Two types of sclerenchyma cells exist&colon; fibers and sclereids. The pulvinus is a motor structure consisting of a rod of sclerenchyma surrounded by collenchyma. The term "sclerenchyma" (originally "Sclerenchyma") was introduced by Mettenius in 1865. These tissues are mainly of two types&colon; sclerenchyma fiber and sclereids. Sclereids are the reduced form of sclerenchyma cells with highly thickened, lignified walls. Sclerenchyma and vascular cells do not fold, providing support for the plant. Sclerenchyma is the supporting tissue in plants. Sclerenchyma cells have a narrow lumen and are long, narrow and unicellular. Sclerenchyma cells are the principal supporting cells in plant tissues that have ceased elongation. The adaxial sclerenchyma tissue sometimes forms strands that are opposite or extend to epidermal veins. Sclerenchyma is the tissue which makes the plant hard and stiff. Sclerenchyma is Greek word where "Sclero-" means hard and "enchyma" means infusion.