In this article we will discuss about the anatomy of different dicot roots: 1. Ranunculus – Root 2. Cicer – Root 3. Tinospora – Root 4. Ficus – Root.
1. Anatomy of Ranunculus – Root (Family – Ranunculaceae):
It is circular in outline and reveals the following tissues from outside with-in:
Epiblema:
1. Outermost, single – layered epiblema consists of barrel shaped or rectangular cells.
2. From some cells arise unicellular hairs.
Exodermis:
3. Few layered exodermis is present below epiblema. The cells are thin walled and without any intercellular spaces.
Cortex:
4. Many layered cortex consists of thin walled, rounded, oval or polygonal cells.
5. It is parenchymatous, with many intercellular spaces. The cells are filled with starch grains.
6. Endodermis is the innermost cortical layer consisting of barrel shaped cells.
7. The endodermal cells are thick-walled and contain casparian strips. A few thin walled passage cells are also present against the protoxylem.
Pericycle:
8. Single layered pericycle consists of thin walled, small cells, and lies immediately inner to the endodermis.
Vascular Bundles:
9. These are radial and exarch.
10. Four xylem strands alternate with the four phloem strands showing tetrarch condition.
11. Protoxylem lies towards the periphery (i.e., exarch), and consists of annular and spiral vessels.
12. Metaxylem vessels meet in the centre and consist of pitted and reticulate vessels.
13. Four patches of phloem consist of sieve tubes, companion cells and phloem parenchyma.
Pith:
14. It is absent.
Identification:
(a) 1. Presence of vessels in the xylem.
2. Vessels have perforated end walls with scalariform and regularly arranged holes. (Angiosperms)
(b) 1. Presence of unicellular root hairs.
2. Radial vascular bundles.
3. The xylem is exarch. (Root)
(c) 1. Presence of tetrarch condition.
2. Pith is absent. (Dicotyledones)
2. Anatomy of Cicer – Root:
It is circular in outline and reveals following tissues from out side with-in:
Epiblema:
1. It is the outermost layer consisting of many thin walled cells.
2. From some of its cells arise unicellular hairs.
3. Cuticle is absent.
Cortex:
4. It is very large, parenchymatous and well developed occupying the big part of the section.
5. In this region there are present many intercellular spaces.
6. Cortical cells are filled with starch grains.
7. In older sections, few layered exodermis, consisting of thin walled compact cells, is present just below the epiblema.
8. Endodermis is the ring like innermost layer of cortex made up of barrel shaped cells.
9. Casparian strips are present in the endodermal cells.
10. Some of the endodermal cells, particularly opposite to the protoxylem, are thin walled and have been termed as passage cells.
Pericycle:
11. Single – layered, ring like pericycle is present close to the endodermis on its inner side.
12. It is also a compact layer of thin walled cell.
Vascular Bundles:
13. The vascular bundles are 2 to 6 and radial, i.e., xylem and phloem on different radii alternating with each other.
14. Xylem and phloem patches are equal in number.
15. Xylem consists of protoxylem and metaxylem.
16. Protoxylem is exarch and consists of small annular and spiral vessels.
17. Metaxylem strands are big, present towards the centre and composed of large reticulate and pitted vessels.
18. In some cases the metaxylem meet in the centre and thus obliterating the pith.
19. Phloem composed of sieve tubes, companion cells and phloem parenchyma.
20. In mature roots,.cambium also appears cutting the secondary structures.
21. The parenchymatous cells in between xylem and phloem strands form conjunctive tissue.
Pith:
22. It is very small, parenchymatous and without any intercellular spaces. It gets reduced after the formation of secondary structures.
Identification:
(a) 1. Presence of vessels in the xylem.
2. Vessels have perforated end walls with scalariform and regularly arranged holes. (Angiosperms)
(b) 1. Presence of unicellular root hairs.
2. Vascular bundles are radial and xylem is exarch. (Root)
(c) 1. Vascular bundles are 2-6.
2. Reduced pith. (Dicotyledones)
3. Anatomy of Tinospora – Root:
T. S. appears circular in outline and reveals following tissues from outside with-in:
Periderm:
1. It consists of cork, cork cambium and secondary cortex which are also termed as phellem, phellogen and phelloderm, respectively.
