What are vascular bundles?
Vascular bundles are a part of the transport system in vascular plants.
The two elements of the vascular tissue are xylem and phloem. These are arranged in groups called as vascular bundles.
Vascular bundles are classified based on different criterion
A) depending upon the presence or absence of cambrium they may be open or closed.
1)Open vascular bundles have the presence of a cambrium layer between the xylem and phloem. They show secondary growth.
2)Closed vascular bundles do not show secondary growth and are devoid of cambrium.
B) based on the arrangement of the elements within the plant body they are classified as radial or conjoint vascular bundles.
1) radial vascular bundles - the xylem and phloem are arranged separately along different radii. They are mostly found in the roots of plants.
2) conjoint vascular bundles - both the elements are arranged in the same radius and this is found in the stem and leaves.
They are further divided into
a)collateral vascular bundle: xylem is towards interior and phloem is arranged towards the exterior.
b)bi-collateral vascular bundle: phloem is present in two groups flanking the xylem.
c)concentric vascular bundle: when one element is surrounded by the other.
Apart from transport of food ( phloem ) and water ( xylem ) vascular bundles provide mechanical support to the plant.