Some leaves have special functions along with or instead of food making. Such specialized leaves include (1) protective leaves, (2) storage leaves, (3) tendrils, (4) bracts, and (5) insect-capturing 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. Most plants store food in their roots or stems. However, some plants have special leaves that hold extra food. Onion and tulip bulbs, for example, consist mainly of short, fat storage leaves called bulb scales. These leaves cannot make food. Their job is to store food underground during the winter months.
BULB. Many plants that grow in dry places have thick leaves that store water. The mosslike stonecrop plants that grow on rocky cliffs in the Southwestern United States have such leaves.
Tendrils are slender, whiplike 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. <<