Consists of four zones:

- The root cap

- Zone of cell division

- Zone of elongation

- Zone of differentiation/maturation

ANATOMY OF ROOT

ground meristem

procambium

Consists of parenchyma cells that cover the root tip.

The cells can be large or small, protecting the delicate or soft tissue behind it.

Cells on the surface of the root cap secrete a slimy substance called mucilage, which accumulates in the cell wall and finally released.

The Root Cap

Besides assisting the movement of root tip through the soil, the slimy mucilage provides a conducive environment for growth of useful bacteria.

Cells on the surface of the root cap which are eroded, are continuosly replaced from inside.

Zone of Cell Division  Consists of the apical meristem at the tip of root

The apical meristem forms three primary meristems:

a. Protoderm, that produces the epidermis on the outside

b. Ground meristem, the part internal to the protoderm which produces the parenchyma cells

of the cortex.

c. Procambium, a solid cylindrical structure in the middle of the root, which produces the primary

xylem and phloem.

Zone of Elongation

This zone is situated above the apical meristem. In

this region the cells are longer and broader than

their original shape.

At the same time, smaller vacuoles coalesce to

become one or two large vacuoles that occupy 90%

or more of the cell volume.

Only the root cap, the apical meristem and the

elongation zone that push the root deeper into the

soil. The region above the elongation zone is not

involved, since the cells within do not increase in

size anymore.

Other parts of the root do not move, unless there is

a cambium that will cause an increase in root size

through the formation of secondary tissues.

Zone of Differentiation/Maturation

In this region, the cells mature and differentiate into

different cell types. The change includes roor hair

formation through the elongation of the epidermal

cells.

Cuticle is formed on the root hairs and epidermal

cells to protect the cells from attack by bacteria,

fungal and other organisms, but at a thickness that

allows the absorption of water.

The cortex region

consists of parenchyma

cells which mostly store

food. To the inside is the

endodermis, consisting

of a single layer of

compact cells forming a

cylinder.

On the primary wall of the

endodemis, there is deposition of

suberin (a fatty substance) that

forms the casparian strips on the

radial and transverse walls.

The plasmalemma of endodermis

coalesce with the casparian strip

preventing movement of water,

except through plasmalemma

without casparian strips. Dangerous

heavy metals are prevented from

entering the cell while beneficial

ones are allowed in.

Equisetum endodermis with casparian strip

The endodermal cell may become thick due to

the deposition of suberin, wax, cellulose and

occasionally lignin.

To the inside of the endodermis is the vascular

cylinder (stele). In between the vascular

cylinder and the endodermis lies the pericycle

region, consisting of one layer of parenchyma

cells, or more layers in some plants.

Monocot root

Dicot root

Cells of the pericycle

continue to divide even

at maturity. Lateral

roots and part of the

vascular cambium of

dicot plants are formed

from the pericycle

tissue.

In most dicot and conifer roots, the primary xylem

consists of tracheids and vessels. The xylem forms

arms that radiate towards the pericycle, and there

can be two, three, four or more of such arms.

In monocot roots, and a few dicot roots, the primary

xylem encloses a central region of parenchyma cells,

which is the pith. The xylem arms are not very

prominent.

In the beginning, the cambium follows the shape

of the primary xylem arms during the formation

of secondary phloem on the outside and

secondary xylem on the inside. Finally, the

cambium position changes and the secondary

conductive tissue forms a cylinder.

Secondary growth in root

Primary phloems that are located in between two

primary xylem arms finally disappear when the

secondary tissue increases.

In roots of woody plants, a secondary cambium

which is the cork cambium (phellogen) is formed

from the pericycle to produce the cork tissue.