Leaf structure, adaptations, development
- 1. Dr Jasmine Brar Email : drjasmine1807@gmail.com
- 2. Leaf: It is an exogenous, flattened lateral outgrowth developing at the node of the stem & bear bud in its axil. It is the major photosynthesizing & transpiring organ of the plant. Characters: Develop as an exogenous lateral outgrowth. Develops from shoot meristem as leaf primordia.
- 3. Its growth is limited (intercalary meristem). It is borne at node of stem. It bears an axillary bud in its axil. It is green due to chlorophyll. An apical bud is absent in leaf.
- 4. Accessory Function Storage of water, mucilage, salts in succulents Storage of food in leaf base of onion. Storage of air for buoyancy in aquatic plants. Reproduction in developing adventitious buds eg. Bryophyllum Reducing transpiration by phyllodes eg. Acacia Modified into pitchers to store rain water eg. Dischidia
- 5. Origin & Development of Leaf Develops from leaf primordium from promeristem of SAM i. Initiation: Periclinal divisions on flanks of promeristems below the apex. It produces a bulge called leaf buttress which grow laterally. Leaf primordium grows in length by activity of apical meristem present at tip. Further growth occurs by activity of apical, intercalary, adaxial & plate meristem.
- 6. ii. Development of leaf axis Apical meristem forms bladeless tapering cone shaped leaf-axis. Activity of apical meristem ceases & further development takes place by intercalary meristem. In monocots intercalary growth is more pronounced due to presence intercalary meristem.
- 7. iii. Growth of Lamina by Marginal Meristem 1. The cells of margins of leaf axis becomes more active & forms leaf blade with mid-rib (marginal meristem). 2. The marginal meristem of the leaf blade show little activity at base & form petiole. 3. Adaxial meristem divides periclinally & makes leaf thick. 4. Final shape & size of leaf takes place by activity of Plate meristem (meristem containing parallel layers of cells dividing anticlinally only)
- 8. Leaf primordia showing growing sites A. Apical growth B. Adaxial meristem, plate meristem & marginal meristem C. Intercalary growth D. Growth of blade derived from marginal meristem & vein differentiation
- 9. Vertical sections of leaf primordia showing Marginal & sub-marginal intials
- 10. Activities of marginal & sub-marginal initials (Dicot Leaf)
- 11. The activity of sub-marginal initials is not uniform in all leaves & follow two type of patterns
- 12. Type I: Alternation of anticlinal & periclinal divisions Anticlinal: Adaxial & Abaxial mesophyll layers Periclinal: Middle mesophyll layer
- 13. Type II: Anticlinal division: Submarginal initials & deeper inner layer are derived from abaxial/adaxial layers
- 14. The multiplication of mesophyll layer is variable in these two types of sequences. On completion of all layers, cells divide anticlinally only to increase the surface area but no change in thickness occurs.
- 15. Origin of leaf primordium /leaf blade in Flax (Linum) Leaf buttress Upward growth Primordium Before initiation of blade Growth of blade Plate meristem divides by anticlinal divisions
- 16. Still leaf compact Spongy parenchyma with intercellular spaces & pallisade tissue Mature Leaf Differentiation of mesophyll seen in Pyrus leaf
- 17. iv. Differentiation of Mesophyll 1. Palisade parenchyma is formed by anticlinal divisions 2. Spongy parenchyma is formed by anticlinal divisions but less frequent than palisade cells. 3. The adjacent epidermal cells stop dividing & enlarge in the plane parallel to the surface of the leaf.
- 18. v. Vascular Tissue Vascular tissue develop by activity of procambium that develops from plate meristem. Phloem develops earlier than xylem. The midrib & lateral veins are formed during intercalary growth.
- 19. Parts of leaf (Phyllopodium) a. Lamina b. Petiole c. Leaf Base Lamina: epipodium or leaf blade Expanded green part of leaf performing photosynthesis. It consists of veins which contains vascular tissue for conduction of water, mineral salts & food. Adaxial face: (Ventral/Upper) Abaxial face: (Dorsal/Lower) Dorsiventral leaves: In dicots 2 surfaces are distinct. Isobilateral Leaves: In monocots 2 surfaces are similar
- 20. Parts of typical leaf Peltate leaf of water lily
- 21. 2. Petiole (Mesopodium) Cylindrical stalk of leaf which lifts the lamina above the stem to provide exposure. Leaf having petiole is called petiolate & sessile if petiole is absent. Peltate: It is type of leaf insertion in which leaf lamina is at right angles to petiole. Eg. Lotus In lemon petiole is winged, partially winged & partially tendrillar petiole in Nepenthes, Clematis it is tendrillar & in Eichhornia it is swollen & spongy, Acacia petiole become leaf like called phyllode.
