A permanent tissue whose cells have different size, shape and structural characteristics is called complex tissue. Complex tissue is divided into two parts. Xylem and phloem.
1. Zylem: Greek word Xylon means wood. The tissue that transports water and mineral salts from the root of the plant to different parts of the body is called xylem. It consists of four components. Trachyds, trachea or vessels, xylem fibers and xylem parenchyma. Among them xylem parenchyma is the only living material. Xylem fibers are called wood fibers. Coconut fiber or coir is a type of wood fiber. Ferns and gymnosperms do not have vessels. Besides, the plants of Winteraceae, Tetracentraceae, Trochodendraceae etc. do not have vessels. Different types of xylem are-
(i) Protoxylem: Vessel cells with narrow pores are called protoxylem.
(ii) Metaxylem: Vessel cells with large pores are called metaxylem.
(iii) Exarc: If protoxylem is towards the periphery and metaxylem towards the centre, it is called exarc. Root xylem is exarc in nature.
(iv) Endarc: If protoxylem is towards the center and metaxylem towards the periphery, it is called endarc. The xylem of stem is endarc in nature.
(v) Mesarc : When protoxylem and metaxylem are arranged on both sides, it is called mesarc. Mesarc xylem is found in the leaves of ferns and cycads.
(vi) Centrach : When protoxylem is in the center and metaxylem is located around it, it is called centrach. Centarch xylem is found in fern plants.
Functions of Xylem
(i) Transports water and mineral salts in the plant body.
(ii) Stores water and mineral salts in the plant body.
(iii) It imparts vigor to plants.
(iv) Provides mechanical energy to plants.
(v) Assists in photosynthesis of plants.
(vi) Helps plants in respiration.
(vii) Aids diffusion and osmosis in the plant body.
(viii) It forms wood in the plant body.
(ix) It participates in the formation of the main structure of the plant body.
2. Phloem : Greek word Phloos mean bark. It transports food from plant leaves to different parts of the body. It consists of four components. Synovial, companion cells, phloem parenchyma and phloem fibers. The resulting sivnol or sivcell does not have a nucleus. The fibers present in the secondary phloem are called bast fibers. Jute fibers are bast fibers.
Functions of Phloem
(i) Phloem transports food in the plant body.
(ii) Stores food in the plant body.
(iii) Assists in photosynthesis of plants.
(iv) It imparts vigor to plants.
(v) Provides mechanical energy to plants.
(vi) It forms fibers in the plant body.