Lenticels are involved in

During secondary growth of plants,stem phellogen cuts off cells on both sides. The outer cells get differentiated into ...$A$... and the inner cells get differentiated into ...$B$... cortex.
Choose the correct combination of $A$ and $B$ with reference to the above statement.

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

Secondary growth is observed due to the activity of ..........

The best method to determine the age of a tree is:

Statement-$1$: Heartwood is more durable and resistant to the attacks of microorganisms and insects compared to sapwood.
Statement-$2$: Heartwood contains organic compounds like oils,aromatic substances,gums,resins,tannins,and phenols.