noun, plural: primary meristems
(botany') A type of meristem that is involved in the primary growth and thus gives rise to the primary tissues of the plant
A meristem is comprised of indeterminate, actively dividing cells that give rise to differentiated permanent tissues such as epidermis, trichomes, phellem, and vascular tissues. A meristem may be primary or secondary. A primary meristem is a type of meristematic tissue that is responsible for the primary growth. Primary growth is a growth in length. It is responsible for the increase in the height of a plant as opposed to the increase in diameter, which is the role of secondary growth. The primary meristem is also responsible for giving rise to the primary permanent tissues of the plant. Some of the primary meristematic cells may produce cells that become permanent tissues, e.g. dermal, ground, and primary vascular tissues.
The primary meristem, as a meristematic tissue, is comprised of undifferentiated (others, partially differentiated), embryonic cells. They are actively dividing cells, with thin walls and large nuclei. These cells do not form secondary cell wall thickenings, and therefore have only primary cell walls. An example of a primary meristem is the apical meristem. Apical meristems are meristematic tissues located in the apices of plant, e.g. root apex and shoot apex.