6 -Epidermis

It occurs on the surface of plants It occurs on the surface of plants and it is a complex tissue and it is a complex tissue

consisting of consisting of epidermal cellsepidermal cells, , stomatastomata and and trichomestrichomes (hairs) (hairs)..

Function of epidermis:

1 -Protect the plant from water loss in transpiration.

2 -It acts as boundary tissue surrounding the plant.

3 -Exchange of gases through the stomata.

4 -Storage of water and metabolic products.

1 -Epidermal cells

ShapeShape:: tabular in tabular in side view, side view,

isodiametric or isodiametric or elongated in elongated in surface viewsurface view..

Cell wallCell wall:: straight, wavy straight, wavy

wallswalls..

CuticleCuticle:: epidermal cells are covered by epidermal cells are covered by an impermeable layer known as cuticle an impermeable layer known as cuticle

which varies in thickness. The cuticle which varies in thickness. The cuticle may be smooth as in Stramonium or may be smooth as in Stramonium or

striated as in Belladonnastriated as in Belladonna..

The cuticle is formed mainly of cutin The cuticle is formed mainly of cutin which is an aggregate of modified fatty which is an aggregate of modified fatty

acids, partly combined with alcoholsacids, partly combined with alcohols..

2 -Stomata These are openings in the epidermis of These are openings in the epidermis of

stem and leaves. They occur in both stem and leaves. They occur in both surfaces or only on lower surface. In surfaces or only on lower surface. In

water plants they occur in upper water plants they occur in upper surfacesurface..

Types of stomataTypes of stomata:: The types are indicated either with The types are indicated either with

regard to the characters of the regard to the characters of the guard guard cellscells or with regard to the or with regard to the epidermal epidermal

cells surrounding the stomatacells surrounding the stomata..

Types according to the characters and arrangement of surrounding cells (subsidiary

cells)11 - -Ranunculaceous or Ranunculaceous or

Anomocytic stomata Anomocytic stomata (irregular celled):(irregular celled): The The

surrounding cells surrounding cells (subsidiary cells) are of (subsidiary cells) are of

varying number have no varying number have no special arrangement special arrangement and generally do not and generally do not

differ from other differ from other epidermal cells e.g. epidermal cells e.g.

DigitalisDigitalis..

22 - -Rubiaceous or Rubiaceous or Paracytic (parallel Paracytic (parallel

celled):celled): the stoma is the stoma is surrounded by two surrounded by two or more subsidiary or more subsidiary cells, two of which cells, two of which

have their long axes have their long axes parallel to the parallel to the

osteole e.g. Sennaosteole e.g. Senna..

33--Caryophyllaceous or Caryophyllaceous or Diacytic (cross Diacytic (cross

celled):celled): the stoma is the stoma is surrounded by surrounded by

subsidiary cells subsidiary cells having their long having their long

axes perpendicular to axes perpendicular to the osteole e.g. the osteole e.g.

MenthaMentha..

44 - -Cruciferous or Cruciferous or Anisocytic (unequal Anisocytic (unequal celled):celled): the stoma is the stoma is

surrounded by surrounded by usually three or usually three or

more subsidiary more subsidiary cells one of which is cells one of which is

distinctly smaller distinctly smaller than the others e.g. than the others e.g.

BelladonnaBelladonna..

3 -Trichomes (Hairs)

Epidermal cells are sometimes extended Epidermal cells are sometimes extended outwards forming projections of variable outwards forming projections of variable

shape and size. If it is short and conical it is shape and size. If it is short and conical it is called called papillaepapillae and the epidermis is and the epidermis is

described as papillosed e.g. Coca, but if the described as papillosed e.g. Coca, but if the projections are long and well protruding projections are long and well protruding

they form they form trichomestrichomes or hairs or hairs..

