Anatomy of root

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1. Anatomy of Root By Dr. Gunmala Gugalia Associate Professor Dept. of Botany, Sangam University Bhilwara , Rajasthan(India)

2. six anatomical characteristics of the root. The characteristics are: 1. Root Cap  2. Epidermis  3. Cortex  4. Endodermis  5.  Pericycle   6. Vascular System.

3. Root: Anatomical Characteristic # 1 . Root Cap: The root cap consists of parenchymatous cells in various stages of differentiation. It is protective in function.  The root cap is apparently the site of the perception of gravity ; thus it appears to be capable of controlling the production in the meristem of the growth- regulating substances involved in geotropism or their movement. 2 .  Epidermis: T he epidermis is also known as epiblema or piliferous layer. In most of roots, root hairs develop from some of the epidermal cells at a little distance from the apical meristem

4. 3. Cortex: In most roots the cortex is parenchymatous . In some roots, the cells of the cortex are very regularly arranged, both radially and in concentric circles. Conspicuous intercellular spaces may be present, and especially evident in aquatic species, where they form a type of aerenchyma . The cortical cells often contain starch, and sometimes crystals. Sclerenchyma is more common in the roots of monocotyledons than those of dicotyledons . The innermost layer of the cortex is usually differentiated as an endodermis.

5. 4. Endodermis : The endodermis comprises a single layer of cells differing physiologically and in structure and function from those on either side of it . In the young endodermal cells a band of suberin , Casparian strip, runs radially around the cell and is thus seen in the radial walls in transverse sections of roots . The thin-walled passage cells often remain in the endodermis in positions opposite the protoxylem which is known as passage cells

6. Casperian strips in Endodermis

7. 5.  Pericycle : The pericycle is usually a single layer of parenchymatous cells lying just within the endodermis and peripheral to the vascular tissues. The pericycle has a capacity for meristematic growth, and gives rise to lateral root primordia , parts of the vascular cambium, and usually the meristem which produces cork, the phellogen . The pericycle is sometimes called pericambium .

8. 6. Vascular System: The vascular system of the root as seen in transverse section consists of a variable number of triangular rays of thick-walled, lignified tracheary elements, alternating with arcs of thin-walled phloem . In the root, the xylem and phloem do not lie on the same radius. The xylem may form a solid central core, or there may be a parenchymatous or sclerenchymatous pith, as in the roots of many monocotyledons . Roots with 1, 2, 3, 4, 5 and many arcs of xylem are respectively called monarch, diarch , triarch , tetrarch, pentarch and polyarch . The xylem is exarch , i.e., protoxylem lies towards periphery and metaxylem towards the centre.

9. The xylem is always centripetal in its development. The phloem bundle consists of sieve tubes, companion cells and phloem parenchyma. The protoxylem consists of annular and spiral vessels and meta-xylem of reticulate and pitted vessels. The parenchyma found in between xylem and phloem bundles is known as conjunctive tissue . The pith may be large, small or altogether absent.

10. Anatomy of Root Dicot root Monocot root

11. Difference between dicot and monocot root 1. Cortex is comparatively narrow. 2. The epiblema , the cortex and even the endodermis are peeled off and replaced by cork. 3. Older root has a covering of cork. 4. Endodermis is less thickened and casparian strips are more prominent. 5. Passage cells are generally absent in endodermis. 6. Pericycle produces lateral roots, cork cambium and part of the vascular cambium. 1. Cortex is very wide. 2. Cork is not formed. The cortex and the endodermis persist. Only the epiblema is peeled off. 3 . Older root has a covering of exodermis . 4. Casparian strips are visible only in young root. The endodermal cells later become highly thickened. 5. Thin walled passage cells generally occur in the endodermis opposite the protoxylem point. 6. Pericycle produces lateral roots only. Dicot Root Monocot root

12. Difference between dicot and monocot root 7. The number of xylem and phloem bundles varies from 2-5 or sometimes 8. 8. Xylem vessels are generally angular. 9. Conjunctive tissue is parenchymatous . 10. Conjunctive parenchyma forms the cambium. 11. Secondary growth takes place with the help of vascular cambium and cork cambium. 12. Pith is either absent or very small. 7. Xylem and phloem bundles are numerous and are 8 or more in number. 8. Xylem vessels are oval or rounded. 9. Conjunctive tissue may be parenchymatous or sclerenchymatous . 7. Conjunctive parenchyma does not produce cambium. 10. Secondary growth is absent. 11. A well-developed pith is present in the center of the root. Dicot Root Monocot root