Sketch the various types of vascular bundles.

Explanation

Vascular bundles are of the following two types :
(i) Radial vascular bundles : The xylem and phloem occur alternately in the form of separate vascular bundles. This type of vascular bundles is found in roots
(ii) Conjoint vascular bundles : The vascular bundles in which both xylem and phloem strands occur together. Conjoint bundles are of 3 types - collateral, bicollateral and concentric.

(i) Collateral vascular bundles : In these vascular bundles phloem lies on the outer side and xylem towards the inner side. These vascular bundles may be open or closed. Open vascular bundles have intrafascicular cambium while closed vascular bundles lack intrafascicular cambium.
(ii) Bicollateral vascular bundles : The vascular bundles which have phloem strands on both outer inner side of xylem are called bicollateral vascular bundles. Example : Cucurbita.
(iii) Concentric vascular bundles : Those vascular bundles in which one vascular tissue is surrounded by other, are called concentric vascular bundles. These are of following two types :
(A) Amphicribal : Xylem lies in centre and is surrounded by phloem.
(B) Amphivasal : Phloem lies in the centre and is surrounded by xylem.