RBSE Solutions for Class 11 Biology Chapter 19 Leaf: External Morphology

RBSE Solutions for Class 11 Biology Chapter 19 Leaf: External Morphology

Rajasthan Board RBSE Class 11 Biology Chapter 19 Leaf: External Morphology

RBSE Class 11 Biology Chapter 19 Multiple Choice Objective Questions

Question 1.
Leaf Blade or lamina modified in peas
(a) Thoms
(b) scales
(c) Tendrils
(d) Stem

Question 2.
Swollen leaf base is called
(a) Pulvinus
(b) Sheathing
(c) Auriculate
(d) Pinnate

Question 3.
Parallel Venation is not found in-
(a) Maize
(b) Grass
(c) Wheat
(d) Banyan

Question 4.
In Pitcher plant, pitcher is modified of which part of leaf?
(a) Leaf apex
(b) Leaf Lamina
(c) petiole
(d) axis

Question 5.
Phyllode is modification of-
(a) Petiole
(b) Leaf Base
(c) leaf apex
(d) stem

Question 6.
Multipinnate compound or decompound leaf is an example of-
(a) Neem
(b)Babool
(c) Tamarind
(d) carrot

Question 7.
Leaflet tendril is an example of –
(a) Pea
(b) Cauliflower
(c) Carrot
(d) Potato

Question 8.
Absorbing leaves are found in
(a) In hydrophytes
(b) In Xerophvtes
(c) In Halophytes
(d) In Succulent

Answers:
1. c, 2. a, 3. c, 4. b, 5. a, 6. d, 7. a, 8. a

RBSE Class 11 Biology Chapter 19 Very Short Answer Type Questions

Question 1.
Reticulate venation is found in which plants?
Answer:
This type of venation is the characteristic feature of the dicotyledons such as Peepal and Hibiscus.

Question 2.
Swollen spongy petiole is found in?
Answer:
Nasturtium (Jal kumbhee).

Question 3.
Which part of the plant, food storage part of onion is ?
Answer:
A short stem that produces fleshy scale leaves or modified leaf bases).

Question 4.
Explain differnt parts of leaf with help of well labelled diagram?
Answer:
The leaf consists of three parts that are more or less well defined –

1. The leaf base (usually provided with a pair of stipules),
2. The petiole, and
   • The leaf blade or lamina.
     

Question 5.
Differentiate between Alternate and Opposite Phyllotaxy?
Answer:

1. Alternate or spiral: When single leaf is borne at each node and the leaves are arranged in such a way that a line drawn on the stem through the leaf bases takes a spiral course, the arrangement is called alternate or spiral or acyclic, e.g., Hibiscus, Mango, Ficus religiosa (Peepal), etc.
2. Opposite: The opposite phyllotaxy is the one in which a pair of leaves arise at each node on opposite sides. It is of two types.
   • Opposite superposed. All the pairs of leaves of a branch arise in the same plane so that only two vertical rows a leaves are formed, e.g., Jamun, Guava, etc.
   • Opposite decussate. A pair of leaves at one node stand: at right angle to the next upper or lower pair so that four vertical rows are formed on the stem, e.g. Calotropis, Zinnia, Tulsi, etc.

RBSE Class 11 Biology Chapter 19 Short Answer Type Questions

Question 1.
Differntiate between Stem branch and Compound leaf?
Answer:

Leaflets of a compound leaf	Simple leaf of a branch
The leaflets of a compound leaf are borne on a special axis called rachis. The rachis may represent the midrib or lateral vein of a simple leaf.	The simple leaves are directly borne on the stem. They are usually attached to the nodes of stem.
Leaflets of a compound leaf usually originate in the same plane.	Simple leaves are usually attached spirally on the stem. They may be alter­nate, opposite or whorled.
Leaflets do not bear stipules.	Leaflets do not bear stipules.
The leaflets do not bear buds in their axils.	The simple leaves bear axillary buds in their axils.
The leaflets of a compound leaf are generally fixed in number.	The number of simple leaves is not generally fixed.

