Final answer:
Sclerenchyma is the specialized plant cell type containing two cell types, fibers and sclereids, both having secondary cell walls thickened with lignin.
Step-by-step explanation:
The specialized plant cell type that contains two types of cells, fibers and sclereids, is the sclerenchyma. These cells are characterized by secondary cell walls that are thickened with deposits of lignin, which is a key component in wood. Sclerenchyma fibers are used by humans to make products such as linen and rope. The two types of sclerenchyma cells differ in size and shape: fibers are long and slender, whereas sclereids are smaller and can give pears their gritty texture.