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In this article we will discuss about the wood anatomy of some important plants:- 1. Dalbergia sissoo 2. Eucalyptus 3. Mangifera indica 4. Tectona grandis.
Dalbergia sissoo, Eucalyptus, Mangifera indica and Tectona grandis.
1. Dalbergia sissoo (Papilionoideae):
(a) Transverse Section of Stem:
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Wood of Dalbergia sissoo is purplish, diffuse porous with a clear distinction of sapwood and heartwood.
Some of its characteristic features are under-mentioned:
1. A multilayered cork, cork cambium and secondary cortex (Fig. 139A, B; constitutes the periderm which remains surrounded by a thick cuticle).
2. Pericycle is represented by a ring of sclerenchymatous patches and inner to these patches is present the crushed primary phloem.
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3. Secondary phloem and a compact cylinder of secondary xylem develop due to secondary growth.
4. Tracheids, vessels, xylem parenchyma and xylem fibers constitute the secondary xylem.
5. Because of vessels, the wood is porous. Vessels are large, numerous and present throughout the wood.
6. Vessels are usually filled with dark gummy- deposits, and growth rings are usually distinct in the wood.
7. Numerous narrow medullary rays traverse the phloem and xylem.
8. Sapwood and heartwood are clearly demarcated.
9. A small parenchymatous pith is located in the centre.
(b) R.L.S. Wood:
1. Vessels remain associated with living cells of parenchyma. They are large, quite broad and contain simple perforation plates.
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2. Dense and dark gummy deposits remain filled in vessels, but tylosis is absent.
3. Several medullary rays are present. In R.L.S. they are seen running at right angle to the long axis of the xylem elements (Fig. 139C).
(c) T.L.S. Wood:
1. In tangential longitudinal section (Fig. 139D) the wood shows large and broad vessels with simple perforation plates.
2. Living cells of parenchyma remain associated with vessels.
3. Uniseriate medullary rays are present. They are cut across the plane of the section.
4. Tylosis is not observed.
2. Eucalyptus (Myrtaceae):
Wood of Eucalyptus (Fig. 140) is diffuse porous with solitary vessels and biseriate medullary rays and vasicentric tracheids.
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It exhibits following details:
(a) Transverse Section of Stem:
1. It is circular in outline and remains surrounded by outer few layers of cork. Usually, two types of cells constitute the cork. Some are thick-walled, radially flattened and filled with resinuous substances, while other types of cork cells are thin-walled and hollow lacking resinuous substances.
2. Inner to the cork is present cork cambium followed by secondary cortex. Some scattered stone cells are present in the secondary cortex which is parenchymatous.
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3. Some sclerenchyma cells represent the discontinuous ring of pericycle.
4. Narrow and distinct medullary rays (Fig. 140 A, B) traverse through the continuous cylinders of secondary phloem and secondary xylem. Medullary rays connect the phloem to the pith.
5. Tracheids, vessels, xylem parenchyma and fibers constitute the secondary xylem.
6. Vessels are distributed uniformly in the wood, and the wood is thus diffuse porous. Sometimes, the vessels show oblique or radial pattern.
7. Vasicentric tracheids (short, thin and irregular- shaped) are also seen around the vessels.
8. Xylem parenchyma is present close to the vessels, i.e., paratracheal.
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9. Usually tyloses but sonietimes solid gummy deposits are seen in the vessels.
10. Clear annual rings are also present.
(b) R.L.S. Wood:
1. In radial longitudinal section (Fig. 140C), the vessels, tracheids, medullary rays and parenchyma cells are visible.
2. Vessels are very long (sometimes 2-5 metres), broad and usually solitary, and their end walls are simple and perforated. Simple pits and reticulate thickenings are also seen in the vessels.
3. Tracheids are short and irregular shaped.
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4. Medullary rays consist of two types of cells (heterocellular) and present at right angle to the long axis of xylem elements.
5. Parenchyma cells are seen associated with vessels.
6. Tyloses are present in some vessels, while in other vessels some gum deposits are present.
(c) T.L.S. Wood:
1. Vessels, uniseriate or biseriate medullary rays, tracheids and parenchyma cells are also seen in tangential longitudinal section of the wood (Fig. 140D).