Question 2.
Write about different types of leaf?
Answer:
The leaf consists of three parts that are more or less well defined –

1. The leaf base (usually provided with a pair of stipules),
2. The petiole, and
3. The leaf blade or lamina.

Question 3.
What is heterophylly ? Explain it with help of well labeled diagram?
Answer:
Occurrence of more than one shape of leaves in a plant is called heterophylly. It is common in some amphibious plants (e.g., Limnophila heterophylla). It is an adaptive significance of plant.

Question 4.
Differentiate between Opposite decussate and opposite superposed?
Answer:
Opposite: The opposite phyllotaxy is the one in which a pair of leaves arise at each node on opposite sides. It is of two types

1. Opposite superposed: All the pairs of leaves of a branch arise in the same plane so that only two vertical rows a leaves are formed, e.g., Jamun, Guava, etc.
2. Opposite decussate: A pair of leaves at one node stand: at right angle to the next upper or lower pair so that four vertical rows are formed on the stem, e.g. Calotropis, Zinnia, Tulsi, etc.

Question 5.
Differentiate between Free lateral stipules and Adnate Stipules.
Answer:

1. Free lateral stipules: These are two, small, green free stipules present on both lateral sides of the leaf base e.g.. Hibiscus rosa sinensis, Gossypium, etc.
2. Adnate stipules: These are two lateral stipules attached to/the petiole upto some distance but the anterior part remain free e.g., Rose, ground nut, Lupin etc.

RBSE Class 11 Biology Chapter 19 Long Answer Type Questions

Question 1.
Explain various modifications of Petiole with help of well labelled diagram?
Answer:
Petiole ( = Mesopodium):
A petiole or leaf stalk is a cylindrical or sub cylindrical structure of a leaf which joins the lamina to the base. A It raises the lamina above the level of stem so as to provide it with sufficient light exposure. A leaf with a petiole is called petiolate and the one without it is called sessile e.g., wheat, rice, Calotropis, Gloriosa, etc. Petiole bearing leaves are known as petiolate e.g., Peepal, mango, guava, Gossypium, Hibiscus rosa – sinensis etc.

Usually petiole is cylindrical with a long groove on upper surface. In some petioles groove is not present so it becomes cylindrical e.g., peepal. A Petiole raises the lamina high to provide more and more light and air. Mineral elements absorbed by root go into lamina through the petiole and food synthesized in the lamina go into stem through it. Petioles are of the following types-

1. Winged petiole: It is usually present in compound leaves. In this type petiole becomes flattened and leaf like and carry out photosynthesis like the leaf blade e.g., Citrus, orange, Feronia, sweet pea etc.
2. Phyllode: Lamina in some compound leaves falls off soon and petiole gets modified into leaf-like structure and synthesize food, e.g., Australian acacia and Parkinsonia. Phyllode develops usually in vertical direction to get least sunlight. This decreases transpiration.
3. Tendrillar petiole: Petioles in some weak stemmed plants is modified into tendril and help in climbing the plants e.g., Clematis, Nasturtium, Nepenthes etc.
4. Floating or bulbous petiole: In some plants viz. Eichhornia, Trcipa etc. petiole becomes spongy. This petiole is full of air and helps in floating.

3. Lamina ( = Epipodium) or Leaf blade:
The leaf lamina is normally a flat, thin, expanded, green and conspicuous structure where all the functions of leaf are carried on. It is the site of photosynthesis, gaseous exchange, transpiration and most of the metabolic reactions of the plant. The form, proportion and structure of lamina vary widely, not only between the leaves of different species but even among the leaves produced during the seedling and post seedling phases of a single species.

The leaf lamina are provided and supported by veins and veinlets which contain vascular tissues. It is made up of a thick middle line from petiole to the apex known as mid vein. Lateral veins arise from the mid vein, which later divide into small veinlets. These make a net like structure in the lamina. Each leaf has its own shape, two margins, one apex and two surfaces. According to shape, apex, margins and venation lamina has many variations.

