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A corm is a modified, upright, swollen, underground stem base of a herbaceous plant. Corms serve as a perennating organ, storing energy and producing new shoots and flowering stems from one or more buds located in the axils of the scale–like leaves of the previous year. Corms differ from superficially similar bulbs in that their leaves are thin rather than fleshy, and they are entirely composed of stem tissues.

Herbaceous plants are perennials, meaning that they have a lifespan of several to many years. However, after each growing season the above-ground parts of herbaceous plants die back to the ground, and new growth must issue from below ground to begin the following season. In the case of cultivated species such as gladiolus (Gladiolus communis), crocus (Crocus sativus), and water chestnut (Eleocharis tuberosa), the new herbaceous growth develops from underground corms. In fact, the corm of the water chestnut is eaten.

Horticulturalists usually propagate these species using corms, which develop small "cormels" from lateral buds on the sides of the parent corm. A relatively vigorous production of cormels can be stimulated by wounding the parent corm, for example, by making some sharp but shallow cuts on its base. To cultivate these plants, the cormels are split off and individually planted, right-side up, and a new plant will develop. The use of corms to propagate new plants in these ways does not involve any exchange of genetic information, and is referred to as vegetative propagation because the parent and progeny are genetically identical.

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Science EncyclopediaScience & Philosophy: Condensation to Cosh