Commercial cork is obtained from

In dicot stem,secondary growth is due to the activity of:

Secondary growth does not occur in monocot stems because the vascular bundles are .....

Which of the following is responsible for the formation of cork cambium?

Tissue present in an annual ring is

$A$ nail is driven into the trunk of a $30$ year old tree at a point $1$ meter above the soil level. The tree grows in height at the rate of $0.5$ meters a year. After three years,the nail will be