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. Corms are not
bulbs 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. 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. [edit]Plants with
corms Cultivated plants that form corms include: Arisaema Bessera
Banana [1] Brodiaea Crocosmia Crocus Cyclamen 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)