There may be following shapes of lamina of leaf-

1. Acicular: In this type the lamina is like a needle, long thin and pointed e.g., Pinus.
2. Linear: In this type, lamina is long and narrow having parallel margins e.g., wheat, rice and grass.
3. Lanceolate: In this type, lamina is pear shaped i.e., thick at the lower side of mid-point and pointed at the ends e.g., Nerium, Bamboo and Polyalthea.
4. Oblong: This type of lamina is rectangular i.e., long, broad and with a round apex e.g., Banana.
5. Ovate: This type of lamina is egg or top shaped i.e., its base is wider than the apex, e.g., Banyan.
6. Cordate: In this type lamina is heart shaped i.e., its base is broad and lobed e.g.. Betel and Tinosporci .
7. Sagittate : This has arrow-shaped lamina i.e., lower side of lamina has pointed lobes on both sides having its direction on lower side e.g., Sagittaria and Arum.
8.  Hastate: In this type also the lamina is arrow shaped but both of the lower lobes of lamina are outwardly directed e.g., Ipomoea and Typhonium.
9. Reniform: In this type, lamina is kidney shaped i.e., lamina has a deep notch at the base e.g., Hydrocotyle and Malva.
10. Lunate: In this type lamina is semicircular e.g., Passiflora and in a fern (Adiantum),
11. Obovate: In this type lamina is like an inverted egg or top i.e., its apex is broader than base e.g.. Walnut, Primus amygdalus (Badam).
12. Obcordate: In this type lamina is like inverted heart i.e., its apex is broad and bilobed e.g., Bauhinia and Oxalis.
13. Spathulate: In this type lamina is like a spatula i.e., it is round and broader at the end and tapering at the base e.g., Dasy, Calandula, Lipia and Drosera.
14.  Cuneate or tunicate: In this type lamina is like the
    hood of snake i.e., its breadth increases towards its apex e.g ,,Pistia. .
15. Oval or elliptical: In this type also lamina is oval and its breadth is slightly less than its length e.g., Guava.
16. Orbicular or round: In this type lamina is circular and petiole attached below the lamina near its centre due to which lamina looks like an umbrella e.g., Lily, Nasturtium A leaf is called dorsiventral if its upper surface (the surface facing the stem or adaxial surface or ventral surface) differs in structure from its lower surface {i.e., abaxial or dorsal surface). On the other hand, the leaf is called isobilateral when the two surfaces are similar. However, some cylindrical leaves have no distinction of two surface.
    
    

Apex of Lamina: The apex of lamina is of the following types.

1. Acute: When the apex is pointed and soft and both of the margins of lamina meet to make an angle less than 90° (acute angle), it is known as acute apex, e.g., mango and Hibiscus rosasinensis.
2.  Acuminate or caudate: When the apex suddenly tapers and becomes very narrow to make a tail like structure it is known as caudate, e.g., Ficus religiosa, i.e., peepal.
3. Obtuse: When the apex is broad, round and blunt and both margins of lamina make an angle of more than 90° (obtuse angle) it is obtuse apex, e.g., Banyan.
4. Mucronate: When the apex is broad and round but has a small (projection) type e.g., Vinca rosea and Ixora.
5. Spiny or cuspidate: When the apex is pointed, hard and sharp like a spine it is known as spiny or cuspidate, e.g., Ananas, Datepalm, Kewra.
6. Tendrillar: When the apex is modified into tendril, which help in climbing of the plant, it is known as tendrillar, e.g., Gloriosa.
7. Cirrhose: When the vertical apex ends in a small, thin fibre like structure, it is known as cirrhose e.g., Banana.
8. Truncate: When the apex seem sharply cut it is truncate type, e.g., Parispolyphylla.
9. Retuse: When there is a notch at the apex it is known as retuse, e.g., Pistia and Clitoria.
10. Emarginate : When the notch, present at the apex becomes deep and divide it into two lobes, it is known as emarginate, e.g., Kachnar and Oxalis.
    

