Wood is composed of:
The high strength of wood is derived primarily from its structure at the microscopic level. Wood is composed of long cells, in the axial direction, and thin cells in the radial and tangential directions.
The smallest microstructural component of wood is called a microfibril. Microfibrils are bundles of cellulose chains covered first by hemicellulose and then by lignin.
The long thin wood cells are composed of many layers of microfibrils. The microfibrils are arranged in separate differently oriented layers. The changing orientation of layers within the structure gives the wood cells better strength in more directions. The wood structure, however, is still considered to be very anisotropic.