Root systems consist of a main or primary root, rootlets or secondary roots, and root hairs. The primary root arises from the embryo. The primary root system of many plants is short-lived and is replaced by a secondary root system. These secondary root systems become the permanent roots of many monocotyledons such as the grasses.
Root hairs are specialized cell extensions which penetrate into the openings between soil particles.
The outside wall of the cell becomes distended to form a tubular outgrowth which makes contact with the soil and absorbs water and dissolved minerals from it. Water and soluble nutrients enter the root hairs, pass into the rootlets, and travel through the main root into the stems and leaves. Root hairs are formed in great numbers near the tips of roots. In most plants they are short-lived. If a plant is transplanted carelessly, it is the loss of many of these small root hairs with their water-absorbing cells that will cause the plant to wilt.