Understanding the growth of bulb plants
Bulbs are one of the most beloved plants in the garden, and one of the most fascinating plants for the scientists. The way bulbs grow is a miracle of nature, and their unique design allows them to withstand temperature and weather extremes that would be lethal to other types of plants.
The plants known to the gardener as bulbs actually encompass five distinct types of structures – true bulbs, corms, rhizomes, tubers and tuberous roots. Each grows from an underground structure, but how those structures work is quite different.
A true bulb is an underground structure consisting of stem base that contains an embryonic plant. All the structures of the adult plant, including the flower buds, the leaves and the roots, are contained within this underground stem base. This design allows the plant contained within the bulb to lie dormant during periods of drought, heat waves or other extreme environmental conditions.
Some of the most beloved of all flowers, including daffodils, tulips and lilies, are true bulbs. While bulbs are generally very durable, it is important that they not be allowed to dry out.
Corms, unlike true bulbs, do not contain scales. The roots of the corm grow instead from a basal plate, while the growth plate is located on the top of the corm. Gladiolas and crocuses are perhaps the best known corms in the garden.
Tubers do not have basal plates, and the roots of the tuber grow both on the base and on the sides of the structure. Tubers have multiple growth points spread out along the top of the structure.
Rhizomes are actually thickened stems, and they grow either partially or completely underneath the ground. These rhizomes have a large growth point on one end, with the other growth points spread along the sides. The bearded iris the best known of the rhizomes in the garden.
Tuberous roots are not true roots, but specially adapted structures which are made to absorb water and nutrients from the soil. These plants tend to grow in a cluster, and the tuberous parts of the plant radiate out from the central structure. Daylilies and dahlias are both tuberous roots.
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