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| Virtually the entire root system is adventitious in many ]s, especially ]s, ] and most ]s, e.g. ]es. In most monocot species, the radicle never develops to any extent, and adventitious roots form at the base of the stem. Such adventitious root systems are also termed fibrous root systems. Root systems of specialized underground stems (]s, ]s, ]s, ]s) are all adventitious roots. The tap root systems of most ]s and ]s develop from the primary root but even they often develop some adventitious roots when the old roots or lower stem is wounded. Horizontal, aboveground stems, termed ]s or runners, usually develop adventitious roots at their nodes, e.g. ].blarg | Virtually the entire root system is adventitious in many ]s, especially ]s, ] and most ]s, e.g. ]es. In most monocot species, the radicle never develops to any extent, and adventitious roots form at the base of the stem. Such adventitious root systems are also termed fibrous root systems. Root systems of specialized underground stems (]s, ]s, ]s, ]s) are all adventitious roots. The tap root systems of most ]s and ]s develop from the primary root but even they often develop some adventitious roots when the old roots or lower stem is wounded. Horizontal, aboveground stems, termed ]s or runners, usually develop adventitious roots at their nodes, e.g. ].blarg | ||
| ==hello willow. | ==hello willow.dadhdhdhfhuifruigyr | ||
| ==Location of origin== | ==Location of origin== | ||
Revision as of 23:19, 30 October 2006
Adventitious, in botany, refers to structures that develop in an unusual place, and in medicine, it refers to conditions acquired after birth. This article discusses adventitious roots, buds and shoots, that are very common in vascular plants.
Adventitious roots
Adventitious roots develop on stems, leaves and even old roots. The radicle or primary root and its lateral roots are the only nonadventitious roots. Many aerial stems naturally form aerial roots. There are two types of adventitious roots. Aerial stems often have preformed root initials at nodes that will develop into roots given the proper conditions. Other adventitious roots are termed wound roots, because they do not form until the stem, root or leaf is wounded.
In some species, adventitious roots form on aerial stems, grow down into the soil and help keep the stems upright, e.g. prop roots of maize, screwpine and banyan. Some vine stems cling to their supports using adventitious roots, e.g. English ivy and philodendron. Adventitious roots may also form naturally when an aerial stem contacts the soil, e.g. arching branches of forsythia, blackberry and weeping willow. Some trees, such as willow, naturally shed pieces of twigs, a phenomenon known as cladoptosis. The shed twigs are often transported via rivers and streams and can form new plants if they develop adventitious roots.
Virtually the entire root system is adventitious in many vascular plants, especially ferns, fern allies and most monocots, e.g. grasses. In most monocot species, the radicle never develops to any extent, and adventitious roots form at the base of the stem. Such adventitious root systems are also termed fibrous root systems. Root systems of specialized underground stems (rhizomes, bulbs, tubers, corms) are all adventitious roots. The tap root systems of most dicots and gymnosperms develop from the primary root but even they often develop some adventitious roots when the old roots or lower stem is wounded. Horizontal, aboveground stems, termed stolons or runners, usually develop adventitious roots at their nodes, e.g. strawberry.blarg
==hello willow.dadhdhdhfhuifruigyr
Location of origin
Adventitious roots and buds usually develop near the existing vascular tissues so they can connect to the xylem and phloem. However, the exact location varies greatly. In young stems, adventitious roots often form from parenchyma between the vascular bundles. In stems with secondary growth, adventitious roots often originate in phloem parenchyma near the vascular cambium. In stem cuttings, adventitious roots sometimes also originate in the callus cells that form at the cut surface. Leaf cuttings of the Crassula form adventitious roots in the epidermis.
Vegetative propagation
Adventitious roots and buds are very important when people propagate plants via cuttings, layering, tissue culture. Plant hormones, termed auxins, are often applied to stem, shoot or leaf cuttings to promote adventitious root formation, e.g. African violet and sedum leaves and shoots of poinsettia and coleus. Propagation via root cuttings requires adventitious bud formation, e.g. in horseradish and apple. In layering, adventitious roots are formed on aerial stems before the stem section is removed to make a new plant. Large houseplants are often propagated by air layering. Adventitious roots and buds must develop in tissue culture propagation of plants.
References
- Esau, K. 1977. Anatomy of Seed Plants. New York: Wiley.
- Hartmann, H.T. and Kester, D.E. 1983. Plant Propagation: Principles and Practices. Englewood Cliffs, NJ: Prentice-Hall.