Modification of the Aerial Stem - Practice Questions & MCQ

Modification of the Aerial Stem 

• Whole stem or a part of it can be modified to perform additional functions.
• The identity of the stem remains because there is a clear demarcation of nodes and internodes and buds arising from the axils of the leaves.

Stem Tendrils:

• Stem or branches can be modified into green and coiled thread-like structures called tendrils.
• These develop from the axillary bud, the bud present in the axil of the leaf.
• These help the plants like cucumbers, pumpkins, watermelons and grapevines to climb.

Thorns:

• The axillary buds of stem can be modified to form straight, pointed, woody and hard structures called thorns.
• It arises in the axil of the leaf.
• They protect plants from grazing animals.
• These are found in Citrus, Bougainvillea etc.

Phylloclade:

• Phylloclades are modified aerial stem that are flattened or cylindrical.
• These are characterised by an unlimited growth with a number of nodes and internodes.
• Because this modification is a feature of xerophytic plants, the leaves are reduced to spines to check transpiration whereas the stem performs photosynthesis.
• It also stores water.
• For example, Opuntia (flattened phylloclade), Euphorbia (cylindrical phylloclade).

Cladode:

• These are the modification of lateral branches with limited growth and limited nodes and internodes.
• These appear like flattened leaves and perform photosynthesis.
• In asparagus, the cladodes are one internode long while in Ruscus, these are two internodes long.

Bulbils 

• These are the modified vegetative or floral buds.
• These store food and serve as propagules for vegetative propagation.
• For example, in Dioscorea, the axillary buds condense to form the bulbils while in Agave, the floral buds are modified to develop bulbils.
• They detach from the parent plant and develop into a new plant.