. Explain Aerial Modification of Stem With Diagram
AERIAL MODIFICATIONS OF STEM
To perform some special functions like climbing, protection, food manufacture, vegetative reproduction, etc., vegetative and floral buds often undergo modification in certain plants. The various aerial modifications of stem are as follows:
1. Phylloclade or cladophyll: It is a green, flattened or cylindrical, thick, succulent modified main stem. It has several distinct nodes (areoles, the raised areas) and internodes. Leaves get modified into scales or spines. It is an adaptation of plants of xerophytic conditions. It serves as photosynthetic and storage organ e.g., prickly pear (Opuntia tuna), cocoloba (Muchlenbeckia platyclados), several species of Euphorbia, Prunus, etc.
2. Cladode: It is similar to phylloc1ade with the difference that it may be made up of only one internode, e.g., satavar (Asparagus racemosus) or two internodes e.g., butcher's broom (Ruscus aculeatus). It is a modified branch arising from axillary bud. Leaves are reduced to scales or spines. It performs the function of foliage leaves.
3. Thorns: It is a hard, straight and pointed structure meant for protection. It may arise from axillary bud, e.g., garden hedge plant (Duranta), lemon (Citrus), pomegranate (Punica), etc. or from apical bud, e.g., karonda (Carissa). It may bear leaves, flowers and fruits, e.g., Duranta, Prunus, etc.
4. Stem tendril: It is a thin, wiry, leafless, spirally coiled and sensitive structure meant for climbing. It may be branched or unbranched. Branched stem tendrils may bear scale leaves in the region of forking. It may arise from axillary bud, e.g., passion flower (Passiflora suberosa) or from apical bud, e.g., Vitis, or from extra-axillary buds, e.g., Cucurbits, or from floral bud, e.g, sandwitch island climber (Antigonon) and balloon vine (Cardiospermum).
5. Bulbil: It is a special multicellular body meant for vegetative reproduction. It may be the modification of a vegetative or floral bud. It gets swollen because of accumulation of food. It gets detached from the mother plant and grows into a new independent plant e.g., Dioscorea, Oxalis, Globba, Agave, Allium, Lilium, etc.