Ground Tissue System
It is also called the fundamental tissue system. This tissue system constitutes the main bulk of the body of plants. The tissues that do not come under the epidermal tissue system and vascular tissue system constitute the fundamental or ground tissue system. Various simple tissues like parenchyma, collenchyma and sclerenchyma are present in it.
The ground tissue system is clearly differentiated into various zones. In the transverse section of all dicot stems, monocot roots and dicot roots; the ground tissue exhibits clear zonation into an outer cortex and central pith. In between cortex and pith various other tissues are present which will be discussed later in anatomy of stems and roots. Such differentiation is not present in the monocot stems. In the leaves of monocot and dicot plants, ground tissue is called mesophyll and is not distinguished into cortex and pith.
Zonation in Ground Tissue System: In dicot stems and all roots of angiosperms, following zonation is usually seen from outer to inner side in a transverse and longitudinal view.
(a) Cortex: It lies below the epidermis. It may be few to many layered in thickness. It is further diferentiated into three sub-zones, i.e., hypodermis, general cortex and endodermis.
Cortex: It lies below the epidermis. It may be few to many layered in thickness. It is further differentiated into three sub-zones, i.e., hypodermis, general cortex and endodermis.
Hypodermis: This is the outermost portion of cortex in stems of flowering plants. Hypodermis is absent in roots. It may be single to multilayered. The dicotyledonous stems have collenchymatous Hypodermis, i.e., made up of collenchymatous cells and the monocotyledonous stems have Sclerenchymatous hypodermis, i.e., made up of sclerenchymatous cells. Hypodermis is protective in function. Its cells may have chloroplasts in them and thus, may perform photosynthesis also.
General cortex: Next to hypodermis in stems and to epidermis in roots, lies the general cortex
It is few to many layered in thickness. It is parenchymatous in both stems and roots. The cells
Are thin-walled and may or may not have the intercellular spaces between them. The cells of cortex of young stems and leaves possess chloroplasts and perform photosynthesis. General cortex provides the mechanical support, performs photosynthesis in leaves and young stems and also stores the food material.
(ii) Endodermis: The innermost layer of cortex is called endodermis. All the tissues on the inner side of the endodermis constitute the stele which comprises pericycle, vascular bundles and pith. Hence endodermis is the border between the general cortex and the stele.
Endodermis is a single layer of compactly arranged cells. The cells constituting this layer are elongated with their long axis parallel to the longitudinal axis of plants.
In transverse section (T.S.), the cells of endodermis appear barrel-shaped (drum or large
Cylinder shaped) or oval shaped.
The cells constituting endodermis are living and may contain starch grains. This is the reason
That endodermis is also called the starch sheath.
Casparian strips: Endodermis is characterised by the presence of a special thickened’ band in their wal
Called casparian strip. This thickening was first observed by Caspary, hence the name. This thickening
Appears on the radial as well as on the tangential walls of endodermal cells. This band-like structure is
Generally formed by the deposition of a water-impermeable waxy material suberin. Hence, walls of
Endodermal cells are suberized. Due to presence of casparian strips, the endodermis is impervious to water.
A distinct endodermis is a constant feature of roots of all plants but in stems it is not very distinct.
- Pericycle : It is the outermost portion of stele. It is a cylinder of thin-walled parenchymatous or
Sometimes thick-walled sclerenchymatous tissue. It may be single-layered to multilayered. The cells
May be thin-walled to thick-walled. Pericycle may be present in the form of patches also. Pericycle is
Not present in monocotyledonous stems.
Functions of pericycle:
0 Thick-walled pericycle gives mechanical support to the plants.
When composed of parenchymatous cells, it may act as storage organ of food materials.
(il) In dicot roots, the pericycle becomes meristematic and forms a part of the cambial ring. This
Cambial ring gives rise to the secondary tissues.
Pericycle gives rise to the lateral roots.
© Pith: It is also called medulla. It occupies the central part in dicot stems, dicot roots and monocot
Roots. In monocot stems, pith cannot be distinguished as vascular bundles are present through out the
Stem. Pith is generally composed of large parenchymatous cells with intercellular spaces present
Between them. Sometimes sclerenchymatous cells are also present in pith. E.g., Compositae.
Pith rays or medullary rays: These are the extensions of pith. In most dicotyledons, the peripheral
Layers of pith extend between the vascular bundles and are in contact with the pericycle. These
Extensions appear like rays and thus, they are called the pith rays. The pith rays are also called the
Ground tissue in leaves
The ground tissue is not differentiated into cortex and pith in the leaves. Ground tissue consists of thin-walled
Chloroplast containing cells and is called mesophyll.