Meristematic areas and growthPrevious revision of Idaho Master Gardener Program Handbook Chapter 3 Basic Botany. page 3-15
Plants have specific meristematic areas where cells actively divide to provide more cells that will expand and develop into other tissues and organs of the plant.
Shoot meristems are at the very tips of the above-ground parts of the plant. They produce new buds and leaves in a particular pattern at the tip of the stems. The shoot meristem produces cells that eventually form the different tissues of the stem: the epidermis and the very first xylem and phloem. In some plants, this meristem will produce flower buds at a certain point in the development of the plant. In other plants, this meristem continues to produce only vegetative structures (leaves and stems). If this is the case, flowers are produced on side branches in the axils of leaves some distance below the apex. The shoot meristem allows the plant to grow and increase in height.
Another type of apical meristem is the root meristem, located at the tips of roots. The root meristems provide for elongation of the roots and produce the cells that will become the epidermis, cortex, and the xylem, cambium, and phloem of the mature root.
Lateral meristems are cylinders of actively dividing cells that start just below the apical meristems and are located up and down the plant. One type of lateral meristem is the vascular cambium, which produces new xylem and phloem. Another lateral meristem is the cork cambium, which produces bark on older stems and roots. The stem girth of woody perennial plants increases by the activity of these meristems.
- Other types of meristems:
Some plants have a subapical meristem that produces new cells in the region just behind a shoot meristem. Plants that form rosettes when they first produce leaves and then "bolt" when producing a flowering stalk have subapical meristems. An example is common mullein. The subapical meristem aids in formation of the flowering stalk.
Some other plants, mostly monocots, have active meristematic cells in older mature tissue, separated from the shoot meristem. For example, grasses have intercalary meristems just above the nodes in the lower region of the leaf sheaths. These cells divide and provide the growth of the grass leaf from the base. Intercalary meristem cells divide and produce new growth from the leaf base, giving grasses the unique ability to regrow after mowing or grazing.