Fibres and sclereids

Sclerenchyma is a simple tissue, so all its cells are of one kind — but that one kind comes in two shapes, and the shapes do different work.

Figure to be added

Figure 1.9 — sclerenchyma in three views: a cross-section showing thick-walled cells packed with no gaps and only a small empty space at the centre of each; a longitudinal section showing the same cells as very long narrow fibres; and a separate group of sclereids, short and irregular in outline with extremely thick walls.

Fibres

Long and narrow cells, pointed at the ends, lying alongside one another in bundles. A bundle of fibres behaves like a rope — very strong when pulled along its length.

Sclereids

Short and irregular cells with extremely thick walls, scattered singly or in small groups. These behave like grit — hard, and resisting being crushed.

You have felt both, often

Bite into a pear and the faint grittiness is sclereids. Pull a thread from a coconut husk and that is a bundle of fibres. The two cell types are the same tissue solving two different problems: one resists being pulled apart, the other resists being crushed.

Why the shape follows from the job

A long thin cell has most of its lignified wall running in one direction, so it resists a pull along that direction. A short round cell has its wall thickened in every direction at once, so it resists pressure from anywhere. Neither shape is better — a plant needs both, in different places.