The xylem which is functional in a dicot tree is

$A$ : Oldest layer of sapwood lies just outside vascular cambium.

$R$ : Sapwood contains actively conducting vessels and occupies central part of stem.

$I.$ Annual rigs are formed as a result of seasonal environmental conditions

$II.$ Tracheids/vessels elements are larger during periods when water is abundant

$III.$ Tracheids/vessels elements have thicker wall during periods of water deprivation

$IV.$ Wood formed in the previous years is darker than newer wood

Select the combination of correct statements from the options given below

Identify the correct order of the components with reference to their arrangement from outer side to inner side in a woody dicot stem.

$I.$ Secondary cortex

$II.$ Autumn wood

$III.$ Secondary phloem

$IV.$ Phellem

Cambium activity is

When secondary growth in thickness is initiated in a dicot root, which of the following happens first