<P> A meristem is the tissue in most plants containing undifferentiated cells (meristematic cells), found in zones of the plant where growth can take place . Meristematic cells give rise to various organs of a plant and are responsible for growth . </P> <P> Differentiated plant cells generally cannot divide or produce cells of a different type . Meristematic cells are incompletely or not at all differentiated, and are capable of continued cellular division . Therefore, cell division in the meristem is required to provide new cells for expansion and differentiation of tissues and initiation of new organs, providing the basic structure of the plant body . Furthermore, the cells are small and protoplasm fills the cell completely . The vacuoles are extremely small . The cytoplasm does not contain differentiated plastids (chloroplasts or chromoplasts), although they are present in rudimentary form (proplastids). Meristematic cells are packed closely together without intercellular cavities . The cell wall is a very thin primary cell wall as well as some are thick in some plants . Maintenance of the cells requires a balance between two antagonistic processes: organ initiation and stem cell population renewal . </P> <P> There are three types of meristematic tissues: apical (at the tips), intercalary (in the middle) and lateral (at the sides). At the meristem summit, there is a small group of slowly dividing cells, which is commonly called the central zone . Cells of this zone have a stem cell function and are essential for meristem maintenance . The proliferation and growth rates at the meristem summit usually differ considerably from those at the periphery . </P> <P> The term meristem was first used in 1858 by Carl Wilhelm von Nägeli (1817--1891) in his book Beiträge zur Wissenschaftlichen Botanik ("Contributions to Scientific Botany"). It is derived from the Greek word merizein (μερίζειν), meaning to divide, in recognition of its inherent function . </P>

Three kinds of tissues do meristems develop into