What is "vascular tissue"

Vascular \Vas"cu*lar\, a. [L. vasculum a small vessel, dim. of vas vessel: cf. F. vasculaire. See Vase, and cf. Vessel.]

1. (Biol.)

   1. Consisting of, or containing, vessels as an essential part of a structure; full of vessels; specifically (Bot.), pertaining to, or containing, special ducts, or tubes, for the circulation of sap.

   2. Operating by means of, or made up of an arrangement of, vessels; as, the vascular system in animals, including the arteries, veins, capillaries, lacteals, etc.

   3. Of or pertaining to the vessels of animal and vegetable bodies; as, the vascular functions.

2. (Bot.) Of or pertaining to the higher division of plants, that is, the ph[ae]nogamous plants, all of which are vascular, in distinction from the cryptogams, which to a large extent are cellular only.

   Vascular plants (Bot.), plants composed in part of vascular tissue, as all flowering plants and the higher cryptogamous plants, or those of the class Pteridophyta. Cf. Cellular plants, Cellular.

   Vascular system (Bot.), the body of associated ducts and woody fiber; the fibrovascular part of plants.

   Vascular tissue (Bot.), vegetable tissue composed partly of ducts, or sap tubes.

   Water vascular system (Zo["o]l.), a system of vessels in annelids, nemerteans, and many other invertebrates, containing a circulating fluid analogous to blood, but not of the same composition. In annelids the fluid which they contain is usually red, but in some it is green, in others yellow, or whitish.

n. 1 (context zoology anatomy English) The artery, veins, capillary, and associated tissues in an animal. 2 (context botany phytotomy English) The xylem, phloem, and associated tissues in a vascular plant.

n. tissue that conducts water and nutrients through the plant body in higher plants

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 Asteriidae dicots, 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 of the stem, woody plants also have a cork cambium that develops among the phloem. The cork cambium gives rise to thickened cork 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, 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 abaxial surface of the leaf. This is why aphids are typically found on the underside of the leaves rather than on the top, since the phloem transports sugars manufactured by the plant and they are closer to the lower surface.