Meristem

Meristems are the growing tips of roots and shoots, where cells are actively dividing and forming new plant tissue.

When plant cells first form, while they are youthful, they are not specialized, or differentiated. These are called apical meristems. At first, they can continue to divide and form more new. undifferentiated cells. Then, they are triggered to become specific, specialized cells.

Shoot apical meristems of Jade plant (left). Two weeks later, leaves have developed (right). (Daniel,levine) CC BY-SA 3.0

Apical meristem tissue can differentiate into three specializations:

• Protoderm - these cells turn into the outer layer of stems and leaves
• Procambrium - these cells develop into the xylem and phloem (vascular bundles), cork, and lateral roots; they can also persist in the rings of woody plants to create new vascular bundles each year
• Ground meristem - these cells become the outermost layer (bark) of the main plant body

There are also secondary, or lateral, meristems programmed to expand the plant outwards.

Meristem tissue found at the tips of stems is called shoot apical meristems. This is where the cotyledon, leaves, buds, petals, sepals, seeds and all the other above ground plant cells are formed. Many herbicides work by halting meristem tissue cell production Root apical meristem tissue makes new roots and tubers.

If you have access to a microscope, you can actually see these individual meristem cells!