood of the tree is a fascinating structure and one which is much more complicated than it at first seems. The next time you walk past a tree stump or you pick up a log, have a look at it, marvel at its beauty, be amazed that such a seemingly simple thing can be so complicated!