<P> A group of cells which are similar in origin; similar in structure and similar in function are called simple permanent tissue . They are of four types: </P> <Ol> <Li> Parenchyma </Li> <Li> Collenchyma </Li> <Li> Sclerenchyma </Li> <Li> Epidermis (botany) </Li> </Ol> <Li> Epidermis (botany) </Li> <P> Parenchyma (para -' beside'; enchyma -' tissue') is the bulk of a substance . In plants, it consists of relatively unspecialised living cells with thin cell walls that are usually loosely packed so that intercellular spaces are found between cells of this tissue . This tissue provides support to plants and also stores food . In some situations, a parenchyma contains chlorophyll and performs photosynthesis, in which case it is called a chlorenchyma . In aquatic plants, large air cavities are present in parenchyma to give support to them to float on water . Such a parenchyma type is called aerenchyma . some of parenchyma cells have metabolic waste and is known as idioblast . Spindle shape fibre also contained into this cell to support them and known as prosenchyma, succulent parenchyma also noted . </P>

What are the main functions of the three plant tissue systems