Bark
The outside layer of the trunk. The bark serves as a protective layer for the more delicate inside wood of the tree.
Cambium
The thin layer of living cells just inside the bark. This part of the tree makes new cells allowing the tree to grow wider.
Sapwood
A network of living cells that bring water and nutrients up from the roots. When the inner layers of sapwood die they become heartwood.
Heartwood
Heartwood is dead sapwood in the centre of the trunk – giving the tree support and strength. It is usually darker in colour than the sapwood and is the hardest wood of the tree.
Pith
The tiny dark spot of spongy living cells is the centre of the tree which carries nutrients up to the rest of the tree – it is also called the heart of the tree. It is the most important, which is why is the most protected.