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| Modifications of Leaves |
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| A normal leaf is thin, flat and green and performs the function of photosynthesis. In some plants certain special functions are performed by leaves, which become modified. |
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| Tendrils are slender, spirally coiled springlike structures. They are highly sensitive to contact and when they come in contact with any support, tendrils coil around the support like the stem twiners. |
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| In glory lily (Gloriosa superba) the leaf apex is modified into a tendril. In pea (Pisum sativum) the terminal leaflets of an unipinnately compound leaf are modified into tendrils. In Lathyrus or wild pea, the entire leaf is modified into a tendril. In Clematis and Smilax, the petiole and stipules respectively, are modified into tendrils. |
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| A phyllode is the petiole or rachis of a leaf which is modified into a green flat structure for the purpose of photosynthesis. In such a leaf the lamina is poorly developed. In Acacia melanoxylon, the petiole is flattened, green and becomes a phyllode. The leaflets and secondary rachii drop off. |
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| In Parkinsonia aculeata, the secondary rachii are modified into phylodes which are photosynthetic. The primary rachis is modified into a spine. |
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| In some plants, leaves or parts of leaves may be modified into spines. |
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| In Opuntia (prickly pear) leaves are poorly developed and fall of very early, but the minute leaves of the axillary bud are modified into spines. In Argemone (prickly poppy), the leaf margin is modified into small spines. In Zizyphus the stipules are modified into spines. The spines act as defensive structures. |
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| fig. 27.38 - Leaf Spines |
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| In many desert plants, the leaves are highly reduced and appear as scales. The scale leaves are thin, membranous, dry, stalkless and brownish or colourless. In plants where the leaves are reduced to scales in order to minimise transpiration, the function of photosynthesis is relegated to the stems (cladodes). |
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