What is the difference between Primary Vascular Tissue and Secondary Vascular Tissue?

Vascular tissue can be primary (growing from the apical meristem and elongating the plant body) or secondary (growing from the cambium and increasing stem girth).

Primary vascular tissue (primary xylem and phloem derived from the apical meristem) is made as the tracheophyte (vascular plant) grows taller. Secondary vascular tissue is derived from the cambium as the plant grows wider.

Secondary growth is an evolutionary advance that allows plants to grow taller because the can form very thick stems (woody trunks).

Seedless plants and nearly all monocotyledons and herbaceous eudicotyledons, have only primary vascular tissue. The evolution of vascular tissue, especially xylem with its rigid water-conducting cells known as tracheids, provided the plant stem with greater support and allowed plants to grow upright to great heights

Secondary vascular tissue is vascular tissue (xylem and phloem) formed by the vascular cambium during secondary growth in a vascular plant. Secondary growth is growth characterized by an increase in thickness of stem and root

Primary tissues: Tissues generated from the growth of an apical meristem.

Secondary tissues: Tissues generated from the growth of a cambium.

vascular tissue - conduction
 *xylem - water and dissolved materials
 *phloem - carbohydrates

Xylem
? principle water-conducting tissue
 *combination of vessels and tracheids
? primary xylem derived from procambium
? secondary xylem formed by vascular cambium
 *wood made of accumulated secondary xylem

Phloem
? principle food-conducting tissue in vascular plants, located toward the outer part of roots and stems
*carried out through sieve cells and sieve-tube members
*some sieve areas (pores) have larger pores called sieve plates
*each sieve-tube member associated with companion cell

In monocots, primary xylem is in discrete vascular bundles arranged in a ring surrounding pith.
? primary phloem differentiated in discrete groups of cells between the arms of the xylem in both monocots and dicots.

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