A rooted cutting from a side shoot of a tomato plant, Solanum lycopersicum (formerly Lycopersicon esculentum), from below. The picture shows the severed end of the cutting as it develops new roots (white), a week after being removed from the parent plant. The cut surface (centre, yellow hue ) has grown a protective callus tissue.The new roots appear as outgrowths from the stem just above the cut. This is because root formation is stimulated by the plant hormone auxin, indoleacetic acid (IAA), which is produced by the shoot tip and migrates downwards through the stem. In an intact plant, IAA regulates extension growth, but if the stem is cut, it accumulates above the cut surface, and stimulates the formation of new roots. Cuttings are used in horticulture to propagate a wide variety of plants. For the amateur grower, side-shoot cuttings are an inexpensive way of gaining new plants.