With the help of a neat labeled diagram, explain structure and any one function of collenchyma.

Explanation

Collenchyma is defined as a simple , permanent and living mechanical tissue . It occurs in hypodermal regions of young dicot stem and bundle sheath extension of dicot leaf. It is a highly restricted tissue and totally absent in roots and monocot plants.
Characters :
1. Cells appear usually oval or spherical .
2. Cells are compactly arranged without intercellular spaces except lacunar type.
3. The cell wall is made up of cellulose and pectin.
4. The cell walls show uneven thickening specially at corners.
5. Cells have cytoplasm and nucleus and hence are called living cells.
6. Cells have large and prominent vacuolse.
Types :
Based on the pectin deposition , collenchyma is of the following three types .
(a) Angular collenchyma - Here pectin is deposited in the angles or intercellular spaces of cells. eg. Datura . Ficus etc.
(b) Lamellar collenchyma : Here pectin is deposited in between the cellular layers int he form of sheets . eg. Radish, Sunflower etc.
(c) Lacunar collenchyma - Here pectin is deposited along the sidewalls around the intercellular space leaving a small space in the centre. eg. Malva , Althea etc.
Functions :
1. Collenchyma gives mechanical support.
2. Cells posses chloroplasts in young stems and help in photosynthesis.
3. Cells become meristematic and help in the secondary growth.
4. In young parts of dicot plants , it give resistance against the pulling and bending actions of wind .