Explain the process of secondary growth in the stems of woody angiosperms with the help of schematic diagrams. What is its significance? Why it does not take place in monocotyledonous plants?
The growth of the roots and stems in length with the help of apical meristem is called the primary growth.
Apart from primary growth most dicotyledonous plants exhibit an increase in girth. This increase is called the secondary growth.
The tissues involved in secondary growth are the two lateral meristems: vascular cambium and cork cambium.
Vascular Cambium: The meristematic layer that is responsible for cutting off vascular tissues – xylem and pholem – is called vascular cambium. In the young stem it is present in patches as a single layer between the xylem and phloem. Later it forms a complete ring.
In dicot stems, the cells of cambium present between primary xylem and primary phloem is the intrafascicular cambium. The cells of medullary cells, adjoining these intrafascicular cambium become meristematic and form the interfascicular cambium. Thus, a continuous ring of cambium is formed.
Cork Cambium: As the stem continues to increase in girth due to the activity of vascular cambium, the outer cortical and epidermis layers get broken and need to be replaced to provide new protective cell layers. Hence, sooner or later, another meristematic tissue called cork cambium or phellogen develops, usually in the cortex region.
Secondary growth in stem has been explained in the animation in our study material at the following link, please go through that and if you have any doubts then get back to us.