The vascular cambium produces . . . . . . .

The cork cambium (phellogen) is formed from:

Which of the following pairs is correct in the study of secondary growth?

Some vascular bundles are described as open. This is because they:

$I.$ It is resistant to microorganisms
$II.$ It comprises dead elements
$III.$ It comprises highly lignified cell wall
$IV.$ It is the peripheral part
$V.$ It is dark and tough
Which of the above property does not belong to heartwood?

$A$. Heartwood is durable,dark,and central in position.
$B$. Tyloses are balloon-like structures of xylem parenchyma in vessel lumen.
$C$. Late wood is formed during spring season.