- 22. Lemon Water HyacinthStipels & pulvinus leaf base
- 23. Leaf Base/Hypopodium Part of leaf by which it is joined to the node of stem & it protects the young axillary bud. It is swollen in many legumes & is called pulvinus. It is responsible for sleep/shock movements of certain leaves. Eg. Mimosa pudica Sheathing leaf Base: Leaf base which is broadened to enclose the stem a. Amplexicaul: Enclosing stem completely eg.grasses, wheat. b. Semi-amplexicaul: Enclosing stem partially eg. Buttercup
- 24. Leaf base contain 2 lateral outgrowth called stipules & leaf containing them is called stipulate leaf. The one without stipules is called ex-stipulate. In Banana the apparent stem is only sheathing leaf bases one inside the other. Ligule: An outgrowth present b/w leaf base & lamina
- 25. Stipules Two small lateral outgrowth of leaf base which protect the young leaf & its axillary bud in young state. In compound leaves the leaflets bear basal lateral outgrowth: Stipels eg. Bean, Vicia Types of stipules 1. Free: Shoe flower 2. Scaly: Dry membranous in Cassia fistula 3. Axillary/intrapetiolar: Stipules fused from their inner margins to become axillary eg. Gardenia
- 26. 4. Opposite: Stipules are fused from their outer margins to become opposite the leaf eg. Castor 5. Interpetiolar: Adjacent stipules of opposite leaves are fused to appear in b/w the petioles. Eg. Anthocephalus (Kadam) 6. Adnate/Petiolar/Adherent: Stipules fused with petiole to a certain distance so that leaf base appears to be winged eg. Rose & groundnut. 7. Ochreate: Stipules fuse to form a sheath or ochrea around the stem eg. Rumex
- 27. 8. Convolute or protective scale or bud scales: Stipules of young leaves connate to protect bud & fall down as soon as leaf unfold. Eg: Ficus 9. Foliaceous: large & green eg. Pisum 10. Stipular spines: Stipules are transformed into spines. Eg. Zizipus. Two stipular spines of Zizipus are unequal with one straight & second hooked. 11. Stipular tendrils: Stipules are modified into cord like thick tendrils for climbing eg. Smilax
- 32. Types of leaves 1. Foliage Leaves: They are most common types of leaves for photosynthesis. 2. Cotyledons: They are seed leaves & they are 1 in monocots & 2 in dicots. Cotyledons nourish the embryo. After germination cotyledons manufacture food by becoming 1st foliage leaves. 3. Scale leaves/cataphylls: They are non-green, brown, Small, thin sessile & membranous structures. eg. Bud scales, scales on aerial stem like Ruscus.
- 33. 4. Bracts/Hypsophylls: They are specialized leaves which bears flowers in their axils. They protect the young floral Buds & when coloured they attract the insects. Eg. Bougainvillea 5. Bracteoles: They are two small leaf like structures which are found attached to the stalk of flower, aggregate to form whorls of epicalyx below the sepals. 6. Prophylls: They are the 1st one /two leaves of the branch which differ from other leaves. They form spines in Aegle (Bael) & Citrus.
- 34. 7. Floral Leaves: They are special leaves which represent Vegetative parts of flowers eg. Sepals, petals. 8. Sporophylls: They are modified spore bearing leaves of flowers eg. Stamens & carpels. 9. Stipules: They are two small leaf like lateral appendages Present at leaf base 10. Ligules: They are minute scale-like outgrowths present at the upper end of leaf sheath in grasses.
- 35. Size: Longest leaf of Raphia vinifera with size of 10-15 m Broadest leaf: Victoria amazonica (1.5-1.8 m diameter). It can hold upto 42 kg wt due to thick petiole & high buoyancy Smallest leaf: Wolffia Plants with single leaf: Monophylla Plants with only 2 leaves: Welwitschia
- 36. Venation Venation: The arrangement of veins & veinlets in the lamina of leaves Functions: 1. Conduction of water through xylem. 2. Providing channels for translocation of organic nutrients. 3. Conduction of minerals. 4. Provide skeletal support to lamina
- 38. I. ReticulateVenation The veinlets form a reticulum or network. It is found in dicots. Eg Calophyllum i. Pinnate or unicostate reticulate venation: Lamina has a single midrib which extends from base to apex. It gives rise to lateral veins along its entire length. Veins bear veinlets & veinlets form reticulations. Eg. Peepal, shoe flower. ii. Palmate or multicostate reticulate venation: A number of prominent veins arise from the tip of petiole & reach the apex. They give rise to lateral veins connected by reticulations of veinlets.
