Question

Describe the structure and function of five types of modified stems. (15 Marks)

Answer 1

Five types of modified stems will be discussed below:

1. Rhizomes:

Structure: It is fleshy and non green underground stem. It has very distinct nodes and internodes. The nodes have dry scale leaves which have axillary buds. Terminal buds are present. From the lower side, adventitious roots arise. When, the rhizome grows obliquely it is called root stock rhizome (ex, Banana) and when they grow horizontally they are called straggling rhizome (ex. Ginger).

Function: It acts as a food source.

2. Bulb:

Structure: A terminal bud and many fleshy scale leaves are present. Cluster of adventitious roots arise from base of the bulb. The bulbs may be scaly or tunicated. A sheath of dry membranous scale leaves, called tunic covers the tunicated bulb. Ex: garlic. In case of garlic, the bulb contains an aggregate of cloves or bulblets, each is covered by its individual tunic. The scaly bulb does not have any tunic. Ex: Lily.

Function: A bulb’s fleshy leaves function as food reserves which enables a plant to lie dormant when water is unavailable.

3. Corm:

Structure: It is a condensed form of rhizome which grows in vertical direction. It is spherical with a flattered base. The corm possesses distinct circular nodes and internodes. The nodes bear scale leaves and axillary buds. Adventitious roots originate either from its base or all over the body. Ex: colocasia.

Function: Corms serve as food organs and it functions as an organ of vegetative reproduction.

4. Tuber:

Structure: Stem tuber is a swollen tip of a stolon, which is an underground lateral Stem. It is covered by a skin with a number of small depressions called eyes. Each eye is a node and bears one or multiple buds subtended by a leaf scar. A big scar at heel end of a potato marks its attachment to the stolon. Adventitious roots are absent. Ex: Potato.

Function: Stores food

5.Runner:

Structure: It is a creeping stem with long internodes and runs horizontally on the soil surface. The nodes have axillary buds, scale leaves and adventitious roots. From an axillary bud, runner arises. Runners break off to grow into individual plants, and helps in vegetative propagation. Ex: Lawn grass. An underground runner is called as sobole. Ex: Agropyron.

Function: Helps in vegetative propagation

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