Strengthening tissue composed of relatively short cells (sclereids
) and/or relatively long ones (fibres
) with thick, often lignified, cell walls and usually lacking a living protoplast at maturity. Sclerenchyma cells usually possess simple unbordered pits, although *fibre-tracheids
may have pits with a slightly raised border. Sclerenchyma may form by thickening (sclerification) of the secondary walls of parenchyma cells, often involving lignification, or it may develop directly from meristematic tissue.