2. Cork is the outermost region of the section, consisting of dead cells which are rectangular in shape. It is few to many cells deep.
3. Cork cambium is meristematic in nature and cuts cork on the outer side and secondary cortex towards inner side.
4. Secondary cortex consists of thin walled parenchymatous, rounded or oval cells leaving many intercellular spaces. Cells are filled with many plastids.
5. Endodermis is present in the form of a single layer in young stages but at maturity it is not observed due to the formation of periderm.
Pericycle:
6. Single layered pericycle, consisting of barrel shaped cells, is clearly observed in young roots.
Vascular System:
7. Vascular bundles arc radial, exarch and show the secondary growth due to the presence of cambium.
8. Vascular tissues remain divided into many smaller groups with the help of broad medullary rays.
9. Vascular tissue consists of primary phloem, secondary phloem, cambium, secondary xylem, primary xylem and medullary rays.
10. Primary phloem is crushed and situated alternating with primary xylem groups.
11. Secondary phloem is more developed below the primary phloem. Phloem consists of sieve tubes, phloem parenchyma and companion cells.
12. Cambium is one to many celled thick, wavy and present in the form of a complete ring.
13. Secondary xylem is well developed and consists of tracheids, xylem parenchyma and large vessels.
14. Primary xylem group’s arc centrally located and face their groups towards periphery.
15. Medullary rays are parenchymatous, multiseriate and separate the vascular tissue in small groups.
Pith:
16. It is ill-developed.
Aerial Characters:
1. Pretence of lenucels
2. Well developed cork.
3. Chlorenchymalous secondary codex.
4. Absence of root hairs
Identification:
(a) 1. Presence of vessels in the xylem.
2. Vessels have perforated end walls with scalariform and regularly arranged holes. (Angiosperms)
(b) 1. Radial vascular bundles.
2. Protoxylem is exarch. (Root)
(c) 1. Vascular bundles are between 2-6.
2. Presence of cambium and secondary growth.
3. Reduced pith. (Dicotyledones)
4. Anatomy of Ficus – Root (Family – Moraceae):
It is circular in outline and reveals following tissues from outside with-in:
Periderm:
1. It is composed of cork, cork cambium and secondary cortex.
2. Cork is well developed and 6 to 8 or more layers are present. The cells are rounded, irregular or rectangular in shape and may be filled with tannin.
3. Cork cambium or phellogen is well developed and meristematic in function.
4. Secondary cortex or phelloderm is parenchymatous and the cells contain chlorophyll in young stages. The cells are rounded with many intercellular spaces in between.
5. Root hairs are absent.
6. Endodermis is well-developed, single layered and present in the young root but it gels crushed due to the secondary growth.
Pericycle:
7. Crushed due to secondary growth.
Vascular Tissue:
8. It is composed of crushed primary phloem, well developed secondary phloem, cambium, secondary xylem and primary xylem.
9. Primary phloem is radial to primary xylem and present in the form crushed patches. The number of the patches are as many as the number of xylem groups.
10. Secondary phloem ring is situated inner to the primary phloem. It consists of sieve tubes, companion cells and phloem parenchyma.
11. Cambium is present in the form of a continuous ring. But opposite to protoxylem, it is consumed in the production of medullary rays.
12. Secondary xylem is well developed and consists of large vessels, tracheids and xylem parenchyma.
13. Primary xylem bundles are centrally located, two to six or rarely more in number and facing their protoxylem towards the periphery, i.e., it is exarch.
Pith:
14. It is very small, parenchymatous and present in the centre.
Aerial characters:
1. Root hairs are absent
2. Well developed rough-type of cork.
3. Presence of lenticells.
4. Secondary parenchyma contains chloroplast.
5. Cuticle is present in young roots.
Identification:
(a) 1. Vessels are present in the xylem.
2. Vessels have perforated end scalariform and regularly arranged holes. (Angiosperms)
(b) 1. Radial vascular bundles.
2. Exarch protoxylem. (Root)
(c) 1. Vascular bundles are 2-6.
2. Presence of cambium and secondary growth.
3. Reduced pith. (Dicotyledones)