A rooted cutting from a side shoot of a tomato plant, Solanum lycopersicum (formerly Lycopersicon esculentum). The picture shows the base of the cutting as it develops new roots (white), one week after being removed from the parent plant.The new roots appear as outgrowths from the stem. Root formation is stimulated by the plant hormone auxin, indoleacetic acid (IAA), which is produced by the shoot tip (here, beyond the top of the picture) and migrates through the stem. In an intact plant, IAA regulates extension growth, but if the stem is cut, it accumulates at the cut surface, and stimulates the formation of new roots in the region above. The roots just below centre are about 3mm long.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.