Q...................... is a complex permanent tissue.

Complex permanent tissue is heterogeneous — made of several different cell types functioning together as one unit — and its job is always conduction, moving sap or food from a source region to a sink region. The two complex tissues in a plant are xylem and phloem.

Xylem is a dead tissue (hadrome) that conducts water and minerals and gives the plant mechanical rigidity. Its conducting cells are tracheids (present in all vascular plants, the sole conductors in pteridophytes and most gymnosperms, showing thickening patterns of increasing sophistication from annular through spiral, scalariform, reticulate to pitted) and vessels (formed by the fusion of a row of vessel elements after their end walls dissolve, the main conducting cells of angiosperms, wider and shorter-lived cell-by-cell than tracheids). Early-formed protoxylem (narrow, annular/spiral, able to stretch) matures toward the centre in stems (endarch) but toward the periphery in roots (exarch), while later-formed metaxylem (wider, reticulate/pitted) sits on the opposite side. Xylem parenchyma, the only living xylem cell type, stores food and moves sap laterally; xylem fibres add pure mechanical support. …