On the basis of their structure and location, there are three types of tissue systems. These are the epidermal tissue system, the ground or fundamental tissue system and the vascular or conducting tissue system.
EPIDERMAL TISSUE SYSTEM
$\displaystyle \small \bullet$ It forms the outermost covering of whole plant body, which consists of epidermal cells, stomata, epidermal appendages (trichomes and hairs).
$\displaystyle \small \bullet$ It is made up of elongated, compactly arranged cells, which form a continuous layer. Epidermis is usually single layered.
$\displaystyle \small \bullet$ Epidermal cells are parenchymatous with a small amount of cytoplasm lining the cell wall and a large vacuole. The outside of the epidermis is often covered with a waxy thick layer called the cuticle which prevents the loss of water. Cuticle is absent in roots.
$\displaystyle \small \bullet$ Stomata are structures present in the epidermis of leaves. Stomata regulate the process of transpiration and gaseous exchange. Each stoma is composed of two bean shaped cells known as guard cells. In grasses, the guard cells are dumbbell shaped. The outer walls of guard cells are thin and the inner walls (towards the stomatal pore) are highly thickened. The guard cells possess chloroplasts and regulate the opening and closing of stomata. Sometimes, a few epidermal cells, in the vicinity of the guard cells become specialized in their shape and size and are known as subsidiary cells. The stomatal aperture, guard cells and the surrounding subsidiary cells are together called stomatal apparatus .
$\displaystyle \small \bullet$ The cells of epidermis bear a number of hairs. The root hairs are unicellular elongations of the epidermal cells and help absorb water and minerals from the soil. On the stem the epidermal hairs are called trichomes.
$\displaystyle \small \bullet$ The trichomes in the shoot system are usually multicellular. They may be branched or unbranched and soft or stiff. They may even be secretors. The trichomes help in preventing water loss due to transpiration.
THE GROUND TISSUE SYSTEM
$\displaystyle \small \bullet$ All tissues except epidermis and vascular bundles constitute the ground tissue.
$\displaystyle \small \bullet$ It consists of simple tissues such as parenchyma, collenchyma and sclerenchyma.
$\displaystyle \small \bullet$ Parenchymatous cells are usually present in cortex, pericycle, pith and medullary rays, in the primary stems and roots.
$\displaystyle \small \bullet$ In leaves, the ground tissue consists of thin-walled chloroplast containing cells and is called mesophyll.
VASCULAR TISSUE SYSTEM
$\displaystyle \small \bullet$ “The vascular bundle is defined as a strand of compactly arranged xylem and phloem tissues with or without cambium”.
$\displaystyle \small \bullet$ The xylem and phloem are the conducting vascular tissues, which are arranged in strand forms vascular bundles.
$\displaystyle \small \bullet$ Types of vascular bundles
Radial: In this vascular bundle the xylem and phloem are found in separate bundles, they are separated by non-vascular tissue. The xylem and phloem are alternate arrangement and equal in number. It is primitive vascular in which xylem and phloem occur in different radius. Ex: dicot root, monocot root.
Conjoint type: In this type of vascular bundle xylem and phloem are combined and occur in same radius. Types of conjoint vascular bundle
(i) Collateral
$\displaystyle \small \circ$ In a vascular bundle xylem and phloem remain together in side by side arrangement and they are occurring in same radius.
$\displaystyle \small \circ$ The xylem is towards inner side and phloem is towards outer side.
$\displaystyle \small \circ$ The collateral vascular bundle depends on presence or absence of cambium.
$\displaystyle \small \circ$ If the cambium is present between xylem and phloem it is called open type. Ex : dicot stem or sunflower stem.
$\displaystyle \small \circ$ In the collateral vascular bundle if cambium is absent it is called closed type. Ex : monocot stem.
(ii) Bicollateral
$\displaystyle \small \circ$ In this type of vascular bundle the phloem and cambium are in two sets and only one set of xylem.
$\displaystyle \small \circ$ They are always open type. Ex: stem of family apocyanaceae.
Concentric: In a vascular bundle if one vascular tissue is in the centre and another vascular tissue surrounded externally, it is called concentric vascular bundle. Types of concentric vascular bundle
(i) Amphicribal or Hadrocentric: In this type, xylem occur in centre and it is surrounded by phloem. Ex : ferns
(ii) Amphivasal or Laptocentric: In this type, the phloem occur in the centre and it is surrounded by the xylem. Ex : dracaena, yucca
EPIDERMAL TISSUE SYSTEM
$\displaystyle \small \bullet$ It forms the outermost covering of whole plant body, which consists of epidermal cells, stomata, epidermal appendages (trichomes and hairs).
