Meristems on basis of origin: Depending upon the mode of origin, meristems are classified into three types:
(i) Promeristem : (a) Promeristems are also called primordial meristems or embryonic meristems. (b) These are localized groups of meristematic cells in germinating embryos or young seedlings, (c) Promeristems give rise to primary meristems where formation of new organs is initiated
(ii) Primary meristems : (a) These are the meristems, which are derived from the promeristems and retain the capacity to divide throughout the life of the plant, (b) They are represented by apical meristem, intercalary meristem and intrafascicular cambium, (c) the primary meristems form different primary permanent tissues, (d) The intrafascicular cambium, produces secondary vascular tissues and medullary rays.
(3) Secondary meristems: (a) These are the meristem, which are formed from permanent tissues by the process of differentiation, (b) They are represented by interfascicular cambium, vascular cambium, cork cambium or phellogen, wound cambium and accessory cambium, (c) They all are lateral in position and give rise to secondary permanent tissues that result in radial growth.