Sclerenchyma - Fibres

The second sclerenchyma type, fibres, are the most elongated dead cells the plant makes - very long, tapering to a point at both ends, with lignified walls, a narrow lumen and only simple pits, since (unlike a tracheid) a fibre's job is pure mechanical strength, not conduction. That single-mindedness of purpose is also what makes fibres so economically valuable: cottage and textile industries depend on them directly. The book groups fibres two ways. By where they sit relative to the xylem, wood/xylary fibres (derived from vascular cambium, associated with secondary xylem, itself split into libriform fibres, fibre-tracheids, septate fibres and gelatinous fibres) are distinguished from bast/extra-xylary fibres (present in the phloem or outer bark - jute, kenaf, flax, hemp - historically mislabelled 'pericyclic' fibres even though they are really phloem fibres), and from surface fibres (from the seed testa, e.g. cotton), mesocarp fibres (from the fleshy middle fruit layer, e.g. coconut) and leaf fibres (e.g. Musa, Agave). By economic use, fibres are grouped into textile fibres (further split into surface fibres like cotton, soft fibres like flax/jute/ramie, and hard fibres like sisal/coconut/pineapple), brush fibres, rough-weav …