The parenchyma cells are permanent simple tissues of the plants consisting of thin-walled living cells. In some parenchyma tissues, intercellular spaces may be well-developed into air cavities and form a connected system throughout the entire plant body. The parenchyma tissues having air cavities called aerenchyma. This type of tissue is found in many aquatic plants that help to float to the upper surface of the water.

The parenchyma cells are permanent simple tissues of the plants consisting of thin-walled living cells. Some parenchyma cells contain leucoplastids which serve to store reserve materials in solution within the vacuoles or in the form of solid particles in the cytoplasm. Such specialised parenchyma cells which contain oil, tannins and calcium oxalate crystals are called idioblast. These types of cells differ from the neighbouring cells in size, contents and function.

Parenchyma is a primary, simple permanent tissue of the plants consisting of thin-walled cells. The cells of this tissue are living and more or less isodiametric in shape with intercellular spaces. The cell wall is usually thin and composed of cellulose. Different types of parenchyma are present in plants that contain chloroplasts with chlorophyll (chlorenchyma), air cavities (aerenchyma), oil, tannin, calcium oxalate (idioblast), etc. The main functions of parenchyma are the storage of food, photosynthesis, conduction of water (by xylem and phloem parenchyma), wound recovery, etc.

The permanent simple tissue consisting of slightly elongated cells whose primary walls are unevenly thickened is called collenchyma. The unevenly thick cell wall is made up of cellulose, hemicellulose and pectin materials. The thickening of the cell wall generally occurs at the corners where a number of cells join with each other. Primary pit fields may be distinguished in the collenchyma cell wall. These cells are living and containing vacuolated protoplasm. On the basis of thickening pattern, collenchyma tissues are classified into angular collenchyma (thickening are localised at the corners), lacunate collenchyma (thickening on the walls around the intercellular spaces) and plate collenchyma (thickening on tangential wall).

Complex tissues are heterogeneous in nature and are composed of different types of cell components. Xylem and phloem are the complex tissues that together form the vascular bundles. The xylem consists of four types of tissues such as tracheids, xylem vessels, xylem fibres and xylem parenchyma. Tracheids, vessels and fibres are dead and elongated cells that help in the transportation of water and minerals and provide mechanical support to the plants. Xylem parenchyma is the living, thin-walled cells that involved in water conduction and act as a storage tissue.