2. Long and broad vessels are distributed throughout the wood almost uniformly. Tyloses and gum deposits fill the cavity of some vessels. Parenchyma cells are found associated with vessels.
3. In T.L.S., the medullary rays are cut transversely. They are uniseriate as well as biseriate. 4. Fibers are septate and thick-walled while tracheids are short and irregular.
3. Mangifera indica (Anacardiaceae):
Wood is moderately hard, light coloured, diffuse porous; contains tannin cells and resin canal; clearly demarcated sapwood and heartwood.
(a) Transverse Section of Stem:
1. Cork, cork cambium and secondary cortex form the periderm. One side of the cork cells consists of sclerotic walls.
2. Tannin cells, crystals, stone cells and resin canals are present in the cortex (Fig. 141 A,B).
3. The peripheral side of the each resin canal remains enclosed by an arc-shaped strand of fibres which represent pericycle.
4. Tannin sacs and fibres containing crystals are present in the region of secondary phloem
5. A continuous cylinder of secondary xylem is traversed by medullary rays.
6. Medullary rays are narrow, closely spaced, and unseriate or sometimes biseriate.
7. Vessels are angular, large, thin-walled, numerous and uniformly distributed throughout the wood. They make the wood diffuse porous.
8. Xylem parenchyma is large and paratracheal, i.e., found round the vessels.
9. Parenchymatous pith contains secretory ducts covered with epithelial cells.
10. Growth rings are clearly observed, and usually they are limited by xylem parenchyma.
(b) R.L.S. Wood:
1. Large and broad vessels with simple or sometimes scalariform perforation plates are present. Living cells of parenchyma remain always associated with vessels (Fig. 141C).
2. Medullary rays consist of two types of cells, and are seen at right angle to the long axis of xylem elements in R.L.S.
3. Fibres contain simple pits and septa.
4. Tyloses are inconspicuous and scanty.
(c) T.L.S. Wood:
1. Large and distinctly broad vessels with simple or scalariform perforation plates are also seen. Parenchyma cells also remain associated with the vessels (Fig. 141D).
2. The medullary rays are cut transversely. They are mostly uniseriate and only rarely biseriate.
3. Fibres contain simple pits and septa.
4. Tyloses are inconspicuous and scanty.
4. Tectona grandis (Verbenaceae):
Wood of Sagwan, a high-quality, timber-yielding plant, is ring-porous. It emits a leather-like odour, and its all the medullary rays are of one type.
(a) Transverse Section of Stem:
1. The stem is circular is outline (Fig. 142A, B) and remains surrounded by a few-layered zone of cork followed by cork cambium and secondary cortex. The endodermis and pericycle are not clearly demarcated.
2. During secondary growth, vascular cambium cuts secondary phloem towards outer side and secondary xylem towards inner side.
3- Wood or secondary xylem is formed by tracheids, vessels, xylem fibres and xylem parenchyma.
4. Due to the presence of vessels, the wood is said to be porous. Vessels present in the early-wood are very large and form conspicuous rings in this wood while those present in the latewood are small or only moderately large. The wood with these characteristics is called ring porous.
5. Distinct annual rings or growth rings (Fig. 142A.B) are seen in the wood. A gradual transition from early-wood to latewood is also visible.
6. Around the vessels is present a clear and thin sheath of wood parenchyma cells.
7. Medullary rays are 1-3 cells wide and are usually not very prominent.
8. Patches of primary xylem are present near the centrally located parenchymatous pith.
(b) R.L.S. Wood:
1. Vessels are quite broad and long (Fig. 142C) and their end walls are simple and perforated.
2. Parenchyma cells remain associated with vessels.
3. Usually tyloses and sometimes yellowish deposits are clearly seen in the vessels.
4. Medullary rays are broad, scanty and hetero- cellular, and are seen at right angle to the long axis of xylem elements in R.L.S.
5. Xylem fibres are septate and inter-vascular pittings are fine and alternate.
(c) T.L.S. Wood:
1. Tracheids, vessels, fibres and parenchyma are cut longitudinally in T.L.S. (Fig. 142 D).
2. Vessels are broad, connected end to end with perforated end walls, and the perforations are simple.
3. Tyloses and sometimes yellowish deposits are seen in the vessels.
4. Medullary rays are cut across in T.L.S. They are 1-3 cells wide and several cells long.
