● There are types of tissues based on the types of `color{violet}("cells present.")`

● There are also tissues that vary depending on their location in the `color{violet}("plant body.")`

● Their `color{violet}("structure")` and `color{violet}("function")` would also be dependent on location.

● On the basis of their `color{violet}("structure")` and `color{violet}("location,")` there are three types of `color{violet}("tissue systems.")`

● These are:

`star` The `color{brown}( "epidermal")` tissue system,

`star` The `color{brown}("ground or fundamental")` tissue system

`star` The `color{brown}("vascular or conducting")` tissue system

● The `color{violet}("epidermal tissue system")` forms the outer-most covering of the whole `color{violet}("plant body")` and `color{violet}("comprises")` `color{brown}("epidermal cells, stomata")` and the `color{brown}("epidermal appendages")` – the trichomes and hairs.

`star` `color{green}("Epidermis:")`

● The `color{brown}("epidermis")` is the outermost layer of the `color{violet}("primary plant body").`

● It is made up of `color{violet}("elongated,")` compactly arranged `color{violet}("cells,")` which form a `color{violet}("continuous layer.")`

● Epidermis is usually `color{violet}("single layered.")`

● `color{violet}("Epidermal cells")` are `color{violet}("parenchymatous")` with a small amount of `color{violet}("cytoplasm")` lining the cell wall and a `color{violet}("large vacuole.")`

● The outside of the `color{violet}("epidermis")` is often covered with a waxy thick layer called the `color{brown}("cuticle")` which prevents the `color{violet}("loss of water.")`

● `color{violet}("Cuticle")` is absent in `color{violet}("roots.")`



`star` `color{green}("Stomatal Apparatus:")`

● `color{brown}("Stomata")` are `color{violet}("structures")` present in the `color{violet}("epidermis ")` of leaves.

● `color{violet}("Stomata")` regulate the process of `color{violet}("transpiration")` and `color{violet}("gaseous exchange.")`

● Each `color{violet}("stoma")` is composed of two `color{violet}("bean shaped cells")` known as `color{brown}("guard cells.")`

● In grasses, the `color{violet}("guard cells")` are `color{violet}("dumbbell shaped.")`



● The outer walls of `color{violet}("guard cells")` (away from the `color{brown}("stomatal pore")` ) are thin and the `color{violet}("inner walls")` (towards the stomatal pore) are highly thickened.

● The `color{violet}("guard cells")` possess `color{violet}("chloroplasts")` and `color{violet}("regulate ")` the opening and closing of `color{violet}("stomata.")`

● Sometimes, a few `color{violet}("epidermal cells,")` in the vicinity of the `color{violet}("guard cells")` become specialised in their `color{violet}("shape")` and `color{violet}("size ")` and are known as `color{brown}("subsidiary cells")`.

● The stomatal aperture, `color{violet}("guard cells")` and the surrounding `color{violet}("subsidiary cells")` are together called `color{brown}("stomatal apparatus")`

`star` `color{green}("Root Hairs and Trichomes:")`

● The `color{violet}("cells of epidermis bear")` a number of hairs.

● The `color{brown}("root hairs")` are `color{violet]("unicellular elongations")` of the `color{violet}("epidermal cells")` and help absorb water and minerals from the `color{violet}("soil.")`

● On the stem the `color{violet}("epidermal hairs")` are called `color{brown}("trichomes.")`

● The `color{violet}("trichomes")` in the `color{violet}("shoot system")` are usually multicellular.

● They may be branched or `color(violet}("unbranched")` and `color{violet}("soft or stiff.")`

● They may even be secretory.

● The `color{violet}("trichomes")` help in preventing `color{violet}("water loss")` due to transpiration.

● All `color{violet}("tissues except epidermis")` and vascular bundles constitute the `color{brown}("ground tissue.")`

● It consists of `color{violet}("simple tissues")` such as `color{violet}("parenchyma, collenchyma")` and `color{violet}("sclerenchyma. ")`

● `color{violet}("Parenchymatous cells")` are usually present in `color{violet}("cortex, pericycle, pith")` and `color{violet}("medullary rays,")` in the primary stems and roots.

● In leaves, the `color{violet}("ground tissue")` consists of `color{violet}("thin-walled chloroplast ") ` containing cells and is called `color{brown}("mesophyll.")`

● The `color{violet}("vascular system")` consists of `color{violet}("complex tissues,")` the `color{violet}("phloem")` and the `color{violet}("xylem.")`

● The `color{violet}("xylem")` and `color{violet}("phloem")` together constitute `color{violet}("vascular bundles.")`

● In `color{violet}("dicotyledonous")` stems, `color{brown}("cambium")` is present between `color{violet}("phloem")` and `color{violet}("xylem.")`

● Such `color{violet}("vascular bundles")` because of the presence of `color{violet}("cambium")` possess the ability to form `color{violet}("secondary xylem")` and `color{violet}("phloem tissues,")` and hence are called `color{brown}("open vascular bundles.")`

● In the `color{violet}("monocotyledons,")` the `color{violet}("vascular bundles")` have no `color{violet}("cambium ")` present in them.

● Hence, since they do not form `color{violet}("secondary tissues")` they are referred to as `color{brown}("closed.")`

● When `color{violet}("xylem")` and `color{violet}("phloem")` within a `color{violet}("vascular bundle ")` are arranged in an alternate manner on different radii, the arrangement is called `color{brown}("radial")` such as in `color{violet}("roots")`.

● In `color{brown}("conjoint")` type of `color{violet}("vascular bundles,")` the `color{violet}("xylem ")` and `color{violet}("phloem")` are situated at the same radius of `color{violet}("vascular bundles.")`

● Such `color{violet}("vascular bundles")` are common in `color{violet}("stems and leaves.")`

● The `color{violet}("conjoint vascular bundles")` usually have the `color{violet}("phloem")` located only on the outer side of `color{violet}("xylem.")`