Define collateral vascular bundle.

Hint: It is a type of vascular bundle in which a strand of phloem is present external to the strand of xylem on the same radius side by side. Here the phloem occurs on one side of the xylem strand.

Complete Answer:
- A vascular bundle is a part of the transport system in vascular plants. The transport itself happens in vascular tissue, which exists in two forms: xylem and phloem.
- Both these tissues are present in a vascular bundle, which in addition will include supporting and protective tissues.
- The xylem and phloem are generally present together in vascular bundles that lie in various positions associated with each other.
- The xylem is closer to the centre of the stem or root whilst the phloem is closer to the external.
- In a leaf, the ventral surface of the leaf will commonly be the above, with the ventral surface at the bottom. Vascular bundle are four types, they are- collateral Bundle, bicollateral Bundle, concentric Bundle and radial Vascular Bundle.
- In the collateral vascular bundle, phloem and xylem are aligned side by side in the similar radius. Usually, xylem is to the inner side whereas phloem is towards the outer side. There are two types of the collateral vascular bundle, open and closed.

Note: In a vascular plant, vascular bundle is a division of the transport system. Both vascular tissues (xylem and phloem) are located in a vascular bundle as well as it also function as protective tissues. An open collateral vascular bundle has cambium and fascicular cambium between xylem and phloem. The bundles can rise in diameter by regular secondary development with the support of fascicular cambium.