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Transcript
Modified Structures - 1 We observed earlier several types of specialized roots. There are also a number of stem, leaf and shoot specializations beyond the leaf modifications discussed previously for different habitats. Some of these are discussed below. Modifications for Climbing or Clinging Vines Vines are stems that lack significant support tissue, and rely on other structures for their vertical support. Vines often have aerial roots to cling to their "host" structure, or, alternatively, have twining stems to wrap around the host structure, or tendrils to wrap around the host structure. Lianas are woody vines. Some examples of vines are: • English Ivy • Boston Ivy • Virginia Creeper • Tropical lianas • Common bindweed Clinging roots Tendrils Tendrils can be modified stems or leaves that are used to cling by coiling around the support structure. Most tendrils are pressure sensitive and show differential growth of the cells of the tendril to achieve the coiling. The direction of the coiling is also regulated. Some examples of plants that have tendrils are: • Peas (modified leaves) • Grapes (modified stems) Pea tendrils Grape tendrils Modified Structures - 2 Modifications for Propagation Rhizomes A rhizome is a non-fleshy underground horizontal stem. Rhizomes produce vertical shoots and adventitious roots at their nodes. Rhizomes are an ecologically successful adaptation for areas that have temperature or moisture extremes, since the underground stem is protected from these extremes, and can branch from nodes during better environmental conditions. Many prairie grasses are rhizomatous. Some examples of plants that produce rhizomes are: • Many grasses • Equisetum • Some Ferns Stolons or Runners A stolon is a non-fleshy horizontal stem that is above ground. Stolons branch from main portions of the plant, have elongated internodes, and produce "sprouts" at their tips. Most plants that produce stolons have basal stems with whorls of leaves. Some examples of plants that produce stolons are: • Strawberry • Spider plant Modified Structures - 3 Stem Modifications for Nutrient Storage and Propagation Tubers Tubers are fleshy (nutrient-storing) rhizomes that provide for survival during dormant periods. They are generally below ground, and are also capable of propagation in most cases. Some examples of plants that produce tubers are: • Potato • Ginger • Some Begonias Some Shoot Modifications for Nutrient Storage and Propagation Corms A corm is a dormant shoot system, with a compact, below ground, fleshy stem, surrounded by papery leaves. Corms are typically herbaceous perennials that die back to the underground corm to survive the unfavorable environmental season (i.e., winter). Corms are frequently (and mistakenly) called bulbs. Corms propagate by forming cormlets, which are buds that originate in the axils of the corm’s leaves. Some examples of plants that produce corms are: • Water Chestnut • Gladiolus • Crocus Modified Structures - 4 Bulbs A bulb is a dormant shoot system, with a compact, below ground, fleshy set of leaves (Technically bud scales), surrounding the shoot meristem. There is little nutrient stem storage in a bulb; nutrients are found in the fleshy leaves. Bulbs propagate by forming bulblets, which are buds that originate in the axils of the bulb’s leaves. Bulbs are also typically herbaceous perennials. Some examples of plants that produce bulbs are: • Onion • Daffodil • Tulip • Lilies Propagation Plantlets The formation of plantlets is a unique type of propagation. Some plants have the ability to form small new plantlets from leaf margins or the bases of the plant. If a stolon was not an elongated stem, the new shoots it produces at its tip could be considered plantlets. Some examples of plants that produce plantlets are: • Kalanchoe, • A number of “Maternity” plants Piggyback Plant Kalenchoe with plantlets Modified Structures - 5 Modifications for Defense: Thorns, Spines and Prickles Thorns, Spines and Prickles are designed for defense and protection. They are modifications of different plant parts. Thorns are branch systems typically found in leaf axils. An example of a plant that produces thorns is: • Hawthorn Spines are modified leaves or in some cases, the stipules of leaves. Some examples of plants that produce spines are: • Barberry • Cactus Prickles are extensions of epidermis and cortex tissue Some examples of plants that produce prickles are: • Roses • Blackberry Thorns Spines Prickles Modifications for water storage Succulents Succulents store water in special water storage parenchyma in leaves or in stems Some examples of succulent plants are: • Most things in the Crassulaceae have succulent leaves • A number of plants in the Cactaceae, Euphorbiaceae, Compositae and Asclepiadaceae families have succulent stems Frithia Buried leaf with "window" Jade Tree Modified Structures - 6 Special Stems Cladophylls Cladophylls are stems that resemble leaves Some examples of succulent plants that have cladophylls are: • Christmas cactus • Ornamental Asparagus (called erroneously the asparagus fern) Asparagus "Fern" Special Leaves Showy bracts Bracts are leaves that subtend (or are below) the inflorescence (the flowering shoot). In some plants these are showy, and take on the function of attracting pollinators, a function that is usually performed by the petals of flowers. Some examples of plants that have showy bracts are: • Poinsettia, • Bougainvillea • Dogwood (Cornus) Dogwood bracts Bougainvillea bracts Poinsettia bracts Modified Structures - 7 Carnivorous plants Carnivorous or insectivorous plants have modified leaves which are specialized to trap insects or other small animals. There are a variety of such plants, most of which are adapted to habitats where available nitrogen is scarce. They secrete enzymes that digest the protein of the captured animal to obtain sufficient nitrogen for growth. The method of trapping varies: • Some have trigger hairs that cause the leaves to fold over the insect • Some have sticky glandular hairs to which the insect sticks • Some have air bladders that aquatic animals swim into and cannot escape from • Some have cylindrical leaves with fluid in the bottom into which the insect falls, or slides, and then drowns, or gets trapped in. Some examples of insectivorous plants are: Sundew Cobra Lily Pinguicula (Butterwort) Pitcher Plant Modified Structures - 8 Utricularia (Bladderwort) Venus Fly-trap