Sclerenchyma - Sclereids

Sclerenchyma (Gk. scleros = hard) is where plant mechanical tissue goes once flexibility is no longer needed - its cells die at maturity, their protoplasm disappears, and what is left is a uniformly and heavily lignified secondary wall that is strong precisely because nothing living has to be accommodated inside it any more. Sclerenchyma comes in two forms, sclereids and fibres; this section covers the sclereids (stone cells) - typically isodiametric, though some are elongated, with a wall so thick from lignification that the internal lumen shrinks almost to nothing, connected to neighbouring cells only through simple or branched pits. Their job is purely mechanical/protective: they are what gives seed coats, endosperms and certain fruit flesh (pear, guava, strawberry) their characteristic hard or gritty texture. Five (sometimes six) shapes are recognised, essentially by silhouette: brachysclereids or stone cells, roughly isodiametric, found in bark, pith, cortex, hard endosperm and fleshy fruit pulp; macrosclereids, elongated rods found lining a legume seed coat; osteosclereids or bone cells, rod-shaped but with characteristically dilated (swollen) ends, in leaves and seed coats; astrosclereids or star cells, with several arms radiating from a central body, in petioles and leaves; trichosclerei …