Download Modified Structures - 1 We observed earlier several types of

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
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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
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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
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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
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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
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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
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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
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Utricularia (Bladderwort)
Venus Fly-trap