Dermal Tissue System (Outer Covering of Plant):
1) Epidermal Tissue (epidermis):
• Forms outermost layer
Cuticle: Waxy covering
• Reduces evaporation
• Inhibits microorganism invasion
Root Hairs: extended root surface
• Increase absorption
2) Peridermal Tissue (periderm):
• Only in woody plants (“bark = dead cells”)
• Protection; support
The epidermis can be
from one to several
cell layers thick.
It covers all the parts
of a plant; shoots,
stems, leaves, and
Layer of cells covering surface of entire
Acts as a barrier to fungi and other
microorganisms and pathogens.
Layer is thin and transparent.
Allow for light to pass through,
allowing for photosynthesis in the
Epidermal tissues have
abundant trichomes which are tiny
hairs projecting from surface of
Leaf trichomes trap water in the area
above the stomata and prevent water
Special Dermal Cells – Trichomes & Root hairs
– Hairlike outgrowths of
– Keep leaf surfaces cool and
• Roots hairs
– Tube extensions from
– Greatly increase the root’s
surface area for absorption
Root hairs are elongations of
epidermal cells in the root.
Root hairs maximise the
surface area over which
absorption of water from the
soil can occur.
Epidermal tissues in leaves are
covered with a waxy cuticle.
The waxy outer layer on the
epidermis prevents water
loss from leaves.
Epidermal tissues contain guard
cells containing chloroplasts.
Guard cells control the
opening and closing of the
pores known as stomata thus
controlling water loss in
Some plant epidermal cells can
secrete poisonous or bad-tasting
The bitter taste of the
substances deter browsing
and grazing by animals.
Epidermis continued: guard cells
Guard cells are bean shaped specialised
epidermal cells found mainly on the lower
surface of leaves which are responsible for
regulating the size of the stoma opening.
Together, the stoma and the guard cells are
referred to as stomata.
The stomata in the epidermis allow oxygen,
carbon dioxide and water vapour to enter and
leave the leaf.
The guard cells also contain chloroplasts for
-Only in woody plants (“bark = dead cells”)
Xylem has the dual function of
1. supporting the plant and
2. transporting water and dissolved mineral salts from
the roots to the stems and leaves.
-The vessels and tracheids are non-living at maturity and are hollow
to allow the transport of water
- Both vessels and tracheids have lignin in their secondary walls,
which provides additional strength and support.
-Tracheids have thick secondary cell walls and are tapered at the
-The thick walls of the tracheids provide support and tracheids do
not have end openings like the vessels.
-The tracheids' ends overlap with one another, with pairs of pits
present which allow water to pass through horizontally from cell to
2) Phloem (living at maturity)
A) Sieve Tubes: Wide, tube-like cells
B) Companion Cells: support and regulate sieve tubes
Phloem tissue is the living tissue responsible for transporting
organic nutrients produced during photosynthesis (mainly as
the carbohydrate) to all parts of the plant where these are
-The phloem tissue is made up of the following major types of
1. sieve elements: these are conducting cells which transport
2. parenchyma cells: which store food for transport in phloem.
3. companion cells: are associated with parenchyma cells and
control the activities of sieve tube elements, since the latter have
4. Fibres: unspecialised cells and
Nectar (flowers) from nectaries
Oils (peanuts, oranges, citrus) from accumulation
of glands and elaioplasts.
Resins (conifers) from resin canals
Macticifers (e.g., latex - milkweed, rubber plants,
Hydathodes (openings for secretion of water)
Digestive glands of carnivorous plants (enzymes)
Salt glands that shed salt (especial in plants
adapted to environments laden with salt).