(i) Collateral: It is a type of conjoint vascular bundle where xylem is arranged towards the interior (adaxial) and the phloem arranged towards the exterior (abaxial). In this Vascular bundle, only one patch of xylem and one patch of phloem are present. Conjoint collateral vascular bundle can be divided into two types on the basis of cambium, such as-
- Open: Cambium is present between xylem and phloem, e.g., Dicot stem (Mangfera indica)
- Closed: Cambium is absent between xylem and phloem, e.g., Monocot stem (Oryza sativa)
(ii) Bi-collateral: In this type of vascular bundle, xylem is placed in the middle and there are two patches of phloem and cambium tissue at each side. In this type of conjoint vascular bundle, phloem is present in two groups, one outside the xylem and the other inside the xylem (i.e., xylem is located between two strands of phloem). Thus the vascular bundle will have outer phloem, outer cambium, xylem, inner cambium and inner phloem, e.g., Dicot stem.