Classify meristem on the basis of origin.
The meristem originates from embryo. It is called promeristem or embryonic meristem. On the basis of origin meristem can be primary meristem and secondary meristem.
(i) Primary meristem is composed of cells which are direct descendants of embryonic cells. These cells are always in active state of division and give rise to primary permanent tissues.
(ii) Secondary meristem is formed when some living permanent cells regain the power of cell division.