Describes about a leaf, it's parts, modifications and it's functions.

1. The
LEAF
By: Joel.R

2. What is a leaf?
The lateral flat, thin green, broad
outgrowth arising from the node is known
as leaf

3. Why are the
leaves green?
The Leaves are
green because
of the presence
of chlorophyll.

4. Parts of a leaf
1: Lamina or leaf Blade- It is the green flat and broad part
of the leaf. It is well adapted to absorb sunlight and carbon
dioxide for photosynthesis.
2: Leaf base- It is the part of leaf in contact with the node.
3:Petiole or leaf stalk-It is the stalk by which the leaf
lamina is attached to the main stem.
4:Midrib: The petiole enters into the lamina of the leaf and
continues as the Midrib
5: Veins: Midrib gives out numerous fine branches called
Veins
6: Veinlets: The veins Divide and subdivide to form a
network of Veinlets which keep the leaf expanded form
7: Leaf apex: The tip of the lamina is called the leaf apex
8:Leaf margin: The edge on all sides is called Leaf Margin

5. Types of leaves
Simple leaves Compound leaves

6. Simple leaves
The leaves in which the
lamina is undivided is a
single piece are called
simple leaves. In these
leaves, various margin
incisions, if present, never
touch the midrib

7. Compound leaves
The leaves in which the lamina is
divided into small segments
which are attached to the midrib
(rachis) and its branches or tip of
of the petiole are called
compound leaves. In these,
leaves incisions reach up to the
midrib or the petiole .

8. Venation
The arrangement of veins and veinlets in a
leaf is known as venation. It is of two types:
(i)Reticulate venation
(ii)Parallel venation

9. Reticulate venation
When the veins and
veinlets are irregularly
distributed in the lamina of
the leaf forming a network,
it is known as reticulate
venation.example- Peepal
and Mango

10. Parallel venation
When veins and
veinlets run parallel
to each other
towards the tip of
the leaf it is known
as parallel venation

11. Phyllotaxy
The arrangement of leaves on the
stem is called Phyllotaxy. It prevents
overcrowding of leaves and helps in
better exposure of leaf to sunlight and
air

12. Types of phyllotaxy
Opposite phyllotaxy Alternate phyllotaxy
Whorled Phyllotaxy

13. Opposite phyllotaxy
If two leaves are borne
one on either side of the
same node, the
phyllotaxy is said to be
opposite. e.g., Tulsi,
jasmine, guava.

14. Alternate phyllotaxy
If the single leaf is born
alternately, one at each
node, it is called
alternate phyllotaxy.
e.g., Rose, castor,
peepal, china rose,
sunflower.

15. Whorled Phyllotaxy
If three or more leaves
are borne at each node,
the arrangement is
called whorled. e.g.,
Kaner, oleander
(Nerium).

16. FUNCTIONS OF LEAF
(i ) Photosynthesis : The process by which green plants prepare their food with the
help of carbon dioxide and water in the presence of sunlight and chlorophyll is
known as photosynthesis.
(ii ) Exchange of gases : Stomata present in the leaves help in the exchange of gases
for photosynthesis and respiration.
(iii ) Transpiration : The removal of excess of water from the plants in the form of
water vapours through stomata is called transpiration.
(iv) Reproduction : In some plants, leaves have buds and these buds produce new
plants. e.g., Bryophyllum.
(v) Storage : The leaves of some plants become fleshy to store food. e.g., Onion.

17. MODIFICATION OF LEAVES
Along with the important vital function
of leaf, i.e., photosynthesis, leaves of
certain plants get modified to perform
some additional functions to cope up
with the needs of environment. It is of
following types :

18. (i ) Leaf tendril : In some weak stemmed plants, either the
whole leaf or leaflet or some other parts may be modified
into tendril. In sweet pea plant, the terminal leaflets are
modified into tendril to climb a support or to expose their
leaves to sunlight. e.g., Pea and Lathyrus (whole leaf),
Gloriosa (leaf tip), Smilax (stipular tendril).

19. (ii) Spines : The leaves are modified to hard
pointed spines to reduce water loss. They
also protect the plant from grazing animals.
e.g., Asparagus, opuntia (cactus), prickly
pear etc.

20. (iii ) Phyllode : In Australian acacia, a very much
divided lamina falls off to reduce transpiration. The
petiole then becomes expanded into a green, flat,
leaf-like photosynthetic structure. It is called
the phyllode. It helps in conservation of water and
reducing water loss.

21. (iv) Hooks : In Bignonia, terminal leaflets
become modified into hooks for climbing on
the support. The hooks give the appearance
of the claws of a cat.

22. (v) Scale leaves : These are dry, brown,
membranous, non-photosynthetic leaves which
take a protective role and are present on nodes
of aerial stem (e.g., Ruscus, Asparagus) or
underground stem (e.g., Ginger).

23. (vi ) Pitcher plant : In Nepenthes khasiana, lamina becomes modified into a
pitcher to capture insects for supplementing nitrogen supply. The leaf tip
forms the lid and the petiole becomes a long, thin, coiled structure supporting
the pitcher. Along the edges of the opening of the pitcher are placed small
hooks. An insect is trapped in the pitcher and digested by the secretion of
enzymes into the sac. The slender structure at its lower end is a modified leaf
base. The leaf base is green, flattened and photosynthetic.

24. (vii) Bladder : In Utricularia, some of the leaf
segments become modified to form a sac-like
bladder leaving a small aperture. The insects
enter through this opening and are digested
by the secretion of enzymes

25. (viii) Venus flytrap : In case of Venus flytrap, leaf
blade is divided into two parts, hinged along the
midrib. The two parts get interlocked by
marginal teeth and prevent the insect from
escaping. e.g., Venus flytrap.

26. VEGETATIVE PROPAGATION IN LEAF
In some plants, leaves are modified to bear
foliar buds from which new plants grow
and develop e.g., Bryophyllum (Sprout-leaf
plant) and Begonia (Elephant-ear plant)

27. • The leaf in Bryophyllm plant is broad and
has notches at its margin.
• Buds arise from the notches. These Buds
are called Epiphyllous buds
• When the buds drop off from the leaves
and paced in soil, they develop into new
plants with roots and small leaves. The
vegetative propagation in Begonia is also
in the similar way.

28. Thanks for your attention