Open vascular bundles lack .......... .

Lenticels are ...........

Which of the following is incorrect regarding heartwood?

$I.$ 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.

Describe the contribution of cork cambium in secondary growth.

Grafting is successful in dicots but not in monocots because the dicots have