QS Study

Extra-stelar secondary growth of the dicot stem is discussed below under the two headings:

Formation of periderm:

i) At the advent of extra-stelar secondary growth, the cells of the outer most layer of the hypodermis turn into phelogen or cork cambium after having incapable of cell division.

ii) The cells of the phelogen or cork cambium undergo division and form cork cells or phellem totsards the penpheral region and pheloderm or secondary cortex towards the inner side. When one cork cambium causes its function, another new one appears in the inner tissues

Formation of bark:

i) Due to the presence of subenn in the walls of cells water cannot enter into them.

ii) As the cork cells do not get any Supply of water and food from the inner conducting tissue, they gradually dry up and die and the cells are commonly known as bark ‘finis, the dead cells form a hard layer around the stem “Ibis hard wet which Is formed outside the cork cambium or phelogen is known us bark.

The bark is of two types, such as- Scally hark- Guava, Pins plant etc

Ringed bark- Mango, lichi etc.


i) It protects the plant from excessive heist and cold

ii) It reduces the rate of evaporation

iii) It protects the inner tissues from dryness

iv) It protects the inner tissues from external hurt and the attack of fungi and bacteria.

v) It also gives a little mechanical support.