BSC 314 Lecture Notes - Lecture 9: Root Cap, Xylem, Meristem
26 Jun 2018
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Types of Root Systems
Plants have three types of root systems: 1.) taproot, with a main taproot that is larger and
grows faster than the branch roots; 2.) fibrous, with all roots about the same size;
3.) adventitious, roots that form on any plant part other than the roots. Fibrous systems are
characteristic of grasses and are shallower than the taproot systems found on most eudicots
and many gymnosperms.
Specialized and Modified Roots
Roots often perform functions other than support and absorption. Some store starch
(beets and turnips) or water (desert plants). Pneumatophoresare roots that grow into
the air and are filled with a specialized parenchyma called aerenchyma. The large,
intercellular spaces of aerenchyma are filled with oxygen and other gases. The
pneumatophores seem to assist in aerobic respiration and gas exchange and are
abundant on woody plants like cypress and mangrove, which grow in water logged ‐
soils.
Some roots produce suckers from adventitious bud-like growths. Suckers grow into aerial
shoots capable of independent existence, and serve to propagate the plant. Because they
have the same genetic make-up as the parent plant, they are clones of the parent. Aspen
groves in the western United States frequently are clones of only one or a few parent trees.
Many flowering plants develop as parasites on other plants. They produce adventitious roots
called haustoria that penetrate the tissues of the host and connect to the vascular system,
thus becoming part of the host pipelines. Parasitic roots lack most of the tissues of ordinary
roots. Dodder and mistletoe are two of the more than 3000 flowering plant parasites.
Mycorrhizal roots are known from 90 percent of plant species and are a mutualistic
association of a fungus with plant root tissue. Most plants require specific mycorrhizal fungi
without which they are unable to absorb sufficient quantities of P, Zn, and Mn. The fungus
takes the place of root hairs and may penetrate the cortex completely (endomycorrhizae) or
remain on the surface of the root ( ectomycorrhizae).
Root Zones
In most vascular plants, roots are underground structures that anchor the plant and
provide a means to absorb the nutrients and water needed for growth of the plant body.
New root tips grow continuously throughout the life of the plant and provide the surfaces
through which most of the nutrients and water move. Roots are used as storage organs
for the food materials produced by the shoots. The major functions of roots, thus, can
be summarized simply as absorption, conduction, storage, and anchorage.
As cells are added to the tip by repeated cell divisions, a young root elongates and
leaves behind cells that differentiate and become the primary roots of the plant. Four
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Document Summary
Plants have three types of root systems: 1. ) taproot, with a main taproot that is larger and grows faster than the branch roots; 2. ) fibrous, with all roots about the same size; 3. ) adventitious, roots that form on any plant part other than the roots. Fibrous systems are characteristic of grasses and are shallower than the taproot systems found on most eudicots and many gymnosperms. Roots often perform functions other than support and absorption. Some store starch (beets and turnips) or water (desert plants). Pneumatophoresare roots that grow into the air and are filled with a specialized parenchyma called aerenchyma. The large, intercellular spaces of aerenchyma are filled with oxygen and other gases. The pneumatophores seem to assist in aerobic respiration and gas exchange and are abundant on woody plants like cypress and mangrove, which grow in water logged soils. Some roots produce suckers from adventitious bud-like growths.
