In dicot stem,secondary xylem lies towards the ...$A$... and secondary phloem lies towards the ...$B$.... Choose the correct combination of options for $A$ and $B$.

In old trees,the greater part of secondary xylem is dark brown and resistant to insect attack due to:
$(a)$ secretion of secondary metabolites and their deposition in the lumen of vessels.
$(b)$ deposition of organic compounds like tannins and resins in the central layers of stem.
$(c)$ deposition of suberin and aromatic substances in the outer layer of stem.
$(d)$ deposition of tannins,gum,resin and aromatic substances in the peripheral layers of stem.
$(e)$ presence of parenchyma cells,functionally active xylem elements and essential oils.
Choose the correct answer from the options given below:

Assertion : In woody stems,the amount of heart wood continues to increase year after year.
Reason : The cambial activity continues uninterrupted.

What do the following figures represent?

The secondary growth in the stem of $Cycas$ is brought about by:

What is the inner bark primarily composed of?