Softwoods are derived from gymnosperms; hardwoods from angiosperms.
Both contain longitudinal tracheids, but hardwoods also contain fibres
and vessels. Both woods have storage parenchyma, but in hardwoods, this
is usually more extensive. Rays are present in both woods, but
hardwoods often have multiseriate rays. The rings of softwoods and
hardwoods are caused by seasonal changes in xylem tube diameter, but in
diffuse porous hardwoods this is less marked.
Tensile strength is a result of the multi-fibre nature of wood: it
is made of fibres (cells), themselves made of spun fibres (cellulose).
Compressive strength is mostly a result of the macromolecular matrix
provided by lignin in the cell wall, which crosslinks the fibres.