Mature Tissues (Permanent Tissues)
In which growth has stopped completely or for a time. The cells may be living or dead, thin or thick walled.
Tissue types based on kind of constituent cells:
A. Simple
Homogenous, consisting of one kind of cells. e.g. parenchyma, collenchyma, sclerenchyma.
B. Complex
Heterogenous, consisting of more than one kind
of cells working together as a unit. e.g. xylem and phloem.
The Tissue Systems
All the tissues of a plant which perform the same general function form a tissue system.
There are four main tissue systems:
1. The dermal or epidermal tissue system.
2. The fundamental or ground tissue system.
3. The vascular tissue system.
4. The secretory and excretory tissue system.
The Dermal or Epidermal Tissue System
The dermal system forms the outer protective covering of the plant and is represented in the primary plant body by the epidermis. During secondary growth the epidermis may be replaced by another dermal system; the periderm forming the new protective tissue.
1. Epidermis (epi= upon, derma= skin).
Composition: Continuous single layer of cells except for certain small pores, called stomata and lenticels. In many plants it may be bi- or multiseriate.
In the case of roots the outermost layer is known as epiblema, piliferous layer or rhizodermis.
Origin: From protoderm or dermatogen of apical meristem.
Functions:-
• Protects the internal tissue from damage.
• Prevents evaporation of water.
• Serves in gas exchange.
• Plays a role in photosynthesis and secretion.
• Acts as store for water in Xyrophytic plants.
• Some develops into secretory tissues, stomata and absorbing hairs.
Shapes and Types of epidermal cells:-
2. Multiple epidermis Develpos from protoderm.
3. Hypodermis Develops from ground meristem.
4. Piliferous layer
In Monocot roots, called (epiblema or rhizodermis) from which absorbing root hairs arise.
5. Exodermis
Replaces the ruptured piliferous layer during secondary growth, with thick walled cells.
6. Periderm
During secondary growth in roots and stems, the epidermis replaced
by the periderm, with dead,
suberized cork cells forming new protective tissue.
7. Stomata• Openings in the epidermis, bounded by two guard cells.
• Subsidiary cells = 2 or more cells adjacent to guard cells and differ from other epidermal cells may be found or not.
• Stomatal opening + The guard cells = Stoma.
• Stomatal opening + The guard cells + subsidiary cells = Stomatal complex or stomatal apparatus.
• Found on the aerial parts of the plant.
Functions of stomata
• Gas exchange with aid of substomatal chamber.
• Water transpiration and evaporation.
Positions of guard cells
• Leveled:- At the same level of the epidermal cells.
• Sunken :- Blow the level of the epidermal cells.
• Sunken in chamber :- In grooves, covered with hairs.
Types of Stomata
A. Monocotyledonous Types
• Iris type • Gramineae type
No subsidiary cells. Two lateral subsidiary cells , one on each side.
• Palmae type • Canna type:-
Four subsidiary cells, two round & smaller. Four - six subsidiary cells.
B. Dicotyledonous Types
• Anomocytic (Ranunculaceous type) • Anisocytic (Cruciferous type)
No subsidiary cells. Three unequal subsidiary cells.
• Paracytic (Rubacious type) • Diacytic (Caryophyllaceous type)
Two or more subsidiary cells parallel Two subsidiary cells perpendicular
to the long axis of the pore. to the long axis of the pore.
8. Epidermal Appendages (Trichomes or Hairs)
Outgrowth of the epidermal cells, either covering (non-glandular) or glandular.
Functions of trichomes
• Control the rate of transpiration.
• Reduce the heating effect of sun light.
• Protect the plant against outer injurious effects.
Types of trichomes
I. Non-glandular (e-glandular)
A. Unicellular: Formed of one cell.
a. Papillose b. Unbranched c. Branched d. Stellate
B. Multicellular: Formed of more than one cell.
a. Unbranched (simple).
b. Branched
1. Simple-branched 2. Tree-like
Uniseriate body ending with two branches. Radiating unicellular hairs.
3. Peltate (scale hair) 4. Candelabra
Very short stalk ending with Uniseriate axis from which arise
plate-like structure. numerous unicellular branches of hairs.
II. Glandular
Has a swollen head formed of one or more secreting cells which may be:
A. Unicellular
(Pearl gland) with embedded foot and the head projecting outside.
B. Multicellular
a. Uniseriate stalk
1. Unicellular head 2. Multicellular head
One of the most interisting type of trichomes is Stinging hair
Contains poisonous liquid, consisting of basal bulb-like portion from which a stiff, slender, tapering , small knob-like point,when the animal or human body comes in contact with it , the sharp pointed end penetrates the skin and the fluid is transferred from the basal bulb to the body causing irritation.
الف شكر يا د: اسامة
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