Collenchyma cells are elongated cells with irregularly thick cell walls that provide support and structure. Their thick cell walls are composed of the compounds cellulose and pectin. The role of this cell type is to support the plant in axes still growing in length, and to confer flexibility and tensile strength on tissues. These cells help to support plants while not restraining growth due to their lack of secondary cell walls and the absence of a hardening agent in their primary cell walls. These cells are often found under the epidermis, or the outer layer of cells in young stems and in leaf veins.
Like Parenchyma, collenchyma may also contain chloroplasts or may regain the thickening. Intercellular spaces may or may not be present. Three forms of collecnchyma are recognized based on the types of thickenings –
- Lamellar collenchyma -Thickening on the tangential wall
- Angular collenchyma – Deposition of pectin in the corners where several cells meet
- Lacunar collenchyma -Thickenings around the intercellular spaces
The primary wall lacks lignin that would make it tough and rigid, as such this cell type provides what could be called plastic support – support that can hold a young stem or petiole into the air, but in cells that can be stretched as the cells around them elongate.