- 39. a. Unicostate of peepal B. Multicostate convergent of Ziziphus C. Multicostae divergent of Luffa
- 40. Multicostate reticulate venation (2 types) a. Convergent: The principal vein converge towards the apex of lamina eg. Zizipus b. Divergent: The principal vein diverge towards the margins eg Vitis, Cucurbits
- 41. II. Parallel Venation Veinlets are inconspicuous. Reticulations are absent. Veins run parallel to each other. It is present in monocots. Eg. Smilax, Colocasia It is of 2 types a. Pinnate/Unicostate Parallel venation b. Palmate/Multicostate Parallel venation i. Convergent ii. Divergent
- 42. a. Pinnate/Unicostate Parallel venation: There is a single principal vein/midrib that runs from base to apex of lamina. The lateral veins runs parallel to each other without anastomoses. eg. Banana, Canna b. Palmate/Multicostate Parallel venation: Several paralle veins arise from base of lamina. i. Convergent: The principal veins converge towards the apex. eg. Bamboo, grass ii. Divergent: The principal veins proceed towards the margins. eg. Fan palm (Livistonia)
- 43. A. Unicostate parallel of Banana B. Multicostate convergent of bamboo C. Multicostate divergent of fan palm Types of parallel venation
- 44. a. Furcate Venation: The veins branch dichotomously. The finer branches do not form a reticulum. It is common in ferns eg. Adiantum, Circeaster Furcate venation of Adiantum
- 45. Phyllotaxy The mode of arrangement of mature leaves on the stem & its branches. Reason: It is to avoid shading one another so that every leaf gets full light. It is of 3 types a. Alternate or spiral or Acyclic b. Cyclic Phyllotaxy i. Opposite ii. Whorled/Verticillate c. Leaf Mosaic
- 46. Alternate/acyclic Phyllotaxy ½ phyllotaxy, angular divergence = 180º
- 47. a. Alternate or spiral or Acyclic When single leaf arise at each node & leaf of adjacent nodes lie towards the opposite sides. They are arranged spirally around the nodes & appear to be arranged in vertical rows. This is called orthostichy. It may be in 2 vertical rows (1/2 of distichous phyllotaxy) 3 vertical rows (1/3 of tristichous phyllotaxy) 5 vertical rows (2/5 of pentastichous phyllotaxy)
- 48. 8 vertical rows (3/8 or octastichous phyllotaxy) 13 rows or (5/13 phyllotaxy) 21 rows or 8/21 phyllotaxy and so on…. Fibonacci Series or Schimper Brown Series of divergence ½, 1/3, 2/5, 3/8, 5/13, 8/21, 13/24, 21/55 i.e. here each number is the sum of the previous two. When this occurs, the angle between successive leaves or botanical element is close to the Golden Angle - about 137.5o
- 49. 1/3 phyllotaxy, angular divergence = 120º
- 50. 2/5 phyllotaxy, angular divergence = 144º
- 51. a. Parastichous arrangement of leaf bases on date palm trunk b. A pine cone showing Parastichous arrangement of sporophylls
- 52. b. Cyclic Phyllotaxy Definition: In the cyclic type of phyllotaxy the leaves at each node form a whorl with the leaves placed on a circle in which the angles between adjacent leaves are the same. i. Opposite: the two leaves at each node are always opposite one another. ii. Whorled/Verticillate: In this three leaves forming a whorl at each node. Eg. Nerium odorum. When it shows five or more leaves than it is called verticillate/whorled type. Eg. Alstonia scholaris.
- 53. c. Leaf Mosaic Definition: the arrangement of foliage in such a pattern as to expose the maximum number of leaves to the direct rays of the sun with little loss of intervening space. eg. common ivy, Acer pseudoplatanus, Oxalis, Garden Nasturtium. Incision Definition: A notch, as in the edge of a leaf.
- 54. Incision Pinnate leaf: is a compound leaf that is divided into smaller leaflets. It can either be even or odd, which is the amount of leaflets contained on the leaf.
- 55. Palmate leaf: is a compound leaf that has smaller leaflets attaching to a common point. The whole structure is "palm-like" and shaped like the palm of your hand. Pinnatifid: In this the clefts reach halfway or more to the midrib. Pinnatipartite: Here the leaves are pinnately divided into lobes reaching just over halfway to the midrib. Pinnatisect: Here the leaves are pinnately divided almost to the midrib but not into separate leaflets
- 56. Palmatifid: They are leaves having lobes with incisions that extend less than half-way toward the petiole. Palmatipartite: They are leaves having lobes with incisions that extend over half-way toward the petiole. Palmatisect: They are leaves having lobes with incisions that extend almost upto the petiole.