noun, plural: sclereids
A type of sclerenchyma cell of varying shapes but are typically shorter than sclerenchyma fibers, and whose function is to provide strength and support
A sclerenchyma is a plant cell type that is distinct from other fundamental plant cell types such as parenchyma and collenchyma. It is characterized by having a thick and lignified cell wall due to a secondary wall thickening. The sclerenchyma cell deposits a secondary cell wall between the primary cell wall and the plasma membrane. The cell also loses its protoplast at maturity. Thus, its primary function is to provide strength or support to soft tissues, such as ground tissues. It is also present in the vascular tissues, xylem and phloem. There are two types of sclerenchyma cells: the fiber cell and the stone cells or sclereids.
Sclereids are sclerenchyma cells that are different from fibers in a way that they vary in shape. Fibers are elongated cells. Sclereids are usually isodiametric (i.e. roughly spherical or polyhedral). They may be branched. They may occur singly (an idioblast) or in small groups. They are usually shorter than fibers. They give rise to the gritty texture in, for instance, the pear fruit. They may also occur in layers, for example in hard seed coats. In phloem tissues, there are more sclereids in secondary phloem than in the primary phloem.