One last and very important component of the plant cell is its cell wall, something that animal cells lack entirely. The plant cell wall surrounds the membrane and is strong and rigid. Its purpose is to lend structural support to the cell and the tissue of which it is a part. Neighboring cells are held together by the outer, glue-like layers of their cell walls. Some specialized strengthening cells become mostly cell wall and do their job even after their death. The gritty grains in pear flesh, the fibers in celery stalks, the stone that surrounds a peach seed, and the seed coats of beans and peas are all mainly the cell-wall material of strengthening cells.