Selasa, 09 Oktober 2012

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Structure And Fuction Of Vascular Tissue


Vascular Tissue 

Vascular tissue consist of xylem and phloem.
The xylem of stem

The phloem of stem

Xylem is vascular tissue that is responsible for the conduction of water and mineral salt from soil (root) to leaves. Xylem consist of death cells and living cells whose walls are impregnated with lignin. The cells are in lines and form vascular bundle.

During the development process, xylem is distinguished into primary xylem and secondary xylem. Primary xylem is derived from the growth and differentiation of meristematic tissue (procambium) at stem tit. Whereas secondary xylem is derived from cambium growth.

Xylem consist of four types of cell, namely trachea or vessel element, tracheid, xylem fiber, and parenchyma.

Phloem is a vascular tissue which function in conduction of nutrition from leaves throughout the plant. Phloem can be found in bark and is composed of living cells. Those cells will disappear reaching maturity.
Phloem is composed of four types of cells.

  1. Sieve tube. It has cylindrical shape with a number of pores at the end of the wall which makes the connection of intracellular cytoplasmic possible. 
  2. Companion cell. It has cylindrical shape and contains thick plasma.
  3. Pholem fiber. It has thick wall and long shape which becomes gradually narrower towards one end.
  4. Phloem parenchyma. The cells have primary walls with small pores (pit).

Vascular Cambium 
Maristematic tissue is present in between primary xylem and phloem. In most stems, meristematic area develops into vascular cambium.

Pith and Pith Rays
Pith is composed of large-called parenchyma with numerous intracellular spaces. Its principal function is as the storage of food.

In some stream, primary vascular bundles are separated by wide stripes of parenchyma that extend from the pith to the cortex. Such stripes of parenchyma are called pith rays. Part of plant in which there are primary vascular tissues, pith, and rays is called stele (vascular cylinder)

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