1 plant anatomy dr. wael m. ibrahim botany department faculty of science fayoum university 2 nd year...

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PLANT ANATOMY

Dr. Wael M. Ibrahim

BOTANY DEPARTMENTFACULTY OF SCIENCE

Fayoum UNIVERSITY

2nd year

Biology Students

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ContentsDuring first year

I- Plant cell A- Protoplasmic components (Cytoplasm & Organelles). B- Non protoplasmic comp. (Vacuole & Ergastic subst.). C- Cell wall.

II- Plant tissues A- Meristematic tissues. B- Mature (Permanent) tissues: 1- Dermal system (Epidermis). 2- Ground system (Parenchyma & Collenchyma). 3- Vascular system (Xylem & Phloem).

III- Plant organs A- Primary structures (Young root, stem & leaf)

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During second year

I- Plant tissues - Mature (Permanent) tissues: 1- Dermal system (Periderm, Bark, Lenticels). 2- Vascular system (stele & vascular bundles).

II- Plant organs - Secondary thickening 1- Normal Secondary thickening 2- Abnormal Secondary thickening

III- Ecological anatomy A- Hydrophytes. B- Xerophytes.

Contents

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Mature (Permanent) tissues A- Dermal tissue system

- These are outer protective tissues which develop in

stems and roots, mostly to replace the epidermis which

has been ruptured due to the increase in diameter of the

organs by the secondary growth.

Usually Monocot. do not form periderm as in dicot.

- These structures include :

a- Periderm (or Cork),

b- Bark,

c- Lenticels and

d- Abscission zone..

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Mature (Permanent) tissues

A- Dermal tissue systema- Periderm (or Cork)

- Periderm is an outer impermeable protective tissue which is generally formed durind secondary growth in stems and

roots, In certain cases the formation of periderm is not related to

secondary growth, e.g. potato tubers (underground stem) it is formed for protection against attacks by soil organisms prevent dessiccation cover wounds which formed by leaf or fruit fall or branches of trees break. - Periderm is composed of three layers : (2) Phellem or cork to outside. (1) Phellogen or cork cambium which produces. (3) Phelloderm or 2ry ground tissue to inside.

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Mature (Permanent) tissues

A- Dermal tissue system

(i) Phellogen or cork cambium: - It is a secondary lateral meristem arises from the

permaent living celles of the epidermis hypodermis cortex phloem pericycle of roots - The phellogen may form a complete layer or isolated

patches. In ridged stems the phellogen below the ridges is

slightly deeper than below the grooves.

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- Phellogen is composed of one layer of meristematic cells

with the same shape and size,

appear in T.S. rectangular and radially flattened.

- Phellogen cells divided to two cells

one to the outside which is gradually change into phellem (cork)

one to the inside which gradually chage to the parenchymatous form to give the phelloderm.

So the phellogen activity adds to the diameter of the stem or the root.

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(ii) Phellem or cork:

- These are layers formed towards the outside of the plant organ.

- At the early stages of their formation cork cells are compactly arranged and have thin cellulosic cell walls.

- As they mature cells elongate and lay down suberin on their celulosic cell wall and gradually loss their living materials (i.e. become dead cells)

- Dead cork cells may contain resins or tannins in their lumen which give a brown or a yellow colour to cork; however the lumen may be filled with air (very light cork).

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(iii) Phelloderm or 2ry ground tissue:

- These are layers of thin walled cells produced toward the inner side of the phellogen.

- These are living cells with thin cellulosic walls

In some species they may contain chloroplasts and starch.

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b- Bark (Rhytidome):

- Cork formation results in the isolation of the outer tissues of the plant organ. They loss thier water and nutrients. Consequently they soon dry up, die and fall down.

-Rhytidome is a term used to define all tissues present outside the phellogen (not separate from the plant) -however, the term bark is more specifically used to designate the tissues that separate from the plant axis as a result of phellogen activity.

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Mature (Permanent) tissues 36

A- Dermal tissue system 36

- There are two types of bark scale bark and ring bark

(a) Scale bark is produced when the periderm arises in separated layers, where the outer tissues break up into units related to the underneath periderm.

The separated dead tissues as well as the attached cork layers are termed scalebark, e.g. Pinus stem.

(b) Ringbark is formed when complete phellogen rings arise around the entire circumferance of the axis.

An annular ring or hollow cylinders of tissues are separated from the axis.

Ringbark is formed only in species in which the 1ry phellogen appears in relatively deep layers of cells, e.g. Vitis stem.

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c- Lenticels: - They are small areas, in the periderm, of loose

cells with abundant intercellular spaces

- Functionally lenticels replaces stomata for gaseous exchange, after the destruction of stomata and epidermis during secondary growth & cork formation.

- Lenticels originate, usually beneath stomata, at an early stage of cork formation.

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The phellogen cells below a stoma divide to produce,instead of cork cells, a mass of rounded thin walled celles with intercellular spaces, which lose their protoplast and become colourless (dead) known as the complementary tissue.

During winter, in some plants, the lenticel phellogen divides to close the lenticel by producing another type of suberized cells below the complementary tissue known as the closing layers.

In spring rapid development of new complementary tissue breaks open the closing layers.

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d- Abscission zone (Leaf abscission): - In angiosperms and gymnosperms leaves fall

down before the plants die. - This abscission zone protected the living tissues

in the stem from desiccation and infection.

-The abscission zone consists of two layers:

(i) An abscission or separation layer towards the leaf blade

(ii) A protective layer towards the leaf base.

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- Leaf abscission starts by the dissolution of the middle lamellae or the entire cells, or the accumulation of liquid in the intercellular spaces of the abscission layer, only in the cells surrounding the vascular region.

At that time the leaf is only held by the vascular region.

- The formation of tyloses (balloon-like outgrowthes from the walls) in the xylem vessles stop water supply to the leaf.

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Alittle disturbance of the leaf by wind or any other

mechanical pressure (& the weight of the leaf itself) cause the break of the vascular tissue and the leaf falls.

- Shortly after the leaf fall the protective layers develop on the exposed surface. The cells of the protective layers deposite lignin and suberin on their walls and in the intercellular spaces.

This protective layer is soon replaced by periderm which develops below the protective layer.

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1 plant anatomy dr. wael m. ibrahim botany department faculty of science fayoum university 2 nd year...

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