Companion cells are part of the phloem in plants. They are specialized parenchymal cells that are closely associated with sieve tube elements in the phloem. They are responsible for loading sugars and other organic compounds into the sieve tube elements for long-distance transport throughout the plant. The phloem is one of the two types of vascular tissue in plants, the other being xylem. Xylem is responsible for transporting water and minerals from the roots to the rest of the plant. The pericycle is a layer of cells in the roots that gives rise to lateral roots, while the pith is the central, often spongy, tissue of stems and roots.