Pear fruit (Pyrus sp.) sclerenchyma cell, coloured scanning electron micrograph (SEM). Shown here is a section through a pear fruit revealing a sclereid, also known as a stone cell. Sclereids (sclerenchyma cells) are cells composed of thick cell walls that surround a very small cell cavity. The thick cell walls consist of cellulose, hemicellulose and lignin and often show distinct layering. The small holes within the cell wall layers are called plasmodesmata. Plasmodesmata are microscopic channels, in plants, traversing the cell walls of plant cells and enabling transport and communication between them. Although cell walls are permeable to small soluble proteins and other solutes, plasmodesmata enable direct, regulated, intercellular transport of substances between cells. Mature sclerenchyma is composed of dead cells with extremely thick cell walls (secondary walls) that make up to 90% of the whole cell volume. Magnification: x160 when shortest axis.
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