Leaves are green flat structures borne on the stem or on the braches. Leases arise from the nodes. I hey have buds in their axils. Lein es increase the surlitee area kw absorption of sunlight. They prepare lbod by photosynthesis. They also carry on transpiration.
Parts of leaf
A typical foliage leave consists of three parts:
I. Leaf blade or lamina: The lamina is green expanded portion o leaf. It performs photosynthesis.
2.Petiole: The leaf stalk is called petiole. It raises the lamina trmards sunlight. It is absent in some leaves. Therefore. lamina is directly attached ‘t, ith the stem.
3.Leaf base: la:al base is the part of leaf which attaches to the stem. It forms sheathing in mans monocotyledons. 1 he leaf bases in many DicoR ledons bear t \ti out growths called stipules.
Chief types of Leaves
There are following chief types of leavess:
I. Foliage leaves: The ordinary. green leaves which carry on
photosynthesis are called foliage leaves
2.Cotyledonary leaves: the lea is thund in seeds vs hick store food are called cotyledonary leaves.
3.Scale leaves: The small. undo, eloped. ,sessile and colourless lea es are called scale letnes. They are protective leaves. ‘Hwy protect the young foliage lea N. es in bud. They are developed in many underground stems like stickers. bulbs. rhizomes corm etc.
4.Bracts and Bracteoles: The special leaf in the mil of which flower arises is called bract. These are usually small and scale like. They may be green or coloured. One or two leaves present on the stalk of Hosier are called bracteoles. The primary Iii nction or bracts and bracteoles are to protect the flower from sunlight and rain.
5.Floral leaves: The specialized leaves which form the part of flower are called floral leaves. ‘hese are sepal, petal. stamens and carpels.
Pair or ootarowths developed at the base of the petiole of a leaf are called stipules. Stipules are present in many angiosperm plants. If the stipules are present. the leaf is called stipulate. If the stipules are absent, the lea F is called ex-stipulate. Some stipules remians in place as long as the leaf persists. Such stipules arc called persistant stipules. Some stipules hill off as soon as the leaf unfolds. Such stipules are called deciduous stipules. The stipule like structures present at base of leaflets of a compund leaf are called stiples. There are following ty pes of stipules:
Fig: Different types of stipules
1.Scaly stipules: These are small. membranous and scaly stipules. They protect the bud. .lhey drop off as soon as the bud unfolds. They are found in peepal.
2.Leafy stipules: These are large greiii and leaf like stipules. they are edible in some plants likt sweet pea. In sonic plants like edible pea. these are modi lied into tendrils.
3.Free lateral stipules: –Nese are small and green stipules. present freely– at the base of petiole. lixample cotton
4.Adnate stipules: The w ings like stipules which are fused laterally w ith the petiole are called adnate stipules Example: rose
5.Interpetiolar stipules: ihese stipules are present laterally between the petioles of opposite lea x es. Example coffee plant
6.Asillary stipules: In this ease. the stipules of a leaf fuse to form a single stipule. It is prescnt between stein and petiole.
7.Oehreate Stipules: In this case, large stipules fuse along their margins to form a Maim tube called area. Ochrea surround the stem from the node to certain height of internodes. Example: Polygonum.
8.rendreliar Stipules: In sonic cases. the stipules are modified into tendrils. These arc called tendrillar stipules. Example: Smilax.
9.Spinous Stipules: In sonic cases. stipules are modified into spines. Such stipules are called vinous stipules. example:
Acacia , Zityphus jujha
The arrangement of the lea vs on the stem is called phyllotaxis.
Illy I lotaxis reduces overriding Therefore. the leaves get
‘maximum sunlight There are two main types of phyllotaxis:
I. Spiral: The phyllotaxis in which single leaf borne at each node is called spiral phyllotaxis. In this case, the leaves are
called alternate. Examples: Sunlltmer. mustard
2. Cyclic: The phyllotaxis in which two or more leaf borne at each node is called cyclic phyllotaxis. There are mu lorms of cyclic phy llotaxis:
(a) Opposite: In this case. only Rso leaves arise at each node. They are arranged opposite to each other..Fhis condition is called opposite. There are ty%0 forms of opposite cyclic phy llotaxis:
Opposite and superposed: In this case, the opposite leaves of different nodes are parallel to each other.
