Sclerenchyma

Mature sclerenchyma cells are dead and have secondary cell walls thickened with cellulose and usually impregnated with lignin. In contrast to collenchyma, which is pliable, sclerenchyma is elastic. The cell cavity or lumen is very small or it may disappear completely. There are two types of sclerenchyma cells, namely sclereids and fibres.

1. Sclereids: The cells are irregular in shape. The cell walls are thick, hard and lignified which makes the lumen very small. Simple pits (canals) are found in the thickened cell walls and link adjacent cells. Sclereids are commonly found in fruit and seeds.
2. Fibres: The cells are needle-shaped with pointed tips, thick walls and rather small lumen. Secondary cell walls, impregnated with, are formed. Simple pits are also present. Fibres are abundant in the vascular tissue of angiosperms, i.e. flowering plants.

• sclerenchyma is an important supporting tissue in plants,
• sclereids are responsible for the hardness of date seeds and the shell of walnut,
• fibres probably play a role in the transport of water in the plant,
• starch granules are stored in the young, living fibres.