Substance in the cell wall of cork or bark that makes it impervious to water is suberin.

Explanation:
Cell wall is a rigid and protective layer which surrounds the plant cells. It provides mechanical support to the cell and protects it from the external environment. The cell wall of cork or bark is made up of a complex organic substance known as suberin. Suberin is a waxy, fatty material that is water repellent and resistant to decay. It is made up of long chains of fatty acids and glycerol, which are linked together by ester bonds.

Suberin is responsible for making the cell wall of cork or bark impervious to water. It acts as a waterproofing agent and prevents the movement of water and gases in and out of the cell. This property is essential for the survival of the plants, especially in arid or water-stressed environments.

Other substances found in the cell wall of plants are:
- Lignin: It is a complex polymer that provides strength and rigidity to the cell wall. It is responsible for the woody texture of stems and branches.
- Cutin: It is a waxy, water-repellent substance that covers the outer surface of leaves and stems. It prevents excessive water loss and protects the plant from pathogens and environmental stress.
- Pectin: It is a complex carbohydrate that forms a gel-like matrix in the cell wall. It helps to maintain the cell shape and structure, and also plays a role in cell-to-cell adhesion.

Conclusion:
Suberin is a complex organic substance found in the cell wall of cork or bark. It is responsible for making the cell wall impervious to water and prevents the movement of water and gases in and out of the cell. It is one of the essential components of the plant cell wall, which helps in the survival of the plants in water-stressed environments.