All types of cells that make up a plant originated from meristematic tissues, formed by cells that have a thin primary wall, small vacuoles, and a large capacity for mitosis.
Differentiated tissue cells, even though they did not die during differentiation (such as super, xylem, for example), lose their ability to multiply by mitosis. Meristematic cells multiply and differentiate, giving rise to the various permanent tissues of the plant, whose cells no longer divide.
At certain plant sites, such as the root and stem apexes, there are meristematic tissues that descend directly from the first embryonic cells present in the seed. These are the primary meristems.
The stem grows in length thanks to the activity of a primary meristem present at its apex, the stem apical meristem. The meristem responsible for root length growth is not terminal, but is protected under a cellular hood called coif. That's why it's called root subapical meristem.
Secondary meristems are those that arise from differentiated, usually parenchymal, cells that regain mitotic capacity, a phenomenon that botanists call undifferentiation. The felogen that makes up the peridermis, for example, is an example of a secondary meristem, which arises from the de-differentiation of parenchymal cells located under the epidermis. The multiplication of the cells of the felogen gives rise to the feloderm and the sub that make up the periderm.