2. LEAF
• Leaves are the thin and flat lateral outgrowths from
stem nodes.
• They are the main vegetative organs of a plant body,
concerned with photosynthesis, transpiration and gas
exchange.
• Leaves are produced from a superficial meristematic
tissue, called leaf primordia and hence they are
exogenous in origin.
• The part of the stem that bears leaf is called the
node.
• Each leaf possesses an axillary bud at its axil.
3. • In many cases, the same plant bears different kinds of leaves.
• This condition is known as heterophylly.
• It is quite common among hydrophytes (e.g.. Limnophila
heterophylla).
• Here, the submerged part of the shoot bears dissected leaves
and the aerial part bears entire leaves.
• Some terrestrial plants may also have two types of leaves
(e.g., coriander)
• Leaves show great variations in size, form, outline, surface
texture, etc.
• In size, they vary from minute scales to the exceptionally large
leaves of certain palms, which are sometimes 40 feet long.
• In form, some leaves are more or less circular, some others
are long and narrow, but most leaves are of intermediate
shape.
6. Parts of a Dicot leaf
• A typical dicot leaf has three parts, namely
• Leaf base or Hypopodium
• Leaf stalk or Mesopodium
• Leaf lamina or Epipodium.
7. (a) Leaf base
• Leaf base is the initial part of a leaf that attaches to the
stem.
• The upper angle between the leaf base and the stem is
called axil.
• In some plants (e.g., Leguminosae), leaf base is swollen
and is called pulvinus.
• Leaves with pulvinus are called pulvinate leaves (e.g.,
Mimosa pudica, Mangifera indica).
• Pulvinus is responsible for the sleep movement of
leaves (nyctinasty) in Mimosa.
• In monocot leaves, leaf base has a sheath-like
expansion, called sheathing leaf base (e.g., banana,
grasses).
• It partially or completely encircles the stem.
8. • In many dicots, a pair of leafy lateral outgrowths are
given out from the leaf base. They are called stipules.
• Stipules usually protect the developing buds.
• Leaves with stipules are called stipulate leaves (e.g.,
Hibiscus, Ixora), and
• those without stipules are called exstipulate leaves
(e.g., Mangifera).
• Stipules are believed to protect the developing
embryonic leaf.
• Occasionally, they may get modified to enclose the leaf
bud (e.g., Ficus).
11. (b) Leaf stalk
• Leaf stalk is the slender middle part that connects
the lamina with the base.
• The stalk of a simple leaf is called petiole, and that
of a compound leaf is called rachis.
• In some cases, leaves are without stalk and they are
called sessile leaves (e.g., Calotropis, Zinnia).
• A leaf having petiole is called petiolate leaf (e.g.,
Hibiscus, Ficus).
• In some plants, petiole is wing-shaped (e.g., Citrus).
12. (e) Leaf lamina
• Lamina, or leaf blade, is the green, thin and expanded part of
the leaf.
• It is actively involved in photosynthesis, respiration and
transpiration.
• Its tip is called leaf apex, and the edge or border is called leaf
margin.
• Petiole extends throughout the length of the lamina as a
strong vein, called mid-vein or mid-rib.
• Mid-rib gives our bilateral branches to both sides. They are
called veins.
• Veins, in turn, irregularly branch and re-branch into veinlets.
• Mid-rib, veins and veinlets form a network which constitutes
the structural frame work of the leaf lamina
13. • Also serves as the vascular strands or channels for
the transport of organic food, water and minerals.
• Apex and margin of the lamina are variously
shaped.
• Leaf margin is entire and smooth in some cases.
(e.g. banana, grasses).
• In some others, it is toothed or serrated. (e.g.
Hibiscus.)
• In yet others, it is lobed (e.g. tapioca), or wavy and
uneven (e.g. Polyalthia)
• Leaf surface is smooth or curved, with a waxy
coating.
• In some cases, it may bear hairs.
17. Monocot leaf
• Monocot leaf is similar to dicot leaf in its basic morphology.
• It also has the three parts leaf base, petiole and lamina.
• Leaf base is sheathing in monocots.
• It partially on completely encircles the stem.
• Petiole is absent in grasses.
• In some palms, it is modified into a rachis.
• In some monocots, there is a pair of small outgrowths from
the junction between the leaf base and petiole.
• They are called ligules (e.g., grasses)
• The lamina of monocot leaves is isobilateral (lower and
upper sides similar )
• Venation is parallel in monocot leaves.