Margin of  Lamina:
Margin of lamina on the basis of incision is of following types-

1. Entire: In this type, margin of the leaf is smooth, and straight (i.e., nonincised) e.g., Banyan, mango, Smilax.
   Wavy or repand : In this type of lamina margin is wavy as in Saraca, Polyalthia.
2. Serrate: In this type of lamina margin is incised like a saw i. e.all teeth are directed upward e.g., rose and Hibiscus rosasinensis.
3. Biserrate: In this type of lamina margin have teeth which are incised like the teeth of saw e.g., Elm.
4. Retroserrate: In this type of lamina margins are incised like a saw but all the teeth are directed downwards.
5. Dentate: Margin of lamina in this type is like that of serrate, but teeth make right angle with the margin and these are directed outwards e.g., Water lily.
6. Bidentate: In this type of leaf lamina margins have teeth which themselves are directed outwards i.e., again dentate.
7. Crenate: In this type, lamina margin is toothed, but teeth are rounded e.g., Bryophyllum, Hydrocotyle.
8. Bicrenate: In this type, margins are cut into round teeth which themselves are cut into small round teeth.
9. Spiny: In this type, margin of lamina is spiny e.g., Argemone, Anannas etc.
10. Lobed: (Incised) In this type, margins are incised up to various depth and divided into small lobes e.g., Mustard and Raphanus sativs.
    

Basically there are three types of leaf:

1. Caducous: Such Leaves fall down within few days after it arises on plant. Example Cactus
2. Deciduous: Such leaves remains on plant up to a particular season. Example – Neem
3. Persistent: Leaves persist for many years on plants.

Kinds Of Leaves: On the basis of origin and function leaves are of the following types.
1. Cotyledonary Leaves: These are the embryonic leaves of seed. Usually these contain reserve foods, due to which these become fleshy e.g., beans and gram. In other plants as Ricinus these are thin and flat. In Geranium mole these are lobed. In monocot plants there is one cotyledon, called scutellum and in dicot plants are press two cotyledons.

2. Bract leaves or hypsophylls: Bracts are the leaves which contain flower or inflorescence in their axil. These are usually small and green but in some plants as Bougainvillea and Euphorbia; these are large and bright coloured. Usually their function is the protection of flower buds from sun and rain. Coloured bracts also attract insects for pollination.

3. Scale leaves or cataphylls : These are usually present on underground stems (e.g., rhizome) and are usually brown or grey coloured membranous structures. Actually, scales are small, sessile, chlorophylless leaves, Buds are present in their axil. Scale leaves are usually dry and act as a protective covering for buds e.g., ginger but in onion and garlic (underground bulb), scale leaves store food and become fleshy.

4. Floral leaves or sporophylis : Sepals, petals, androecium and gynoecium are modified leaves. These are known as floral leaves or sporophylis. Sepals are green and flat like a leaf. Petals are also leaf like, but the colour of petals is not green Both of these protect the reproductive organs (androecium and gynoecium) Corolla, being coloured, attract insects for pollination. Androecium an gynoecium take part in reproduction.

5. Foliage leaves : Normal leaves attached on aerial stem and branches at called foliage leaves. These are usually green coloured. These are flat. Main function of these leaves is to take part in photosynthesis, respiration and transpiration. The word ‘leaf’ is normally used for the foliage leaves.

Question 2.
What is venation? Explain different types of venation?
Answer:
Distribution pattern of the vein and veinlets in the lamina of a leaf is called venation. Internally, the veins contain vascular tissues (i.e., xylem and phloem) which provide the following functions to the leaves –

Xylem capillaries of the veins conduct water and minerals, Phloem components of the veins help in translocation of organic food, veins are strong enough to support delicate cells of lamina so that the later remains in stretched condition for optimum function, and veins and veinlets sustain the damaging effects of wilting. Venation is of two types –
(a) Reticulate
(b) parallel.
1. Reticulate venation:  The veinlet are irregularly distributed to form a network. This type of venation is the characteristic feature of the dicotyledons such as Peepal and Hibiscus. It is of two types –
(a) Unicostate:  It has only one principalvein or main vein which extends from its base to apex.
The main vein gives lateral branches to make a network, e.g., Peepal (Ficus religiosa), Mango (Mangifera indica), etc.

(b) Multicostate: It has several main veins of almost, equal thickness that arise from the base of lamina and transverse upto margins or apex.
The lateral veinlets, arising from main veins.form network. Multicostate venation is of two types –

1. Convergent: The. main veins converge towards the apex of the lamina, e.g; Smilax, Zizyphus, Nux vomica, etc.
2. Divergent: The main veins diverge towards the margins, e.g; Papaya, Cucurbita; Grape vine, etc.