The part of The part of trichome trichome embedded in embedded in the epidermis is called foot while the epidermis is called foot while

the free part is the body. Hairs are the free part is the body. Hairs are classified into glandular and non-classified into glandular and non-

glandular or covering hairsglandular or covering hairs..

Non-glandular hairsNon-glandular hairs

UnicellularUnicellular MulticellularMulticellular

UnbranchedUnbranched BranchedBranched UnbranchedUnbranched BranchedBranched

11 - -CottonyCottony22 - -CystolithCystolith

33 - -e.g. Sennae.g. Senna

11 - -SimpleSimple22 - -StellateStellate

33 - -PeltatePeltate44 - -CandelabraCandelabra

11 - -UniseriateUniseriate22 - -BiseriateBiseriate

33 - -PluriseriatePluriseriate

A- Covering trichomes or non-glandular hairs

I- Unicellular:I- Unicellular: formed of one formed of one

cellcella- Unbrancheda- Unbranched or or

simple: e.g. simple: e.g. cottony hair, cottony hair,

cystolitic haircystolitic hairb- Branched:b- Branched: e.g. e.g.

LavenderLavender..

II- Multicellular:II- Multicellular: that that is formed of more is formed of more

than one cellthan one cell

a- Unbrancheda- Unbranched or or simplesimple::

11 - -Uniseriate:Uniseriate: formed of one row formed of one row as in Belladonna, as in Belladonna,

stramoniumstramonium. .

22 - -Biseriate:Biseriate: formed formed of two rows, each of two rows, each

row of one (twin row of one (twin cell) as in Arnica cell) as in Arnica

flower, or more flower, or more cells as in cells as in CalendulaCalendula..

33 - -Pluriseriate:Pluriseriate: formed formed of many rows of cells of many rows of cells

(Shaggy hair) as in (Shaggy hair) as in CuminCumin..

b- Branchedb- Branched::

11 - -Simple branched:Simple branched: with uniseriate body with uniseriate body

ending in two ending in two branches e.g. branches e.g.

TobaccoTobacco..

22 - -Stellate:Stellate: radiating radiating

unicellular unicellular hairs e.g. hairs e.g. KarkadehKarkadeh..

33 - -Peltate:Peltate: with very with very short axis short axis

surmounted by a surmounted by a plate-like plate-like

structure of structure of closely joined closely joined cells e.g. Oleacells e.g. Olea..

44 - -Candelabra:Candelabra: having uniseriate having uniseriate

axis from which axis from which arise numerous arise numerous

unicellular unicellular branches of hairs branches of hairs

e.g. Verbascume.g. Verbascum..

B- Glandular hairs I- Unicelluar:I- Unicelluar: not of common occurance, not of common occurance,

present in Piperpresent in Piper..

II- Multicellulr:II- Multicellulr: the most common type. They the most common type. They consist of several cells and are classified consist of several cells and are classified

intointo::

A- Unicellular stalkA- Unicellular stalk::andand;;* * Unicellular head Unicellular head

e.g. Menthae.g. Mentha..* * Bicellular head e.g. Bicellular head e.g.

DigitalisDigitalis..* * Multicellular head Multicellular head

e.g. Labiaceous hair e.g. Labiaceous hair in Mentha and in Mentha and clavate hair in clavate hair in

BelladonnaBelladonna..

B- Multicellular B- Multicellular stalkstalk::

a- Uniseriate stalk a- Uniseriate stalk e.g. Belladonnae.g. Belladonna..

b- Biseriate stalkb- Biseriate stalk and biseriate and biseriate

head or head or compositae compositae

type e.g. type e.g. ChamomileChamomile..

c-c- Pluriseriate Pluriseriate stalkstalk and a and a

head with head with numerous numerous

mostly eight mostly eight radiating cells radiating cells e.g. Cannabise.g. Cannabis..

d-d- Branched Branched stalk:stalk: the the

branch ending branch ending in head as in in head as in Hyoscyamus Hyoscyamus

muticusmuticus..