What Sets Corms Apart from Bulbs in Plant Biology?
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A Gladiolus corm and an onion bulb
What are Corms and Bulbs?
The stem is modified into various forms in different plants to suit their adaptation needs. These modifications can be underground, aerial, or even sub-aerial. Underground modifications of stems consist of rhizomes, bulbs, corms, and tubers. They may resemble the plants' roots, but they differ in the presence of nodes and internodes, leaves, and buds. The main reason for the development of stem modifications is to allow the plant to survive in all kinds of environments and habitats, which are distinct from the regular ones.
Nature has modified stems and made them capable of performing the functions of food storage, plant support, protection, and vegetative propagation. These types of plants come under the category of Geophytes. Both corms and bulbs need a rest period that follows a time of active growth. Garlic is an example of a bulb, while corm examples are crocus, gladiolus, autumn crocus, etc.
Let us study two such underground stem modifications, the corm, and the bulb, and the difference between corm and bulb.
What is a Corm?
A corm is a swollen, underground plant stem modification that is present in some plants. Corms are built for nutrients and food that the plant can use in due course of time. These nutrients are generally stored in the corm during one growing season. They help produce various parts of the plants, like, roots, leaves, and flowers, for the next growing season of the plant.
Corms look similar to bulbs but are different from them as they do not possess the layered scales present in the bulbs. Corms reproduce via cormlets or individual corms. These cormlets can be separated from the parent to produce exact copies of the plant.
Corms are flattened or slightly round in appearance. Roots can grow from the corm base under the soil. In most cases, the parent corm dies back, and the corm lets it become the source of the plant the next year. The corm has membranous to scaly leaves and absorbs nutrients. It stores them for the next season. The corm can be divided and transplanted into other areas of the garden for vegetative propagation. Gladiolus, crocus, and crocosmia are classic corm examples.
What is Bulb?
A bulb is another stem modification. Most perennial monocotyledons have this form of a stem that provides a resting stage to their seeds. A bulb has a large, central bud that grows underground and is usually globe-shaped. The center of the bulb contains a bud that produces leaves and flowers. It also has membranous or fleshy leaves that arise from a short stem. A cluster of adventitious roots arises from the bulb base. The lateral buds give rise to shoots of the bulb. The plant’s food is stored in the leaves. New bulbs replace the old bulbs as they grow.
Onion is the best example of a bulb, apart from garlic. Lily plants, tulips, and hyacinths are also bulb plants. Some bulbs are grown for their decorative flowers, like, lily, tulip, and iris.
Difference Between Corm and Bulb
Now that we know what is a corm and a bulb and how they store food let us try to distinguish between the two. The table given below provides the difference between corm and bulb.
Fun Facts
The largest corm is that of Titan Arum that weighs more than 150 kg.
FAQs on Corm vs Bulb: Understanding the Differences
1. What is the main structural difference between a corm and a bulb?
The main difference lies in their composition. A corm is a solid, swollen underground stem. In contrast, a bulb consists of layers of fleshy, modified leaves (called scales) that are attached to a short stem base. If you were to cut them open, a corm is solid all the way through, while a bulb has visible rings like an onion.
2. What is a corm and what is its primary function?
A corm is a short, vertical, swollen underground plant stem that acts as a storage organ. Its main purpose is to store food, mostly starch, which helps the plant survive unfavourable conditions like winter or drought and provides energy for growth in the next season.
3. What is a true bulb made of?
A true bulb is essentially an underground bud. It has a short, compressed stem at its base and is surrounded by layers of fleshy, modified leaves called scales. These scales are the primary parts that store food. The centre of the bulb holds the bud for the next year's flower and leaves.
4. Can you give some common examples of corms and bulbs?
Certainly! Here are some common examples to help you distinguish them:
- Corms: Plants like Gladiolus, Crocus, and Taro (Arbi) grow from corms.
- Bulbs: Well-known plants that grow from bulbs include Onion, Garlic, Tulip, and Lily.
5. Is an onion a bulb or a corm?
An onion is a perfect example of a bulb. When you slice an onion, you can see the distinct concentric rings. These rings are the fleshy, modified leaves that store food for the plant. A corm, in comparison, would be solid inside without any layers.
6. Why are both corms and bulbs considered modified stems and not roots?
This is an excellent question. They are classified as modified stems because they possess key stem-like features that roots do not have. For example, they have nodes (points where leaves and buds attach) and internodes (the spaces between nodes). They can also produce buds that grow into new shoots and leaves, which is a fundamental characteristic of stem tissue.
7. How do the food storage methods differ between a corm and a bulb?
While both store food, the location of storage is different. In a corm, the food is stored directly within the solid, swollen stem tissue itself. In a bulb, the food is stored in the fleshy, modified leaves (scales) that are attached to the stem base. So, the stem is the primary storage organ in a corm, whereas the leaves are the primary storage organs in a bulb.
8. How do corms and bulbs compare to other storage structures like tubers and rhizomes?
All are underground stems modified for storage, but they are structurally different:
- Corm: A solid, vertical, swollen stem base (e.g., Gladiolus).
- Bulb: A short stem base with fleshy leaf layers (e.g., Onion).
- Tuber: The swollen, fleshy end of an underground stem branch, which has 'eyes' or nodes (e.g., Potato).
- Rhizome: A horizontal underground stem that grows sideways and has nodes that can sprout new roots and shoots (e.g., Ginger).
