Part – 3: Anatomy of Normal and Coralloid Root
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Cycas Anatomy of Tap-Root
Ø The primary anatomical structure of Cycas tap-root resemble that of dicot root
Ø The T.S. is circular in outline.
Ø Anatomically the tap-root is differentiated into FOUR regions.
(1). Epiblema (Epidermis)
Ø The outermost layer,
Ø Cells are parenchymatous and single-layered
Ø Contain plenty of root hairs for the absorption of water and minerals
(2). Cortex
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Ø Cortex is located inner to the epidermis.
Ø Composed of multilayered parenchymatous cells.
Ø Cortical cells are loosely arranged with plenty of intercellular spaces.
Ø Cell contain plenty of starch grains as deposition
Ø Few tannins cells are also present in the cortex.
(3). Endodermis and Pericycle
Ø Endodermis is single-layered and inconspicuous.
Ø Pericycle usually multilayered.
(4). Central stele
Ø The stele is located inner to pericycle in the centre.
Ø Vascular bundles radial and diarch
Ø Diarch: Two xylem and phloem strands alternatively arranged.
Ø Xylem is exarch (protoxylem directed towards the exterior)
Ø Secondary thickening occurs in the tap-root.
Ø Secondary thickening is similar to the dicot roots
Ø A continuous ring of cambium is differentiated it cuts secondary xylem towards the inner side and secondary phloem towards the outer side.
Ø Periderm formation also occurs in mature tap-root as usual.
Learn more: Difference between Coralloid Root and Tap-Root in Cycas
Anatomy of Coralloid Roots
Ø Coralloid roots are a special type of negatively geotropic, highly branched and symbiotic root found in Cycas. (See Morphology of Cycas for details.)
Ø The anatomy of the coralloid root is more or less similar to the normal root (tap-root)
Ø Anatomically it is differentiated into:
(1). Epiblema
(2). Cortex
(3). Vascular Tissue
(1). Epiblema (Epidermis)
Ø The outermost layer
Ø Cells are parenchymatous and single-layered
Ø Root hairs are ABSENT in the epidermis
(2). Cortex
Ø Cortex is located inner to the epidermis.
Ø Cortex is large and differentiated into THREE zones
(a). Outer Corte
(b). Middle Cortex
(c). Inner Cortex
Ø Cells of the cortex are parenchymatous and loosely packed with plenty of inter-cellular spaces.
Ø The middle zone of the cortex is called ALGAL Zone.
Ø In the algal zone, the cortical cells (single layer) are radially elongated.
Ø Blue-green algae (Anabaena cycadae) occur endophytically in the middle layer of the cortex.
Cycas Coralloid Root Diagram
Ø These algae in the algal zone are symbiotic.
Ø They help in nitrogen fixation.
Ø The endodermis is single-layered and it separate stele from the cortex.
Ø Pericycle multilayered and prominent.
(3). Vascular Tissue
Ø Vascular tissue is located in the central region of the root
Ø Vascular bundles are Radial and Triach
Ø Triarch: Three traces of xylem and phloem arranged alternatively
Ø The xylem exarch (protoxylem is located towards the periphery)
Ø Pith is usually absent, very small if present.
Ø Secondary thickening usually absent in coralloid roots.
Learn more: Difference between Coralloid Root and Tap-Root in Cycas
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