Role of Cork cambium or Phellogen in secondary growth in Dicot stem

Formation of cork cambium or phellogen  

• Continuous formation  of secondary vascular tissue inside the stem causes stretching of cortex. 

• As a result, outer layer of cortex is differentiated and form cork cambium. It is mostly developed from cortex.

Remember 👌👌 In Nerium Pear, cork cambium is developed from epidermis and Hypodermis respectively.

• The cells of cork cambium become more meristmatic and intercellular spaces soon are disappeared. 

Activity of cork cambium: 

• The cells of cork cambium are capable to divide on both outer and inner side. 

• The cells that are formed on outer side, devoid of intercellular spaces and filled with tannin and die. 

• The suberised dead cells that are also formed on outer side called Phellem or cork.

• In some species  of  plants,  cork is peeled up due to internal pressure. In some plants , a very thick layer of cork is formed. Such cork is exploited commercially. 

• Commercially cork is obtained from the  cork oak or Quercus suber. 

• Cork is impervious to water and air therefore it form impervious insulating layer around the trunk. 

• Microbes and insects are not capable to attack on plant due to presence of cork.

• The cells that are formed on inner side of cork cambium, made up of parenchyma and collenchyma.

• They form secondry cortex or phelloderm. They have chloroplast.

Phellogen or cork cambium,  phellem or cork,  and phelloderm or secondary cortex collectively form periderm.

• Term Bark is used for different tissue of stem  outside the vascular cambium. 

• It consists of all the tissue outside the vascular cambium such as secondary phloem, cortex and periderm. 

• Outer bark has periderm only whereas secondary phloem and  cortex form inner bark. 

• The bark formed at spring season called early or soft bark and the bark formed at late season called hard bark.

• Formation of lenticels : 
• These are large sized aerated pore formed in cork or phellem for gaseous exchange. 

• These are present in all type of phellem including stem, root potato tuber etc. These are scattered or arranged in row. 

• The interior of lenticels is filled  with suberised or non suberised cells called complementary cells.  

• Lenticels may closed in extreme winter by the formation of suberised closing cells.