Pith, or medulla, is a tissue in the stems of vascular plants. It is composed of soft, spongy parenchyma cells that primarily function for storing and transporting nutrients throughout the plant. In eudicotyledons, pith is located in the center of the stem, while in monocotyledons, it extends into flowering stems and roots. The pith is encircled by a ring of xylem, which is in turn encircled by a ring of phloem. The cells in the peripheral parts of the pith may develop to be different from cells in the rest of the pith, and this layer of cells is then called the perimedullary region of the pithamus. The main function of the pith is to store and transport nutrients throughout the plant. In some plants, the pith in the middle of the stem may dry out and disintegrate, resulting in a hollow stem.