greatly elongated wood cells with narrowed ends that make for wood’s durability and hardness.
The walls of libriform cells are lignified, with occasional oblique pores. In hardwoods (oak, ash), the walls are greatly thickened; this is less true in softwoods (linden, poplar). In some species (maple, elder), the cell walls are thin, holding live protoplast for long periods and containing nutrients (fats, starches). Sometimes, in their early stages of formation, libriform cells are divided by thin transverse septa that retain their living contents and nutrients for long periods (septal libriform). Libriform fibers developed evolutionarily from tracheids during the process of specialization of wood cells.