Explain the types of vascular bundles.

Explanation

Xylem and phloem are present in the form of bundles called vascular bundles.
(i) Radial, (ii) Conjoint, (iii) Concentric.
(i) Radial vascular bundle: Xylem and Phloem are arranged in an alternate matter or different radii are called Radial vascular bundle. Eg: roots.
(ii) Conjoint vascular bundle: Xylem and phloem are arranged in the same radius are called conjoint vascular bundle.
Divided in two types:
(a) Collateral vascular bundles: Xylem and phloem are arranged in the same radius with phloem towards the outside is called collateral vascular bundles. Eg: stem and leaf.
Collateral vascular bundles are of two types :
Open collateral vascular bundle : Vascular bundle consists of cambial tissue in between xylem and phloem are called Open collateral vascular bundle. Eg: Dicot stem
Closed collateral vascular bundle: Cambium is absent in vascular bundle are called Closed collateral vascular bundle Eg : Monocot stem
(b) Bicollateral : Phloem occurs on both the outer and inner side of xylem. This vascular bundle is Bicollateral vascular bundlr. Eg: Cucurbita.
(iii) Concentric vascular bundle: The vascular bundle in which either phloem surrounds the xylem or xylem surrounds the phloem completely called Concentric vascular bundles. It is of two types: (a) Amphivasal (b) Amphicribral.
(a) Amphivasal: The Xylem completely surrounds the phloem. Eg: Dracaena
(b) Amphicribral: The phloem completely surrounds the Xylem. Eg: Ferns
Exarch : Protoxylem vessels are present towards the periphery and meta xylem towards the centre. Eg Root
Endarch : Protoxylem are present towards the centre and meta xylem towards the periphery. Eg: Stem