Apical meristematic cells countinuously divide as long as the plants are alive. The activity of apical meristem drives the elongation of root and stem. The process of meristematic cell division which is responsible for the increasing in length or height is called primary growth.
Meristematic cell activity on root enables root to grow downward into the deeper soil layer. On the tip of the root there is a calyptra whose function is to protect root while anchoring into the soil.
|Primary Growth On Onion Root|
figure shows the cross section of onion root having primary growth. root can be distinguished into three zones (areas), zone of division, zone of elongation, and zone of differentiation.
Cell division zone is composed of root apical meristem and its derivative cells. New cells and root cap are produced from this zone.
In elongation zone, cell extention occurs by which the Length can be ten times longer than its intial length. The cells Are responsible for forcing the tip of the cell into the soil.
In differentiation zone, there are three tissue systems of mature plant, namely dermal tissue, primary tissue, and vascular tissue. Dermal tissue (epidermis) is produced by protoderm which is the outermost layer of meristem.
Primary tissue is the innermost layer of apical meristem. It Will differentiate into cortex and pith. Cortex is located between stele and epidermis. The innermost layer of cortex is bounded by a layer of cell called endodermis.
Vascular tissue (stele) is a transportation tissue that consists of primary Xylem and primary phloem. It is produced by procambium which is located between protoderm and primary meristematic tissue.