Young or newly sprouting roots are covered in a permeable outer layer and are typically responsible for a tree's uptake of nutrients from the soil. Many newly developed roots produce tiny cellular projections, often referred to as root hairs, which extend between soil particles to absorb water and minerals. Although these tiny hairs are usually less than one third of an inch long, their great numbers enormously increase the surface area from which the tree can collect water. Young or new roots are formed by a zone of cells termed meristems that posses the embryonic-like capability to actively divide and produce specialized types of cells as needed. In forming new roots, this tissue must produce two different types of cells. One type of cell grows in an outward direction from the plant and develops into cap that covers the tip of the root. This root cap is designed to protect tender new root tissues as it probes and explores the soil and will eventually slough off from the main root body. Most of the meristemic cells however divide to produce a region of new root tissue. This region is located behind the protective root cap and meristemic tissue and expands toward the direction of the plant to fuse new root with old root tissue. Although young roots are delicate and slender, the forward thrust of the root tip and the expanding cells can exert sufficient pressure to split rock.