2. Parallel venation: In case of parallel venation, the veins run parallel to each other and network is not formed. This type of venation is the characteristic feature of monocotyledons. It is of two types –
(a) Unicostate: The leaf lamina possesses single main vein which gives rise to a large number of lateral veins. All the lateral veins run parallel towards margin, e.g., Banana, Canna, etc.

(b) Multicostate: The leaf lamina possesses several main veins which run parallel to each other. Multicostate parallel venation is of two types

1.  Convergent: The main veins run parallel to each other and converge at the apex, e.g., Maize, Sugarcane, Wheat, Bamboos and Grasses.
2. Divergent: All the main veins of the leaf lamina spread out towards the margin, e.g., Fan palm (Borassus flabel lifer).
   

Question 3.
Difference between simple leaf and compound leaf? Explain different types of compound leaf with help of well labelled diagram?
Answer:
Compound leaves: In compound leaves, the lamina organization is most complex and characterized by the formation of separate leaf – like lobes called pinnae or leaflets attached in various ways to the portion of the leaf axis known as the rachis. There is one axillary bud in the axil of the whole compound leaf. The leaflets (pinnae or pinnules), however do not possess axillary buds. The compound leaves are of two typs.
(i) pinnate
(ii) palmate.
1. Pinnate Compound Leaves: It is the most familiar and widespread type of compound leaf in which the rachis is elongated and bears two rows of simple or divided leaflets. The leaflets may be arranged alternately or in pairs along the rachis. The pinnate compound leaves are of the following types-

1. Unipinnate. The leaflets are directly borne on the rachis (mid – rib). They are usually borne in opposite or sub opposite pairs. Unipinnate leaves are of two types –
   • Paripinnate. The unipinnate leaf with even number of leaflets, i.e. they are borne in pairs. Examples – Tamarindus indica, Cassia, etc.
   • Imparipinnate. The unipinnate leaf with odd number of leaflets. The rachis is terminated by single unpaired leaflet. Examples, Neem (Melia azadirachta), Rose, Murraya, etc.
2. Bipinnate: The pinnae are dissected again into pinnules. Thus, the main rachis produces secondary lateral branchescalled rachillae which bear the pinnules, e.g. , Acacia nilotica (vem. Kikar), Mimosa piidica (Sensitive plant);Caesalpinia, etc.
3. Tripinnate: The main rachis produces secondary’ rachis (rachillae) and it produces tertiary’ rachis which bear the pinnules. Thus, the leaf is thrice pinnate. Example: Moringa (vern. Sahijan).
4. Decomp ound: When the leaf is more than thrice pinnate (i.e., the incision is of a higher order than in tripimiate), it is called decompound. Examples – Carrot, Fennel, Coriander, etc.
   

2. Palmate Compound Leaves: In palmately compound leaves, the individual leaflets radiate in a digitate pattern from a very short rachis The leaflets may be petiolate or Sessile. These leaves are of the following types –

1.  Unifoliate: In this case, a palmately compound leaf is reduced to a single terminal leaflet. The single leaflet is articulated to the top of petiole, e.g.. Citrus (Khatta), Lemon, etc.
2. Bifoliate: This type of leaf has only two leaflets attached side by side at the terminal end of petiole, e.g,, Balanites roxburghii, Hardwickia binnata, etc.
3. Trifoliate: This type of leaf has three terminal leaflets, Aegle marmelos (Wood apple, ver. Bael), Oxalis comiculata, Trifolium (Clover), etc. These leaves differ from trifoliate imparipinnate (e.g., Lablab) in having all the three leaflets attached at the tip of petiole.
4. Quadrifoliate: The leaf has four leaflets attached to the tip of petiole, e.g., Paris quadrifolia.
5. Multifoliate: A palmately compound leaf having five or more terminal leaflets, arranged as fingers of the palm, e.g., Bombax malabarica; Cleome viscosa, Gynandropsis pentaphylla, etc.
    

