Xylem and Phloem are present in the form of bundles called vascular bundles.
1. Radial
2. Conjoint
3. Concentric.
1. Radial vascular bundle : Xylem and phloem are arranged in an alternate matter or different radii are called Radial vascular bundle.
Eg: roots
2. 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 bundle.
Eg: Cucurbita.
3. 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