In a stem which is covered by periderm and in which stomata are absent,gaseous exchange takes place through

Bark refers to all tissues exterior to the

$A$: Bark is all the tissues outside the vascular cambium.
$R$: Bark is formed due to the activity of phellogen only.

The vascular cambium produces . . . . . . .

Which of the following meristems is responsible for the formation of the extra-stelar secondary growth in a dicot stem?

$I.$ Annual rings are formed as a result of seasonal environmental conditions.
$II.$ Tracheids/vessel elements are larger during periods when water is abundant.
$III.$ Tracheids/vessel elements have thicker walls during periods of water deprivation.
$IV.$ Wood formed in previous years is always darker than newer wood.
Select the combination of correct statements from the options given below.