Opposite and decussate: In this case, the opposite lea es form Our runs On the stem. Example: mitit
(a) Whorled: In this case, more than mo leaves are present at each node. These leaves are arranged in a circle around the node.
The arrangement of veins and veinlets. in the lamina of a leaf is called venation. ‘Elie wins and einlets transport water and dissolved minerals into various parts of the leaf. I hex also car) the prepared material from leaf to stem. I he lamina ma) have one or more principle veins or midribs. [here are two types of venations:
I. Parallel venation: The venation in which many veins of equal size run parallel to each other from the base to ape). or from midrib to margin of leaf is called parallel venation. Parallel enat ion is characteristics of monocots plants like grasses. onion and banana.
a.Pinnate or unicostate: In this case. leaf has a single prominent vein. It gi) es off lateral branches. ‘I’hese branches run parallel to each other to the margin of leaf. Example: banana
b.Palmate or multicostate: In this case. the principle wins run parallel to each other. It ma) be convergent or div ergent. Example: grasses. rice.
2. Reticulate venation: The venation in which smaller veins arise from the midrib and form network is called reticulate venation. It is found in dicot plants like, gram etc. It has Rs° types:
(a) Pinnate or Unicostate: In this case. the leaf has single midrib. It gives off lateral branches Ii ic Ii run to ards the margin or the leaf The veins giv e MT smaller branches in all directions and form a netssork. I ample: mango. guava
(b) Palmate or Multicostaie: In this case. the leaf has mans, principle %chi% of equal si/e. ‘these seirts arise from the base of lamina and form netssork. Ihis enation may he convergent or divergent.
1.Caducous: If the leaf fall off set.) early. it is called caducous. Example: Opuntia
2.Deciduous: In this case. the leaf ills MT at the end cif each cross ing season.. Example: \ hither’)
3.Persistant: In this case. the leases remain functional on the plant lOr more than one season. The plants ss ith persistant leaves are called evergreen plants.
The attachment of leaves to the stein or branches is called insertion of leaf. irhese are:
I. Cauline: In this ease. the leases develop on the main stein. ksamples: sunllosser
Rental: In this case. the leases develop on the branches. Example: Mango
Radical: In this case. the leases appear to come out from roots. Example: radish, beet.
Presence or Absence of Petiole
I. Petiolate: In this ease. leaf stalk or petiole is present. Example: leaf of mango:
Sessile: In this case, petiole is absent. Example: Poppy
Sub-sessile: In this case. petiole is very small.
Peltate: In this ease. petiole is inserted near the centre of lamina.
Forms Of Leaf Bases
1. Amplexicual: In this ease. leaf base is flattened and clasps round the stem completely at the node. Example: Fennel
2.sheath completely surrounds the losser half of the internode. Example: leaf of many grasses like w, heat, maize etc.
3.Connate: In this case. bases of two opposite leave meet each other and fuse together across the stem. Example: Zinnia.
5.Ligulate: In this case, a hairy or membranous outgrowth is present at the junction of the lamina. Example: rice, wheat. sugarcane.
Surface of leaf
I. Flaky: In this case, leaf is co‘ ered ith hairs. I.xample: radish
2. Prickly: In this case, lea I has prickles: rose
A leaf in which lamina is divided into number of separate leaf like parts called leaflets is called compound leaf. Leaflets arise from one point or they borne on a common stalk or rachis. Thus there are two types of compound leaves:
Pinnate compouml leaf: The compound leaf in which leaflets arise from the sides of the rachis is called pinnate compound leaf. Example: leaf of rose
Palmate compound leaf: I he ek impound leaf in which leaflets arise from one point at the tip of the petiole is called palmate compound leaf.
I. Leaf tendrils: In sonic cases. lea es are modified into tendrils.
For example the whole leaf is modified into tendril in wild pea.
Leaf spines: In some plants, entire leaves or part of leaves are modified into spines. Example barberry.
Leaf pitcher: The leases are modified into leaf pitchers in insectivorous plants. It is found in pitcher plant (Nepenthes). A lid is present at the upper end of pitcher.
I.eaf bladder: Leaf bladders arc found in rootless. submerged insectivorous plants. In this case, the leaves are modified into segments. Some of the segments form bladders. Example: Illadderwort ( (Itricularia I.
PhyHodes: In sonic plants. the compound lamina of leaves becomes less developed. Ehe petiolebecomesflattened.Finally the lamina is degenerated and shoots bears
Fig.. Different type leaf inticlificalions