Xylem is responsible for conduction of water i.e., ascent of sap from roots to leaves. It was proved by Malpighi (1675) by girdling or ringing experiment.
Cambium is a layer, usually regarded as one or two cells thick, or persistently meristemaric tissue, giving rise to secondary tissues, resulting in growth in diameter.
Phloem is the food-conducting tissue, consisting of sieve tube, companion cells, parenchyma and fibers.