   Leaflets of a compound leaf	Simple leaf of a branch
   The leaflets of a compound leaf are borne on a special axis called rachis. The rachis may represent the midrib or lateral vein of a simple leaf.	The simple leaves are directly borne on the stem. They are usually attached to the nodes of stem.
   eaflets of a compound leaf usually originate in the same plane.	Simple leaves are usually attached spirally on the stem. They may be alter­nate, opposite or whorled
   Leaflets do not bear stipules.	he simple leaves bear axillary buds in their axils.
   The leaflets of a compound leaf are generally fixed in number.	The number of simple leaves is not generally fixed.

Question 4.
Explain in detail various functions of leaf?
Answer:
(A) Primary functions:
1. Photosynthesis:  One of the most important functions of the green leaves is the synthesis of carbohydrates in presenceof sunlight. The leaves possess chloroplasts in their mesophylls which are primarily chlorenchymatous tissues. The chloroplasts possess chlorophylls and other accessory pigments of photosynthesis which trap solar energy and transform it into chemical energy in the form of carbohydrates.

2. Gaseous exchange: Leaves possess stomata in their epidermis which are the minute pores guarded by two kidney-shaped guard cells. The stomata are primarily meant for gaseous exchange required for photosynthesis and respiration.

3. Transpiration: Water, in the form of vapours, is mainly lost through the stomatal pores and expanded leaf surfaces. Loss of water in the form of vapours from living tissues is called transpiration. The process of transpiration helps tomaintain temperature of plant and assists ascent of sap.

4. Protection of bud: The terminal and axillary buds are protected by leaves from desiccation and mechanical injury.

5. Conduction: Vascular bundles present in the veins and petioles of the leaves serve the function of translocation of organic food through phloem and water and minerals through xylem.

(B) Secondary functions:
1. Storage: Succulent leaves of some xerophytic plants (e.g., Aloe, Agave, Kalanchoe, Sedum, etc.) store water, mucilage and food materials to resist drought. Fleshy leaf bases of Onion store food materials. The leaves of some aquatic plantsfc.g., Eichhomia, Nelumbo, Trapa, etc.) store air either in lamina or petiole for gaseous exchange and floating. Leaf lamina of some epiphytic plants (e.g., Dischidia) are modified into pitchers to collect rain water.

2. Protection: In some plants (e.g., Barberry, Opuntia, Argemone mexicana, etc.), the leaves or their parts are modifiedinto spines to protect the plants from browsing animals. In some xerophytic plants, the leaves are highly reduced or modified into phyllodes to reduce transpiration and protect the plant from desiccation.

3. Support: In some climbing plants, various parts of leaf get modified into tendrils which help the plants to climb the support.

4. Nitrogen nutrition:  Leaves of some insec-tivorous plants get modified into various forms of insect-traps. The leaves of Nepenthes and Sarracenia are modified into insect catching pitchers. The leaf segments of Utriculari a are modified to sac- like traps called bladders. These plants digest the insects and absorb nitrogenous substance to fulfil their nitrogen requirements.

5. Reproduction: Fleshy leaves of Bryophyllum develop adventitious buds in marginal notches which serve as means of vegetative propagation. Young leaves of Poinsettia pulchenima are brightly coloured which attract insects for pollination. The sepals, petals, stamens and carpels are modified leaves. They help in sexual reproduction of plants.

Question 5.
Explain the modifications of leaf in insectivorous plants?
Answer:
1. Storage Leaves: Some plants of saline and xerophvtic habitats and members of the family Crassulaceae commonly have fleshy or swollen leaves. These succulent leaves store water, mucilage or food materials. Such storage leaves resist desiccation, e.g., Aloe, Agave, Bryophyllum, Kalanchoe, Sedum, etc.

