When component cells of the tissue contain chloroplast it is called chlorenchyma. They help in photosynthesis. Palisade parenchyma and spongy parenchyma of mesophyll tissues are chlorenchymatous.
When intercellular spaces are well developed in a parenchyma, it is called aerenchyma. They are interconnected. Air spaces are generally schizogenous in origin. They are found in aquatic plants and provide buoyancy to the plant.
Parenchyma cells containing ergastic substances are called idioblasts. Tannin cells, cells filled with raphides, etc. constitute idioblast.
In some cases the cells are long and taper at either ends (as in pericycle of some plants). This is called a prosenchyma
This tissue has manifold functions
(i) It performs physiological functions like photosynthesis, secretion, assimilation and storages.
(ii) Aerenchyma provides buoyancy to hydrophytes and also helps in gaseous exchange.
(iii) It helps in healing of wound and regeneration of organs.
(iv) Prosenchyma provides strength and helps in conduction.
(v) It helps in formation of adventitious roots and buds.
Above all, parenchyma is considered as the most fundamental tissue as it is the precursors of other cell types. When a meristematic cell divides, one of the daughter cells first becomes converted to parenchyma and then to other cell types.
All primitive plants are composed of only parenchyma. It is the tissue where cells sometimes become meristematic and secondary meristem originates from this tissue.