Cross section through a Helianthus stem showing a vascular bundle. Contained in this is the phloem (small red circles), xylem (larger red circles) & cambium between the two. Phloem is made up of sieve elements placed end to end so as to form a sieve tube; this is responsible for the translocation of organic substances. Xylem is made up of nonliving vessels (large hollow tubes made from lignified cells placed end to end) & smaller traechids (elongated lignified cells). This tissue is chiefly responsible for the transport of water & minerals from the roots to the leaves. It also contributes to the strength of the stem, along with the collenchyma and sclerenchyma.