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Like the roots, trunks and branches have three functions. They, too, store sugars in the dormant period. They act as highways, transporting water and nutrients from the roots to the leaves, and energy-rich sugars from the leaves to other parts of the tree. And they ensure that the leaves have a high and wide distribution, in order to gain as much exposure to sunlight as possible. If you look at a cross-section of a trunk or branch, you’ll see the familiar annual rings, of which each ring indicates a year’s growth. Fast-growing trees have thick annual rings and slow-growing trees demonstrate thin ones. A 100-year-old bonsai with a 5cm (2in) trunk will have annual rings that are no more than 0.25mm(0.09in) wide!

In the centre of the trunk, the wood is darker and harder. This is the heartwood, which is dead, it neither stores sugars nor transports water. Heartwood is just structural timber, a prop to add physical strength to the trunk to enable it to support branches. This is why trees which become hollow can still thrive, though, naturally, a few do fall down.

The fine roots growing from the thicker ones absorb moisture and nutrients from the soil. Roots of intermediate size are unnecessary on a bonsai tree.

The paler wood is sapwood. This, too, is structural, but the outer rings are also involved in the transport of water and nutrients from the roots to the growing parts of the tree: the shoots, the leaves, flowers and fruit.

The rings which do the transporting are called the xylem (pronounced ‘zylem’). As xylem ages, it becomes less efficient until it ceases to have any function at all and becomes heartwood. In winter, the sugars are largely stored in vessels called medullary rays. These rays will radiate through the sapwood from the outer edge of the heartwood.

On the outside of the trunk are two darker, softer layers. The innermost layer is the phloem (pronounced ‘flo-em’), which distributes sugars from the leaves to the other parts of the tree, giving them energy to grow. If you ringbark a tree – cut a strip of bark away round the trunk – the tree will die. Not because the crown of the tree is starved of water, but because the roots don’t get the sugars they need to survive. When you damage the phloem by deep-pruning a branch or allowing training wire to crush the bark, it interrupts the flow of essential sugars. This may lead to the death of the roots below the damaged area. Each year a new layer of phloem is produced, but this doesn’t normally lead to the formation of such clearly visible rings as the xylem.

Enveloping the phloem is bark, which varies in thickness and texture according to species. Bark is made up of an accumulation of old, spent phloem, and has a variety of practical purposes. Bark is waterproof, so it prevents moisture from leaking out of the phloem. It is also home to small structures, called lenticels, which permit the trunk and the branches to ‘breathe’. Another function that bark performs is to protect the phloem from impact, abrasions and attack by a variety of insects or fungal infection.

These crowded pine candles have arisen in response to consistent pruning. They were generated by the activity of the cambium layer.