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Unformatted text preview: 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 and Lianas 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 of Vines and Lianas 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 (Asexual Reproduction) Rhizomes A rhizome is a "non-fleshy", but often sturdy, 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. Shoots can branch from nodes during better environmental conditions. Many prairie grasses are rhizomatous, as is Equisetum , a spore-dispersing vascular plant. Some examples of plants that produce rhizomes are: • Many grasses • Equisetum • Iris • Many 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"...
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This document was uploaded on 01/06/2012.
- Spring '09