Explain the following terms: a.Epidermis b.Cortex …

Vascular bundles wherein xylem and phloem lie side by side are called as radial bundles while conjoint vascular bundles have xylem and phloem separated from one another as are found in leaves.
A conjoint vascular bundle can be collateral or bicollateral. Collateral vascular bundles have xylem and phloem arranged in same radium with xylem present towards the inner side and phloem towards the outer side. Bicollateral bundles have phloem on both sides of the xylem as compared to collateral bundles wherein phloem is present on one side of xylem only. In leaves, xylem is present near upper epidermis and phloem near the lower one with phloem on one side of xylem thus collateral, not bicollateral bundles. On the basis of the presence of absence of cambium, collateral bundles are grouped as open or close bundles, those with cambium are termed as open vascular bundles while the vascular bundles without cambium are termed as closed.
Leaves lack cambium in vascular bundles making them closed type, this vascular bundles in leaves are found irregularly scattered in the mesophyll with the largest and the oldest one at centre and is termed as midrib vein. Each vascular bundle has a bundle sheath of compactly arranged barrel shaped parenchyma cells which cover both xylem and phloem. Xylem is present near upper epidermis and phloem near the lower one. Xylem has protoxylem and metaxylem vessels with protoxylem present towards upper epidermis, thus conjoint, collateral close vascular bundle with endarch xylem.