MODIFIED / SPECIALIZED PLANTS
Some leaves have special functions along with or instead of food making. These are the examples:
* Protective leaves
* storage leaves
* Insect-capturing leaves.
* Shade Leaves
Protective leaves include bud scales, prickles, and spines. As described earlier, bud scales are specialized leaves that protect the young, undeveloped tissues of the bud. Bud scales are short and broad, and they overlap like roof shingles. In many plants, the bud scales have an outer layer of waterproof cells. Prickles and spines are sharp leaf structures that protect the plant from being eaten. For instance, prickles cover the leaves of the Canada thistle. The prickles protect the plant from grazing animals. Many cactuses have clusters of spines. In many species of cactuses, the pointed spines replace the leaves on the mature plants. In these plants, the green stem has the job of photosynthesis. * Storage Leaves-Succulent leaves are leaves modified to retain and store water. Water storage is permitted because of the thin-walled, non-chloroplast parenchyma cells just beneath the epidermis and to the interior of the chlorenchyma tissue. The vacuoles in the non-photosynthetic cells store the extra water resources. There are plants with succulent leaves that have a special photosynthetic process. We will look at these in a later tutorial. The fleshy leaves of onions and lily bulbs store large amounts of carbohydrates which are utilized by the plant in the next growing season. * Tendrils are slender, whip-like structures that help hold climbing plants in place. They wrap around twigs, wires, and other solid objects. Among many climbing plants, specialized leaves serve as tendrils. For example, climbing garden peas have compound leaves in which the upper leaflets are threadlike tendrils. In one kind of sweet pea, a garden flower, the entire leaf blade becomes a tendril. The plant's stipules enlarge and take over the food-making job. In the greenbrier vine, the stipules form long, curving tendrils. * Bracts grow just below the blossoms of certain plants. Most bracts are smaller and simpler in shape than a plant's regular leaves. Many members of the daisy family-including daisies, goldenrods, marigolds, and sunflowers-have bracts. These bracts form a cup beneath the plant's cluster of flowers. A few kinds of plants, such as the flowering dogwood and poinsettia, have large, showy bracts. These bracts look like part of the flower, but they are not. * Insect-capturing leaves. Carnivorous (meat-eating) plants, such as the butterwort, pitcher plant, sundew, and Venus's-flytrap, have leaves that capture insects. These leaves, like other leaves, can make food using sunlight. But they also have features that attract, trap, and then digest insects. Plants with insect-capturing leaves grow in wetlands, where the soil contains little nitrogen. They obtain this necessary nutrient from the captured insects. For a description of these plants and their leaves. * Shade Leaves-In some plants, leaves with barely noticeable or unnoticeable modifications will occur right alongside those that are unmodified. Leaves in the shade tens to be thinner and have fewer hairs than those on the same tree exposed to direct light. In addition, they are generally larger and have less defined mesophyll layers and reduced numbers of chloroplasts than their better lit counterparts. SPECIALIZED STEMS
Although typical shoots are erect with photosynthetic leaves, over evolutionary time a great assortment of modifications of the basic body plan have arisen. Some clearly benefit storage of materials, others assist in vegetative reproduction (reproduction without seeds), various alterations deter herbivores, and many are simply innovations in ways to hold the shoot upright. The most bizarre of all may be the leaves of the insectivorous...
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