First 136 words of the document:
The structure of wood:
The structure of wood is a large number of fibres (short pipes)
glued together by a substance called lignin all in a parallel
direction. The fibres are hollow and their walls consist of
compounds called cellulose and hemicelluloses (chemicals
related to sugar).
In hardwoods the fibres are about 1mm long, in softwoods the
fibres are 3-8mm long.
The trunk of the tree consists of heartwood- in the middle, and
sapwood closer to the surface. The cells living in the sapwood
are living; they carry and store nutrients for the tree. Whereas
the heart wood is dead, however the wood, depending on the species may contain heartwood
pipes with colour extracts, and may make it more rot resistant.