A typical foliage leaf has three main parts. –
1. Leaf base
2. Petiole
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3. Lamina.
Leaf base
The part of leaf attached to the stem or branch is known as leaf base. Usually it is broader to get sufficient base for attachment. Different plants have different types of leaf bases which are as given below:
1. Pulvinus : Most of the leaves have a swollen leaf base known as pulvinus. Its attachment on the stem is not strong. So leaves with such leaf bases can be plucked easily e.g., mango, beans, banyan tree, gulmohar, gram, pea, Tamarindus and Mimosa pudica plant.
2. Sheathing : In monocot stem leaf base becomes broad and flat and covers a part of the node of stem. Zea mays, sugar-cane, banana etc. In banana, sheathings of many leaves jointly make a stem like structure known as false stem. True stem in banana is the underground stem.
3. Decurrent : In some plants petiole and leaf base, both become broad, flat and winged. These ensheath the upper part of node e.g., Symphytum Laggera, Crotolaria etc.
4. Amplexicaul : When sheathing leaf base clasps and surround the stem completely e.g., Polygonum
Petiole
Petiole is the part of leaf connecting the lamina with the branch or stem. Its upper part remains embedded in lamina in the form of mid rib, and lower part remains attached with the branch in the form of leaf base. Leaf is called sessile when there is no petiole 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. 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 (Fig. 7.5 D), Trapa etc. petiole becomes spongy. This petiole is full of air and helps in floating.
LAMINA
This is the most important green and flattened part of the leaf. 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. The main function of the lamina is to synthesize food, respiration and transpiration. Each leaf has its own shape, two margins, one apex and two surfaces. According to shape, apex, margins and venation-lamina has many variations.
Shape of Lamina :
There may be following shapes of lamina of leaf –
1. Acicular : In this type the lamina is like a needle, long thin & 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 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 Tinospora.
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, Prunus 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 rotund : 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 and Lotus.