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

In old trees,the greater part of secondary xylem is dark brown due to the

$I.$ 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.

Growth rings are well marked in trees growing in

In dicots and gymnosperms,secondary growth is caused by:

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