Wood is $.....................$

Secondary growth is absent in

Heartwood differs from sapwood in

The position of xylem in secondary xylem is:

Narrow bands of parenchymatous tissue which pass through the secondary xylem and phloem radially are called

$A$ transverse section of the trunk of a tree shows concentric rings which are known as growth rings. How are these rings formed? What is the significance of these rings?