2. Leaf tendrils In some plants: the whole leaf or some of its part get modified into tendril. Tendrils are long, slender, wiry and coiled climbing organs which are very sensitive to touch and coil around a support with which they come in contact. Leaf tendrils are of the following types –

• Whole leaf tendrils. In this case the entire leaf is modified into tendril, e.g., Lathyrus aphaca (wild pea). In this plant, the stipules become foliaceous to perform the function of leaves. A small bud is present in the axil of tendril.
• Leaf tip tendril. In Gloriosa superba (Glory Lily, vem. Kulhari), the leaf apices are elongated and modified into tendrils.
• Leaflet tendrils – In Pisum sativum (vern. Pea) and Lathyrus odoratus (Sweet pea), the upper few  leaflets of pinnately compound leaves get modified into tendrils.
• Petiole tendrils – In some plants, the petioles become long and get modified into tendrils, e.g., Clematis (Virgin’s bower), Garden Nasturtium (Tropaeolum majus), Nepenthes, etc.
• Rachis tendril – In some plants, the tips of rachis (e.g., Lens culinaris, ver. Masur) or the entire rachis including the stalks of leaflets (e.g., Clematis) get modified into tendrils.
• Stipular tendrils – In Smilax, the free ends of adnate stipules are modified into tendrils.
  

3. Leaf spines: In some plants, the leaves or their parts are modified into spines.Plants develop spines in order to protect themselves from grazing animals. They are also formed as means of xerophytic adaptations to reduce loss of water by transpiration.

Leaf spines are of the following types:

• In Barberry, the leaves of main stem are modified into spines.
•  In Opuntia, the leaves of axillary buds are modified into spines.
•  In Phoenix and Yucca, the leaf apices are modified into spines.
• In Argemone, the margin of lamina is modified into spines.
• In Ulex, the leaves are modified into spines and the branches present in the axil of them are modified into thorns.
• In Zizyphus and Acacia, stipules are modified into spines.
  
  

4. Leaf hooks: In some plants, the leaves are modified into hook-like structures and help the plant to climb. In Bignonia unguiscati, the three terminal leaflets of the compound leaf get modified into stiff claw – like hooks (these hooks resemble the nails of cat). These hooks cling to the support firmly and help the plant to climb. The leaf spines of Asparagus also act as hooks.

5. Phyllodes: Phyllodes are flat, green coloured leaf-like modifications of petioles or rachis. The leaflets or lamina of the leaf are highly reduced or caducous. The phyllodes perform photosynthesis and other functions of leaf. They are xerophvtic modifications to reduce transpiration. Examples- Australian Acacia (Acacia -auriculiformis), Parkinsonia, etc. In Parkinsonia, the leaves are bipinnatelv compound. The primary’ rachis of each leaf is short and modified into spine. The secondary rachis are modified into phyllodes. The phyllodes of Australian Acacia are pendent, vertically placed and have few stomata to reduce transpiration.

6. Insect catching leaves In some insectivorous plants:
the leaves or their parts are modified into special insect catching organs. They catch insects, digest them and absorb its nitrogen to fulfill their nitrogen requirements. Some of the leaf modifications of insectivorous plants are –

1. Pitchers: In Nepenthes and Sarracenia, the leaves are modified into pitchers to catch and digest the insects. The pitcher of Nepenthes is modified lamina. The apex of leaf is modified into lid which covers the opening of pitcher.
2. Bladder: In Utricularia, the leaves are segmented. Some of the leaf lobes are modified into sensitive little sac- like traps called bladders. These bladders serve as floats for the water plant and act as traps for the insects.
3. Tentacles: In Drosera, the mature leaves , are spoon shaped and possess a large number of glandular hair, called tentacles. Each tentacle is stalked, mucilage- secreting gland which is very sensitive to touch. As soon as an insect comes in contact with lamina, the tentacles
   

7. Pitcher of epiphytic plant :
In epiphytic climber Dischidia rafflesiana, the whole leaf is modified into a pitcher provided with opening at the base.
These pitchers store rain water and debris. The same is absorbed by adventitious roots ( = nest roots) which grow out from the stem and ramify within the cavity.

8. Cataphylls (or scale leaves) : These are either dry and papery or fleshy leaves which do not take part in photosynthesis. They are mainly protective in function.

9. Floral leaves: Floral parts such as sepals, petals, stamens and carpels are modified leaves. Sepals and petals are leafy. They are protective in function and considered nonessential reproductive parts. Petals are usually coloured which attract the insects for pollination. Stamens are considered pollen bearing microsporophylls and carpels are ovule – bearing megasporophylls. Both stamens and carpels are essential reproductive parts.

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