$\displaystyle \small \bullet$ It is made up of elongated, compactly arranged cells, which form a continuous layer. Epidermis is usually single layered.
$\displaystyle \small \bullet$ Epidermal cells are parenchymatous with a small amount of cytoplasm lining the cell wall and a large vacuole. The outside of the epidermis is often covered with a waxy thick layer called the cuticle which prevents the loss of water. Cuticle is absent in roots.
$\displaystyle \small \bullet$ Stomata are structures present in the epidermis of leaves. Stomata regulate the process of transpiration and gaseous exchange. Each stoma is composed of two bean shaped cells known as guard cells. In grasses, the guard cells are dumbbell shaped. The outer walls of guard cells are thin and the inner walls (towards the stomatal pore) are highly thickened. The guard cells possess chloroplasts and regulate the opening and closing of stomata. Sometimes, a few epidermal cells, in the vicinity of the guard cells become specialized in their shape and size and are known as subsidiary cells. The stomatal aperture, guard cells and the surrounding subsidiary cells are together called stomatal apparatus .
$\displaystyle \small \bullet$ The cells of epidermis bear a number of hairs. The root hairs are unicellular elongations of the epidermal cells and help absorb water and minerals from the soil. On the stem the epidermal hairs are called trichomes.
$\displaystyle \small \bullet$ The trichomes in the shoot system are usually multicellular. They may be branched or unbranched and soft or stiff. They may even be secretors. The trichomes help in preventing water loss due to transpiration.
THE GROUND TISSUE SYSTEM
$\displaystyle \small \bullet$ All tissues except epidermis and vascular bundles constitute the ground tissue.
$\displaystyle \small \bullet$ It consists of simple tissues such as parenchyma, collenchyma and sclerenchyma.
$\displaystyle \small \bullet$ Parenchymatous cells are usually present in cortex, pericycle, pith and medullary rays, in the primary stems and roots.
$\displaystyle \small \bullet$ In leaves, the ground tissue consists of thin-walled chloroplast containing cells and is called mesophyll.
VASCULAR TISSUE SYSTEM
$\displaystyle \small \bullet$ “The vascular bundle is defined as a strand of compactly arranged xylem and phloem tissues with or without cambium”.
$\displaystyle \small \bullet$ The xylem and phloem are the conducting vascular tissues, which are arranged in strand forms vascular bundles.
$\displaystyle \small \bullet$ Types of vascular bundles
Radial: In this vascular bundle the xylem and phloem are found in separate bundles, they are separated by non-vascular tissue. The xylem and phloem are alternate arrangement and equal in number. It is primitive vascular in which xylem and phloem occur in different radius. Ex: dicot root, monocot root.
Conjoint type: In this type of vascular bundle xylem and phloem are combined and occur in same radius. Types of conjoint vascular bundle
(i) Collateral
$\displaystyle \small \circ$ In a vascular bundle xylem and phloem remain together in side by side arrangement and they are occurring in same radius.
$\displaystyle \small \circ$ The xylem is towards inner side and phloem is towards outer side.
$\displaystyle \small \circ$ The collateral vascular bundle depends on presence or absence of cambium.
$\displaystyle \small \circ$ If the cambium is present between xylem and phloem it is called open type. Ex : dicot stem or sunflower stem.
$\displaystyle \small \circ$ In the collateral vascular bundle if cambium is absent it is called closed type. Ex : monocot stem.
(ii) Bicollateral
$\displaystyle \small \circ$ In this type of vascular bundle the phloem and cambium are in two sets and only one set of xylem.
$\displaystyle \small \circ$ They are always open type. Ex: stem of family apocyanaceae.
Concentric: In a vascular bundle if one vascular tissue is in the centre and another vascular tissue surrounded externally, it is called concentric vascular bundle. Types of concentric vascular bundle
(i) Amphicribal or Hadrocentric: In this type, xylem occur in centre and it is surrounded by phloem. Ex : ferns
(ii) Amphivasal or Laptocentric: In this type, the phloem occur in the centre and it is surrounded by the xylem. Ex : dracaena, yucca
| Exarch | Endarch |
|---|---|
| Protoxylem is marginal | Protoxylem is central |
| Metaxylem is central | Metaxylem is marginal |
| Cenripetal development | Centrifugal development |
| Found in roots | Found in stem |
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