19. Venation
• Venation is the pattern of arrangement of veins in the leaf blade.
• There are two kinds of venation, namely reticulate venation and
parallel venation .
• In reticulate venation the veins and veinlets form an anastomosing
network
• In parallel venation veins are parallel to one another.
• Parallel venation is horizontal in some cases (e.g. banana), and
longitudinal in others (e.g. bamboo and other grasses, lilies).
• Reticulate venation is characteristic of dicot leaves, and parallel
venation is characteristic of monocot leaves.
• However, there are exceptions. For example, dicots, such
Calophyllum, Alstonia and Eryngium, show parallel venation, and
monocots, such as aroids, Dioscorea (climbing yam), etc. show
reticulate venation.
20.
21. Kinds of leaves
• Based on the number of lamina, or the nature of
the incision of lamina, two kinds of leaves can be
recognized,
•Simple leaves
•Compound leaves
22. (a) Simple leaves
• These are the leaves with only a single lamina
(e.g., Hibiscus).
• In this case, the lamina is entire or incised, but
the incision does not touch the mid-rib nor
does it reach the tip of the petiole.
23.
24. (b) Compound leaves
• These are the leaves whose lamina is divided into
segments, called leaflets or pinnae.
• Unlike leaves, leaflets are devoid of buds or stipules in
their axils.
• Individual leaflets may be stalked or sessile, and free
from each other.
• At the same time, all of them are connected to a
common stalk, called rachis.
• A compound leaf resembles a branch, and each leaflet
of it resembles a simple leaf.
• Yet, a compound leaf differs from a branch in the
absence of terminal and axillary buds and in its
development from a node; a branch develops from the
axillary bud of a leaf.
25.
26. Types of compound leaves
• There are two types of compound leaves, namely
•Pinnately compound
•Palmately compound.
27. 1. Pinnately compound leaves
• These are the compound leaves in which leaflets
are arranged biserially in two ranks on both the
sides of the rachis.
• This is similar to the arrangement of the pinna or, of
a bird's feather. e.g., Neem (Azadirachta indica),
Moringa.
• There are 4 type of pinnately compound leaves.
• They are unipinnate, bipinnate, tripinnate and
decompound leaves.
28. (1) Unipinnate or simple pinnate leaves
• These are the pinnately compound leaves in which the
rachis bears leaflets in opposite or sub-opposite pairs.
• There are two types of unipinnate leaves
• They are paripinnate and imparipinnate.
• In paripinnate leaves, leaflets are paired and hence
even-numbered and the rachis ends in a pair of them
e.g. Tamarindus, Vicia
• In imparipinnate leaves, leaflets are odd-numbered and
the rachis ends in a single leaflet. e.g., rose, neem,
Murraya.
29.
30. (ii) Bipinnate leaves
• These are the pinnately compound leaves in which
the primary rachis beans secondary axes, called
rachillae, which bear leaflets on both the sides.
• So, the leaves pinnate twice.
• e.g. Acacia, Mimosa pudica.
31.
32.
33. (iii) Tripinnate leaves
• These are the pinnately compound leaves in which
the primary rachis gives out secondary rachi which,
in turn, give out tertiary rachi to which leaflets are
attached, So, the leaves pinnate thrice
• e.g. Moringa.
34.
35. (iv) Decompound leaves
• These are the 2 types Pinnately compound leaves
and Palmately compound leaves
1. Pinnately compound leaves
• Pinnately compound leaves in which the tertiary
rachi undergo further branching so that the leaves
pinnate more than thrice.
• e.g. Coriander.
36. 2. Palmately compound leaves
• Palmately compound leaves are the leaves in which
leaflets radiate from the tip of the rachis, just like
the fingers on palm.
• They are of five kinds, namely
1. Unifoliate
2. Bifoliate
3. Trifoliate
4. Quadrifoliate
5. Multifoliate.
37. Unifoliate leaves are the palmately
compound leaves with only a single
leaflet e.g. Citrus.
41. Multifoliate or digitate leaves have
more than four terminal leaflets. e.g.
Bombax (silk cotton), tapioca.
42.
43.
44. Differences between compound
leaves and branches
Compound leaf Branch
Not divided into nodes and
internodes
Divided into nodes and internodes
Axillary buds are absent in the
axils of leaflets
Axillary buds are present in the axils
of leaves
Terminal bud is absent Terminal bud is present
Bears leaflets on a branching rachis Bears leaves at nodes
Will not bear flowers and fruits Will bear flowers and fruits
