Plant Root Growth

It is easy to assume that plant growth occurs evenly all over the surface. This is not the case. It is confined to specific areas and occurs through cell division and cell elongation.


CELL DIVISION
Growth begins with cell division by a process called MITOSIS. The principal type of growth, or PRIMARY (vertical) growth, occurs at the tips of the roots (and shoots) in APICAL MERISTEMS. As you can see, this region is a short distance back from the root (and shoot) tip(s).

The root apical meristem is protected by a specialised layer of hardened cells called the ROOT CAP.

CELL ELONGATION
Once divided, the new cells elongate, forcing the root cap through the soil/compost. Physical growth now becomes obvious. This elongation is not done in the meristem, but in another area further back.

ROOT HAIRS
Further back still, elongation has stopped and some of the root epidermal (skin) cells develop into single-celled structures called ROOT HAIRS. These are used to take in water and nutrients by intimate contact with the soil. Since they are extremely numerous, they have two effects:

• greatly increase the root surface area


• allow more intimate contact with soil - tending to bind fine, structureless soils

Root hairs are very short-lived and only occur close to the root tip. They are typically less than 1 cm (0.4 inches) in length.
STELE
The centre of the root forms the STELE, the specialised plumbing region. This consists of the XYLEM to carry water and nutrients upwards from the roots to the leaves, and the PHLOEM to carry manufactured food (sugars) from the leaves to the storage area (root) of the plant. Other processes, for example the distribution of growth substances, are also accommodated.