Stems are sturdy structures that grow in order to give a plant a fighting chance to spread its leaves in the sun. Stem growth can add to the plant's height, broaden the area covered by the leaves, or even direct growth from a dark area toward one with more light. To provide mechanical support for a growing plant, stems need to be strong. To help move water and nutrients to the furthest reaches of the plant, stems are stuffed with little transport pipes in the form of xylem and phloem.