This document provides information on the structure, adaptations, and development of leaves. It describes the key characteristics and parts of leaves including the lamina, petiole, stipules, venation patterns, and modifications. The functions of leaves are explained as photosynthesis, transpiration, conduction of water and minerals. Secondary functions include storage, reproduction, and protection. The internal structures of dicot and monocot leaves are compared. In summary, the document is an overview of leaf structure, function, adaptations and the differences between monocot and dicot leaves.
3. Characteristics of Leaf
•Leaf is an exogenous lateral
outgrowth
•It develops from the shoot meristems
of leaf primordia
•It has limited growth as the
intercalary meristem from which it
develops is consumed in growth
•Borne at the node of the stem
•Bears an axillary bud in its axil
•Green in colour due to photosynthesis
•Apical bud absent in the leaf
4. Functions of leaf
• Two types of leaf functions-Primary and Secondary
• Primary functions are Photosynthesis, gaseous
exchange
• Transpiration , conduction of water , protection of
buds
• Secondary Functions-Storage of water in succulents
, food in leaf base of Onion , air for buoyancy in
aquatic plants , reproduction in developing buds-
Bryophyllum
• Nitrogen fixation-by leaf nodules-Ardisia
• Modifications –for climbing-tendrils , spines, hooks,
plants, for support, catching insects in insectivorous
plants protection of buds , attracting insects for
pollination-Poinsettia
• Reducing transpiration-spines or phyllodes , form
pitchers to store water
5. Secondary functions of the Leaf
Mucilage storage-
succulents
Food storage-Onion Air storage-
Hydrophytes
Leaf buds-
Reproduction
Leaf nodules-
Ardisia
Pollination-
Poinsettia
6. PARTS OF A LEAF
• A typical foliage leaf consists of three parts: Leaf base ,
petiole and Lamina
• Lamina or leaf blade(Epipodium)-Thin ,expanded ,
green part of the leaf to perform photosynthesis
• Flattened lamina supported by veins and veinlets
• Contain vascular tissues for the conduction of water and
minerals and food
• Two faces of lamina-Adaxial-ventral or upper surface
• Abaxial-Dorsal or lower surface
• Leaves with two surfaces distinct-Dorsiventral leaves
• Leaves with similar surfaces-isobilateral(in monocots)
• Petiole(mesopodium)-Cylindrical or sub cylindrical stalk
of the leaf, lifts the lamina above the surface of the stem
to provide maximum exposure
• Leaf with a petiole-petiolate , without a petiole-sessile
• Peltate leaves-petiole attached to the centre of the
lower surface of the lamina , placed at right angles to
the petiole-Lotus
• Winged petiole-Lemon
8. PARTS OF A LEAF
Petiolate leaf Sessile leaf Peltate leaf Phyllode
9. PARTS OF A LEAF
• Leaf base(hypopodium or vagina)-Part of leaf joined to the node, indistinguishable from
the petiole
• Protects the young bud in the axil, in legumes swollen
• Responsible for sleep and shock movements in Mimosa pudica
• Pulvinus -Swollen leaf base
• Sheathing leaf base-Leaf base swollen broadened to enclose the stem
• Sheathing leaf base two types-Amplexicaul and Semi-amplexicaul
• Amplexicaul-Enclosing the stem completely-Grasses
• Semi-amplexicaul-Enclosing the stem partially-Buttercup
• Stipules-Leaf with lateral outgrowths-Stipules
• Stipulate-Leaf with stipules-Stipulate
• Exstipulate-Leaf without stipules-Exstipulate
• Ligule-Tongue shaped outgrowth present between leaf base and lamina
• Ligulate-Leaf with a ligule
10. PARTS OF A LEAF
Pulvinus Amplexicaul leaf base Semi-amplexicaul leaf base
11. PARTS OF A LEAF
• Stipules-Lateral outgrowths of the leaf base
• Types of Stipules
• Free Lateral-Small , free green outgrowths-Hibiscus
• Scaly-Small, membranous stipules-Cassia fistula
