What is correct for heartwood?

The tissue made up of thin-walled rectangular cells responsible for the secondary growth is

Vascular cambium in dicot root develops from

The pores present in the wall of a plant's stem are called...

The position of xylem in secondary xylem is:

Read the components $a$ to $d$ given in the note and identify the correct sequence of components from the outside to the inside of a mature stem:
$(a)$ Secondary cortex
$(b)$ Wood (Secondary xylem)
$(c)$ Secondary phloem
$(d)$ Phellem (Cork)