Term Meristems was given by Nageli, it means juvenile/young tissues.
Cells of these tissues have the ability to divide. These cells are thin-walled, living, having dense protoplasm, conspicuous nucleus, and are in an active state of metabolism.
ON THE BASIS OF ORIGIN:
Meristems are 3 types:
- PROMERISTEM: Also referred as embryonic meristem. Present at the apices of the shoot and root tip. It divides to form primary meristem.
- PRIMARY MERISTEM: Found below the pro-meristem in the shoot and root tip & intercalary meristem. They divide to produce primary permanent tissue that forms the primary plant body.
- SECONDARY MERISTEM: It is formed later in the plant body. It develops from primary permanent tissue due to dedifferentiation. They divide to produce secondary permanent tissue that forms the secondary plant body. They are interfascicular cambium & cork cambium.