Vascular tissue is an adaptation to multicellularity and life on land. Xylem transports water and dissolved minerals from roots upwards. Xylem cells are elongated with thick walls and are dead. Phloem transports dissolved carbohydrates throughout a plant and includes sieve cells and the more specialized sieve tube members. Pores of sieve tube member cells cluster at sieve plates, allowing more efficient nutrient transport.
Companion cells help transfer carbohydrates.
A stem is the central axis of the shoot and consists of nodes, where leaves attach, and internodes between leaves, where the stem elongates. Vascular bundles in the stem contain xylem and phloem, which are scattered in monocots and form a ring in dicots. Between a stem's epidermis and vascular tissue lies the cortex, made of ground tissue. Pith is storage ground tissue in the center of a stem. Stem modifications include stolons, thorns, succulent stems, tendrils, and tubers.