Sclereids are a type of plant cell known for their hard, woody structure. They provide support and protection to various parts of plants, such as seeds and fruits. Sclereids can vary in shape and size, often appearing as irregularly shaped cells that contribute to the toughness of certain plant tissues. These cells are commonly found in pears and walnuts, where they contribute to the gritty texture of the fruit and the hardness of the shell, respectively. Sclereids are part of a larger group of cells called sclerenchyma, which also includes fibers that help strengthen plant structures.