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Q.
In the stem of Dracaena, what type of vascular bundles are seen?
NTA AbhyasNTA Abhyas 2020
Solution:
The vascular bundle includes the vascular tissues or the conducting elements of the plant. They typically have:
xylem (also called has wood, or hadrome), which is made up of vessels, trachaea, xylem parenchyma and fibres. These help in ascent of sap. Typically, they are adaxial in position.
phloem (also called bast, or leptome), which is made up of sieve elements, companion cells, phloem parenchyma, fibres. They help in translocation of food. Typically, they lie abaxially.
they may (or may not as well) have cambium, which are meristematic tissue
Depending on the arrangements, they may be of the following types:
Simple VB (acronym of vascular bundle) or radial VB has alternate xylem and phloem. It is found in roots.
Compound VB has both xylem and phloem at one row or column.
The compound VB may have:
Concentric arrangement of xylem and phloem. When the phloem encircles the xylem, it is called hadrocentric or amphicribal VB, as in Pteris. When the xylem encircles phloem, it is called leptocentric or amphivasal, as in Dracaena.
The VB may have conjoint arrangement. When xylem and phloem lie at the same plane, it is called conjoint, collateral. If cambium is present between xylem and phloem, it is called conjoint, collateral, open. It is closed VB, when cambium is absent between xylem and phloem. A VB may be bi-collateral, where the sequence is phloem > cambium > xylem > cambium > phloem. It is always open type.