There are some stems that grow under the ground to store food. These underground stems swell and become thick.
There are four types of underground stems:
- Rhizome.
- Corm
- Tuber
- Bulb
1. Rhizome: It is an underground thick stem with nodes and intemodes with scale , leaves at the node. It grows horizontally and has an irregular shape. Rhizome have buds. It gives rise to new stem and leaves. E.g. Ginger and Turmeric.
2. Corm: This underground stem is round in shape and flat at the top and bottom. It
is a condensed form of rhizome and bears one or more buds in the axils of scale leaves. Daughter plants arise from their buds. E.g. Colocasia.
3. Tuber: It is an enlarged, spherical underground stem that stores food. It has many dormant buds on its surface known as “Eyes”. If we plant a part of tuber with the bud, it grows into a new plant. E.g. Potato.
4. Bulb: It is condensed stem which is disc like and stores food in the fleshy leaves. The bulb has two types of leaves.
- Fleshy Leaves
- Scaly Leaves
The upper part of the stem has a terminal bud and it is covered by many scaly leaves, the inner fleshy leaves store food as seen in Garlic and Onion.