corm

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Taro corms for sale in a Réunion market

A corm is a short, vertical, swollen underground plant stem that serves as a storage organ used by some plants to survive winter or other adverse conditions such as summer drought and heat (estivation). A corm consists of one or more internodes with at least one growing point, with protective leaves modified into skins or tunics. The thin tunic leaves are dry papery, dead petiole sheaths, formed from the leaves produced the year before, which act as a covering that protects the corm from insects and water loss. Internally a corm is mostly made of starch-containing parenchyma cells above a circular basal node that grows roots.

Comparison of the corm and the bulb

Corms are sometimes confused with true bulbs; they are often similar in appearance to bulbs externally, and thus erroneously called bulbs. Corms are stems that are internally structured with solid tissues, which distinguishes them from bulbs, which are mostly made up of layered fleshy scales that are modified leaves. As a result, when a corm is cut in half it is solid, but when a true bulb is cut in half it is made up of layers.^[1] Corms are structurally plant stems, with nodes and internodes with buds and produce adventitious roots. On the top of the corm, one or a few buds grow into shoots that produce normal leaves and flowers.

Gladiolus corm, showing the formation of small cormels at the end of short stolons

Cormels

Corms can form many small cormlets called cormels, from the basal areas of the new growing corms, especially when the main growing point is damaged. They are used to propagate corm forming plants. Corms of a number of species of plants are replaced every year by the plant with growth of a new corm; this process starts after the shoot has developed fully expanded leaves. The new corm forms at the shoot base just above the old corm. As the new corm is growing, short stolons are produced that end with the newly growing small cormels. As the plants grow and flower, the old corm is used up and shrivels away. The new corm that replaces the old corm grows in size, especially after flowering is done.

The old corm produces the greatest number of cormels when it is close to the soil surface. The small cormels normally take one or two more years of growth before they are large enough to flower.

Corms can be dug up and used to propagate or redistribute the plant (see, for example, taro). Plants with corms can be propagated by cutting the corms into sections and replanting. Each section with a bud will generate a new corm.

Roots

Many corms produce two different types of roots. Those growing from the bottom of the corm are normal fibrous roots, they are formed as the shoots grow, and are produced from the basal area at the bottom of the corm. The second type of roots are thicker layered roots that form as the new corms are growing, they are called contractile roots and they pull the corm deeper into the soil. They are produced in response to fluctuating soil temperatures and light levels. Once the corm is deep enough within the soil where the temperature is more uniform and there is no light, the contractile roots no longer grow and the corm is no longer pulled deeper into the soil.

Plants with corms

Cultivated plants that form corms include:

• Arisaema
• Bessera
• Banana ^[2]
• Brodiaea
• Crocosmia
• Crocus
• Dichelostemma
• Dierama
• Eleocharis dulcis (Chinese water chestnut)
• Ensete spp. (enset)
• Freesia
• Gladiolus
• Iris some species.
• Konjac
• Liatris
• Milla
• Musa
• Montbretia
• Romulea
• Saffron
• Sagittaria spp. (arrowhead or wapatoo)
• Tecophilaea
• Taro
• Xanthosoma spp. (malanga, cocoyam, tannia, and other names)

See also

• Rhizome
• Tuber
• Root vegetable

References