4.5—Sclerenchyma, xylem and phloem

Xylem vessels conduct water and mineral ions and support the stem; phloem translocates dissolved organic solutes; sclerenchyma fibres provide support without being a transport pathway.

Mature xylem vessels are dead, hollow and lignified, with pits for lateral water movement. Phloem contains living sieve-tube elements and companion cells, carries sap from sources to sinks in either direction, and lacks xylem’s lignified transport tube. Sclerenchyma fibres are dead, thick-walled support cells with end walls.

In a stem cross-section, xylem is toward the centre and phloem toward the outside, often associated with sclerenchyma. The position plus tissue structure helps identify function.

Phloem transport is not restricted to “upwards”, and sieve tubes are not simply miniature xylem vessels. Keep support, water transport and organic-solute translocation distinct.