Stems
Some stems have been modified to perform special functions such as food storage, reproduction, protection or support. Stems for food storage, have been modified the following ways:
Rhizomes - thick horizontal stems that grow under soil. E.g. ginger, lengkuas, lotus 'root', turmeric
Tubers - swollen underground stems for food storage. E.g. potato
Corms - swollen short stem with some thin leaves for food storage. E.g. water chestnut.
However, all modified stems are true stems and have nodes (points where leaves, branches and other appendages arise) on their surface. A good example is the potato. This tuber has small scale-like leaves and tiny buds known as eyes. The eyes can sprout into new plants.
Roots
There are two main types of root systems:
Taproot system - The first root to grow is the primary root, which eventually produces many branches called secondary roots. These may branch further. The primary root continues to grow remain larger than any of the secondary roots.
Fibrous root system - The primary root also produces many secondary roots. However, the secondary roots grow in all directions and there is no prominent primary root.In some plants, the taproots become swollen or fleshy due to storage of food. Some examples are beets, carrots, Chinese radish, horseradish, radish, sweet potatoes, tapioca, turnip and yam beans. These roots are distinguished from underground stems by lacking nodes or leaf scars (left after a leaf has dropped off) and by having its growing tip protected by a root cap.
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