• Axillary-Fused to the innermost margins to become axillary-Gardenia
• Opposite-Fused from their outer margins to become opposite the leaf-Castor
• Interpetiolar-Adjacent stipules of the opposite leaves are fused to appear in petioles-Ixora
• Adnate-Stipules fused with the petioles to a distance so that the leaf base looks to be winged-Rose
• Ochreate-Stipules fused to form a sheath or ochrea around the stem-Rumex
• Convolute-Stipules of young leaves are connate and protect the bud ,fall as soon as the leaf unfolds-
Ficus
• Foliaceous-Large and green-Pisum
• Stipular spines-Stipules transformed into spines-Acacia
• Stipular Tendrils-Stipules are modified into chord like tendrils-Smilax
14. Types of leaves
• Foliage leaves-These are common green leaves for photosynthesis
• Scale leaves(Cataphylls)-Non green ,sessile, membranous structures
• Bracts(Hypsophylls)-Specialised leaves which bear flowers in their axil
• Bracteoles-Two small leaf like structures, found attached to the stalk of
the flower
• Prophylls-First one or two leaves of a branch which differ from the
other leaves
• Floral leaves-Special leaves which represent the vegetative parts of the
leaf
• Sporophylls-Modified spore bearing leaves of the flower
17. Reticulate Venation
• The veinlets form a network
• Found in dicots
• 2types-Pinnate or unicostate reticulate
venation,Palmate or multicostate reticulate
• Unicostate reticulate venation-Lamina has s
single principal midrib extending from base to
apex –Peepal
• Multicostate reticulate venation-Number of
prominent midrib which extend from base to
apex-2 types
• Convergent-Principal veins converde towards the
apex of the lamina-Zizyphus
• Divergent-Principal veins diverge towards the
margins-Castor
19. Parallel Venation
• Veins are inconspicuous ,veins run parallel to each other
• Characteristic of monocots exceptions-Smilax,Colocasia
• 2 types- Unicostate parallel venation, Multicostate parallel venation
• Unicostate parallel venation-Single principal midrib runs to of
lamina-Banana
• Palmate or Multicostate parallel-Several parallel arise from base of
the lamina
• 2 types-Convergent,Divergent
• Convergent-The principal veins converge towards the apex-Bamboo
• Divergent-The principal veins proceed toward the margins-Fan palm
24. Types Of Cyclic Phyllotaxy
Cyclic
Opposite
Opposite
decussate
Opposite
Superposed
Whorled
3 0r more
leaves
25.
26. Alternate or spiral Phyllotaxy
•A single leaf arises at each
node and the leaves of the
adjacent node lie the
opposite sides
•Spiral arrangement
•Appear to be arranged in
vertical rows
•Also called as Orthostichy
27. Schimper-Brown Series or Fibonacci
series
• A single leaf arises at each node and
the leaves of adjacent nodes lie on
opposite sides
• Arranged spirally on the stem and
appear to be in vertical rows
• Two vertical rows-1/2 distichous
• 3 rows-1/3 -tristichous
• 5 rows-1/2+1/3=2/5 pentastichous
• Number in numerator and
denominator of each fraction is the
sum of two preceding ones-Fibonacci
series or schimper brown series
30. Angle of Divergence
• The angle formed between two successive leaves and the centre of
the stem is called angular divergence
• Phyllotaxy ×360°=angle of divergence
• In distichichous=1/2 × 360°
• In tristichous=1/3 × 360°
33. Leaf Mosiac
•Present in sciophytes
•Leaves arranged in
close spiral
•Young leaves fit like
a mosaic in the
interspaces
34. Leaf Incision
•Incision is the cutting or notching of lamina
•The pattern depends on the type of venation
•Pinnate-In a reticulated venated, simple leaf
• Cutting from margins towards the mid-rib
•Palmate- Occurs in multicostate , reticulate venated , simple
leaf Cutting of lamina from the margins towards the base
•Types of incisions-Reaching up to half-fid, more than half-
partite , near the base of the midrib-sect
