ADVERTISEMENTS:
The following points highlight the top two types of monocot and dicot roots. The types are: 1. Anatomy of Dicotyledonous Roots 2. Anatomy of Monocot Root.
Monocot and Dicot Roots: Type # 1.
Anatomy of Dicotyledonous Roots:
I. Cicer- Root:
ADVERTISEMENTS:
It is circular in outline (Fig. 170) and reveals following tissues from outside with-in:
Epiblema:
1. It is the outermost layer consisting of many thin-walled cells.
2. From some of its cells arise unicellular hair.
ADVERTISEMENTS:
3. Cuticle is absent.
Cortex:
4. It is very large, parenchymatous and well- developed occupying the large 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 roots, 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 those opposite to the protoxylem, are thin-walled and have been termed as passage cells.
ADVERTISEMENTS:
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 cells.
Vascular Bundles:
ADVERTISEMENTS:
13. The vascular bundles are 2 to 6 and radial, i.e., xylem and phloem present 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.
ADVERTISEMENTS:
17. Metaxylem strands are big, present towards the centre and are made up of large reticulate and pitted vessels.
18. In some cases the metaxylem meet in the centre and thus obliterate the pith.
19. Phloem is made up of sieve tubes, companion cells and phloem parenchyma.
20. In mature roots, cambium also appears cutting the secondary structures.
ADVERTISEMENTS:
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 vessles in the xylem.
2. Vessels have perforated end walls with scalariform and regularly arranged holes …………….Angiosperms
ADVERTISEMENTS:
(b) 1. Presence of unicellular root hair.
2. Vascular bundles are radial and xylem is exarch. …………Root
(c) 1. Vascular bundles are 2-6.
2. Reduced pith……………………………. Dicotyledons
II. Tinospora-Root:
ADVERTISEMENTS:
T.S. appears circular in outline and reveals following tissues (Fig. 171) 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 visible 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 are radial, exarch and show the secondary growth due to the presence of cambium.
8. Vascular tissue remains divided into many smaller groups due to the presence 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 is present alternate with primary xylem groups.
11. Secondary phloem b mam developed below the primary phloem. Phloem consists of sieve tubes, phloem parenchyma and companion cells.
12. Cambium is one to many cells-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 groups are 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. Presence of lenticels.
2. Well-developed cork.
3. Chlorenchymatous secondary cortex.
4. Absence of root hair.
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……………………………………. Dicotyledons
III. Ficus-Root:
It is circular in outline (Fig. 172) 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 its 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 hair are absent.
6. Endodermis is well-developed, single-layered and present in the young root but it gets crushed due to the secondary growth in later stages.
Pericycles:
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 of 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 hair are absent.
2. Well-developed, rough-type of cork.
3. Presence of lenticels.
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 walls with scalariform and regularly arranged holes……………….. Angiospera
(b) 1. Radial vascular bundles.
2. Exarch protoxylem…….. Root
(c) 1. Vascular bundels are 2-6.
2. Presence of cambium and secondary growth.
3. Reduced pith………………………………. Dicotyledos
Monocot and Dicot Roots: Type # 2.
Anatomy of Monocot Root:
Zea mays-Root:
It is circular in outline and reveals the following tissues (Fig. 173) from outside with-in:
Epiblema:
1. Single-layered epiblema consists of barrel- shaped or rounded cells.
2. From some cells arise unicellular hair.
Cortex:
3. It is well-developed, several cells deep and parenchymatous.
4. The cells are thin-walled, rounded in shape and leave many intercellular spaces.
5. Just below the epiblema are present 2 to 6 layers of collenchyma in old roots. This represents exodermis.
6. Remaining part of the cortex is parenchymatous.
7. Endodermis is the innermost layer of cortex. It consists of many compactly arranged, barrel- shaped cells.
8. Casparian strips are present on the radial and transverse walls of the endodermal cells.
9. Thin-walled endodermal cells are known as passage cells. They lie opposite to protoxylem.
Pericycle:
10. Single-layered pericycle consists of thin-walled cells and present inner to the endodermis.
Vascular Tissue:
11. It is composed of alternating strands of phloem and xylem.
12. Vascular bundles are radial, exarch and polyarch. Cambium is absent.
13. Xylem consists of vessels, tracheids and xylem parenchyma.
14. Protoxylem elements are towards the outer side, i.e., exarch, small in diameter and their walls have thickenings.
15. Metaxylem vessels face towards the centre and have larger diameter. Innermost metaxylem vessel is very large and spherical or oval.
16. Phloem consists of sieve tubes, companion cells and phloem parenchyma. It exhibits exarch condition with its protophloem towards the periphery and metaphloem towards the centre.
17. Thick-walled, sclerenchymatous conjunctive tissue is present in between the vascular bundles.
Pith:
18. It is well-developed and parenchymatous.
19. The cells are round in shape and leave many intercellular spaces.
Identification:
(a) 1. Vessels are present in the xylem.
2. Vessels have perforated end walls with Scalariform or regularly arranged holes……………….. Angiosperms
(b) 1. Vascular bundles are radial.
2. Exarch protoxylem……………………………………….. Root
(c) 1. Vascular bundles are more than 6.
2. Absence of Cambium.
3. Well-developed pith…………………….. Monocot
