146 Tracheids.p65

Tracheids, vessels and sieve tubes are found in the vascular tissue of the plant. • Tracheids and vessels are found in the xylem tissue and conduct water and dissolved mineral ions from the roots to the aerial parts of the plant. • Sieve tubes are found in the phloem tissue and conduct organic solutes, for example, sugars and amino acids, up and down the plant, from where they are synthesised to where they are required. Xylem and phloem are characteristic of the higher plants called Tracheophytes, which include ferns, conifers and flowering plants. Lower plants such as liverworts and mosses do not develop xylem or phloem. The special water conducting cell known as the tracheid is characteristic of the xylem tissue in ferns and conifers. In flowering plants, although some tracheids may be present, a more specialised system of water conducting xylem vessels has evolved.