<P> In many vascular plants, secondary growth is the result of the activity of the two lateral meristems, the cork cambium and vascular cambium . Arising from lateral meristems, secondary growth increases the girth of the plant root or stem, rather than its length . As long as the lateral meristems continue to produce new cells, the stem or root will continue to grow in diameter . In woody plants, this process produces wood, and shapes the plant into a tree with a thickened trunk . </P> <P> Because this growth usually ruptures the epidermis of the stem or roots, plants with secondary growth usually also develop a cork cambium . The cork cambium gives rise to thickened cork cells to protect the surface of the plant and reduce water loss . If this is kept up over many years, this process may produce a layer of cork . In the case of the cork oak it will yield harvestable cork . </P> <P> Secondary growth also occurs in many nonwoody plants, e.g. tomato, potato tuber, carrot taproot and sweet potato tuberous root . A few long - lived leaves also have secondary growth . </P> <P> Abnormal secondary growth does not follow the pattern of a single vascular cambium producing xylem to the inside and phloem to the outside as in ancestral lignophytes . Some dicots have anomalous secondary growth, e.g. in Bougainvillea a series of cambia arise outside the oldest phloem . </P>

Describe how anomalous secondary growth takes place in amaranthus