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| Venation |
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| The arrangement of veins and veinlets in the leaf blade is known as venation. There are two types of venation. |
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| They are Reticulate venation and Parallel venation |
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| When the veins of a leaf show numerous irregular inter-connections giving the appearance of a network, it is called reticulate venation. This is characteristic of dicotyledons. |
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| It is of the following types: |
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| a. Pinnate or Unicostate Type |
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| If a leaf shows one vein more prominently than the others, it is described as unicostate condition. This prominent vein runs from the base of the leaf blade to its apex in a median longitudinal position. Hence it is the midrib of the leaf. The midrib produces veins which proceed towards the margin or apex of the leaf. These are then connected by veinlets forming a network. E.g., Mango, Peepul, Guava. |
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| Palmate or Multicostate Type |
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| If more than one prominent vein arises from the base of the leaf blade, it is described as multicostate condition. If the major veins converge towards the tip, then it is described as multicostate convergent (e.g. Zizyphus), or if they diverge, the venation is described as multicostate divergent (e.g. Cotton). |
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| fig. 27.34 Types of Venations in Leaf |
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| If the veins show a more or less parallel disposition, the condition is described as parallel venation. The parallely running veins are often connected at intervals by short links which are placed at right angles to the prominent parallel veins. Parallel venation is characteristic of leaves of monocotyledons. |
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| It is of the following types: |
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| a. Pinnate or Unicostate Type |
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| In this type, the leaf has a central prominent midrib. The midrib gives off lateral veins which proceed parallel to each other towards the margin or apex of the leaf, e.g. Banana. |
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| b. Palmate or Multicostate Type |
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| If more than one prominent vein arises from the base of the leaf blade, it is described as multicostate condition. A multicostate parallel convergent condition is seen in Bambusa arundinacea, whereas a multicostate parallel divergent condition is seen in Borassus. |
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