Selasa, 18 September 2012

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Structure And function Of Plant Tissue Cortex

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Cortex

Cortex Tissues : 
a. Parenchyma
b. Collenchyma
c. Sclerenchyma

Cortex is a complex tissue derived from ground meristem development. It is formed beneath the epidermis as a cylindrical zone that extends inward to be primary phloem. The following tissues can be found in the cortex.

Parenchyma
Parenchyma is a part of primary ground meristem system. It consist of large cell with thin walls. The tissue composition is loosely packed with intercellular air spaces and large vacuoles.

Parenchyma is present in epidermis and pith, and between xylem and phloem. There are several types of parenchyma as follows.

  1. Aerenchyma, which is parenchyma tissues containing large air spaces. For example, parenchyma cell on aquatic plant stem.
  2. Chlorenchyma, which is parenchyma tissue containing chloroplast. It fuction in photosysthesis.
  3. It function in photosynthesis.
  4. Parenchyma tissues have several functions as follows.
  5. As the bulk of ground tissues or places for other tissues.
  6. Photosistesis.
  7. Food storage, e.g on peanut (Phaseolus sp.) or sweet potato (Impomoea batatas).
  8. Wound healing.


Collenchyma
Collenchyma is resulted from parenchyma differentiation and serves as a supporting and strengthening tissue of plant organ. It consist of thick-walled cell whose corners experience thickening of cellulose and pectin. The unevenly cell wall thickening form angular collenchymas and lamellar collenchya.

Sclerenchyma
Sclerenchyma tissues function as organ support. The tissues consist of inactive cells and have thick-walled cells. It has compact cell composition, so that they have no intracellular air space. The wall cells contains cellulose and lignin.

Sclerenchyma tissues can be distinguished into two types, sclereids and fibers.


  1. Scelereids : Scelereid is hard and rigid. It is found in the stem cortex, leaf, venation, root, fruit, and seed.
  2. Fiber : Fiber is composed of hard elongated cells with pointed ends, and it function in support and protection. Fiber cells can be found in gymnosperm woody fiber, bark, leaf fiber, and seed fiber.


Secretory Tissue
Secretorry tissue are parenchyma-like and contain dense protoplasm. They secrete various substances, such as resinous material and nectar.

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