Vascular tissue is a complex conducting
tissue, formed of more than one cell type, found in
vascular plants. The primary components of vascular tissue are the
xylem and
phloem. These two tissues transport fluid and nutrients internally. There are also two
meristems associated with vascular tissue: the
vascular cambium and the
cork cambium. All the vascular tissues within a particular plant together constitute the vascular tissue system of that plant.
The cells in vascular tissue are typically long and slender. Since the xylem and phloem function in the conduction of water, minerals, and nutrients throughout the plant, it is not surprising that their form should be similar to pipes. The individual cells of phloem are connected end-to-end, just as the sections of a pipe might be. As the plant grows, new vascular tissue
differentiates in the growing tips of the plant. The new tissue is aligned with existing vascular tissue, maintaining its connection throughout the plant.
The vascular tissue in plants is arranged in long, discrete strands called
vascular bundles. These bundles include both xylem and phloem, as well as supporting and protective cells. In
stems and
roots, the xylem typically lies closer to the interior of the stem with phloem towards the exterior of the stem. In the stems of some Asterales
dicot
The dicotyledons, also known as dicots (or, more rarely, dicotyls), are one of the two groups into which all the flowering plants (angiosperms) were formerly divided. The name refers to one of the typical characteristics of the group: namely, t ...
s, there may be phloem located inwardly from the xylem as well.
Between the xylem and phloem is a
meristem called the vascular cambium. This tissue divides off
cells that will become additional xylem and phloem. This growth increases the girth of the plant, rather than its length. As long as the vascular cambium continues to produce new cells, the plant will continue to grow more stout. In
trees and other plants that develop
wood, the vascular cambium allows the expansion of vascular tissue that produces woody growth. Because this growth ruptures the
epidermis
The epidermis is the outermost of the three layers that comprise the skin, the inner layers being the dermis and hypodermis. The epidermis layer provides a barrier to infection from environmental pathogens and regulates the amount of water rele ...
of the stem,
woody plants also have a
cork cambium that develops among the phloem. The cork cambium gives rise to thickened
cork
Cork or CORK may refer to:
Materials
* Cork (material), an impermeable buoyant plant product
** Cork (plug), a cylindrical or conical object used to seal a container
***Wine cork
Places Ireland
* Cork (city)
** Metropolitan Cork, also known as G ...
cells to protect the surface of the plant and reduce water loss. Both the production of wood and the production of cork are forms of
secondary growth.
In
leaves
A leaf (plural, : leaves) is any of the principal appendages of a vascular plant plant stem, stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", wh ...
, the vascular bundles are located among the spongy
mesophyll. The xylem is oriented toward the
adaxial surface of the leaf (usually the upper side), and phloem is oriented toward the