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Stem of a Dicot Plant
Vascular Cylinder
This region comprises the pericycle, vascular bundles and pith (medulla).
* Pericycle
The pericycle is made up of sclerenchyma cells whichare lignified, dead fiber cells. These cells have thick, woody walls.
Functions of the Pericycle
* It strengthens the stem.
* It provides protection for the vascular bundles.
* VascularBundles
The vascular bundles are situated in a ring on the inside of the pericycle of the plant. This distinct ring of vascular bundles is a distinguishing characteristic of dicot stems. A mature vascularbundle consists of three main tissues - xylem, phloem and cambium. The phloem is located towards the outside of the bundle and the xylem towards the center. The cambium separates the xylem andphloem which bring about secondary thickening.
Functions of the Vascular Bundles
* The xylem provides a passage for water and dissolved ions from the root system to the leaves.
* The xylemalso strengthens and supports the stem.
* The phloem transports synthesized organic food from the leaves to other parts of the plant.
* The cambium, divides to produce new xylem andphloem cells, making secondary thickening possible.
* Pith (Medulla)
The pith occupies the large central part of the stem. It consists of thin-walled parenchyma cells with intercellular air spaces.Between each vascular bundle is a band of parenchyma, the medullar rays, with the cortex and the pith.
Functions of the Pith or Medulla
* The cells of the pith store water and starch.* They allow for the exchange of gases through the intercellular air spaces.
* The medullar rays transport substances from the xylem and phloem to the inner and outer parts of the stem.
Stemof a Monocot Plant
Epidermis
The epidermis consists of a single layer of living cells which are closely packed. The walls are thickened and covered with a thin waterproof layer called...